JP4126117B2 - Flowmeter - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
This invention , A flow meter that measures the flow rate of a fluid using a pulse signal having a frequency corresponding to the flow rate from the sensor ,as well as The flow rate of comparing the measured flow rate with a preset flow rate value and outputting a digital output corresponding to the comparison result to an external device Total About.
[0002]
[Prior art]
As a device for measuring a signal from a sensor that detects a physical quantity to be measured and generates a pulse signal, a frequency meter, a tachometer, a pulse counter, and the like are known.
For example, a capacitive pressure sensor constitutes an oscillator and generates a signal having a frequency corresponding to pressure. Therefore, the pressure can be measured by measuring the frequency of the signal from the pressure sensor. In the impeller-type flow rate sensor, the magnetized impeller rotates by the flow, and the fixed Hall element detects the magnetism and outputs a pulse signal having a frequency corresponding to the flow rate. The flow rate can be measured by measuring the frequency of the pulse signal.
[0003]
One such physical quantity measuring device is a Karman vortex flow sensor. This Karman vortex flow sensor detects the frequency of Karman vortex streets alternately generated from both sides of a columnar vortex generator provided in a flow path by means of an ultrasonic sensor or a piezoelectric element sensor to detect gas, liquid, etc. It measures the flow rate of fluid.
The flow rate measurement range and the Karman vortex generation frequency corresponding to the flow rate are determined by the diameter of the flow path and the material of the pipe portion of the flow rate sensor. Here, assuming that the frequency value is f, the instantaneous flow rate value Q is obtained by the following linear expression (1).
Q = a × f + b (1)
In addition, since it is difficult to ensure accuracy in the above formula (1), the flow rate measurement range is divided into a plurality of n sections, and each section i (i = 1 to n) as shown in the following formula (2). ) To secure a full scale accuracy of about ± 1% (Japanese Patent Laid-Open No. 60-238720).
Q = ai × f + bi (2)
To further improve the accuracy, the ai and bi values are determined for each unit, the individually determined values Ai and Bi are stored in RAM or EEPROM, and the full scale is calculated by the following equation (3). It has also been proposed to ensure an accuracy of ± 0.5% (Japanese Patent Application No. 9-345742).
Q = Ai × f + Bi (3)
Here, Ai and Bi (i = 1 to n) are corrected coefficients determined for each device.
[0004]
Also, the measurement accuracy of the frequency value f becomes a problem. Generally, when measuring the frequency of a pulse signal, the number of pulses input within a predetermined period (gate time) is counted, or the period of the input pulse is measured, and the frequency is calculated from the reciprocal thereof. Things have been done. However, in the flow rate measurement, as is clear from the above equation, the frequency of the pulse generated at a high flow rate is high (the cycle is short), and low at a low flow rate (the cycle is long). Therefore, it is required to obtain a predetermined measurement accuracy at both a large flow rate and a small flow rate.
[0005]
Therefore, a frequency measuring device is proposed that includes a timer for a fixed time, a clock generator, a counter for clock counting, a counter control means for controlling the counting operation by the clock, and a processing means for detecting and counting pulse signals and performing predetermined arithmetic control. (JP-A-5-297036).
According to this frequency measuring apparatus, a time that is at least twice the period of the measurement lower limit frequency is set in the timer, and detection and counting of pulse signals are started. When the pulse signal is detected, the counter control means is controlled so that the clock counting counter starts counting the clock from the clock generator, and every time the pulse signal is detected, the clock counting counter Check the count value. When the count value does not reach the predetermined value, detection and counting are continued. On the other hand, when the count value reaches a predetermined value, the detection and counting are stopped, and the counter control means is controlled to calculate the frequency measurement value from the count value of the clock counting counter by calculation. At the end of the timer timing, if the clock counting is not completed, the detection and counting of the pulse signal is stopped, and the counter control means is controlled to complete the counting by the clock counting counter.
As a result, the N cycles of the pulse signal are counted by the clock counting counter, and the integration of the cycles is continued until the count value secures a desired resolution, so that a certain value or more can be obtained regardless of the frequency value of the pulse signal. The measurement resolution is obtained.
[0006]
In addition, a Karman vortex air flow sensor output pulse average period calculation device has been proposed that aims to improve the calculation accuracy of the average period at a large flow rate and improve the responsiveness at a small flow rate. No. 5-70086).
The average period calculating device includes a pulse number counting means, a pulse period measuring means, a pulse period comparing means for comparing the measurement period with a first predetermined time, and a first pulse number counting means from the end of the previous average calculation. When the number of pulses corresponding to the predetermined value is counted, when a large comparison result is output from the pulse period comparing means for the number of times corresponding to the second predetermined value, and when the number is reduced from the pulse period comparing means An average period for calculating the average of the period of the pulse signal every time one of the conditions is satisfied when a state in which a large comparison result is output subsequent to the comparison result appears the number of times corresponding to the third predetermined value And a calculating means. Furthermore, a second average period calculating means for calculating an average period based on a comparison result between the second predetermined value and the pulse period comparing means, or a second means for comparing the measurement period with a second predetermined time. The apparatus further includes second average period calculating means for calculating an average period based on outputs of the pulse period comparing means and the second pulse period comparing means.
With these configurations, the average period of the pulse signal input from the sensor can be quickly calculated over a small flow rate, a medium flow rate, and a large flow rate.
[0007]
On the other hand, in such a flow sensor (flow meter), a flow rate measured as a flow rate transmitter or a flow rate transmitter is converted into a predetermined signal form and a signal is output to an external device. Generally, in such a flow rate transmitter, 8-bit digital data corresponding to a measured value is converted into the predetermined signal form and transmitted.
Further, in such a flow meter, there is also known a device in which the measured flow rate (instantaneous flow rate) is integrated to calculate an integrated flow rate, and the display unit displays not only the instantaneous flow rate but also the integrated flow rate.
[0008]
Furthermore, as an application example of such a flow meter, the flow rate of the fluid flowing through the flow path is compared with a preset reference flow rate value (set flow rate value), and a signal for controlling an external device is output based on the comparison result. A flow rate detection switch has been proposed (Japanese Patent Laid-Open No. 9-89613).
In this proposed flow rate detection switch, the cycle of a pulse signal having a frequency corresponding to the generation cycle of Karman vortex is measured, and the flow rate value is obtained by referring to a table based on the measured cycle. In order to improve measurement accuracy, the period of a plurality of pulses is measured and averaged. Then, the preset threshold value is compared with the measured flow rate, and the comparison result is displayed by the LED, and the collector is applied to the base of the transistor connected to the output terminal and connected to the output terminal. The power supply to the load is controlled.
[0009]
[Problems to be solved by the invention]
In general, the frequency measurement method for counting the number of input pulses has a problem in that the resolution of measurement at a low frequency input is coarse and accuracy cannot be obtained regardless of the gate time value. For example, if the gate time is 1 second as described above, an accuracy of ± 0.5% cannot be obtained unless the frequency is 200 Hz or higher.
Further, in the case of period measurement, there is a problem that the resolution of measurement at a high frequency input is rough and accuracy cannot be obtained regardless of the length of the period or the value of the measurement reference clock. For example, a count number of 200 or more is required.
[0010]
In addition, since the frequency measuring apparatus described above uses a timer in which a time that is twice or more the period of the measurement lower limit frequency is set, when measuring a frequency near the measurement lower limit frequency, 2 of the period. More than twice the measurement time is required. In addition, before the timer time expires, the period of N times of the pulse signal is counted by a clock counting counter, and when the count value reaches a predetermined value, detection and counting are stopped, and the count value The frequency measurement value is calculated from In this case, since the entire set time of the timer is not measured, there is a problem that the true frequency measurement of the input pulse signal is not performed.
[0011]
In addition, according to the above-described average period calculation device, it is possible to quickly calculate the average period of the pulse signal input from the sensor over a small flow rate, a medium flow rate, and a large flow rate by setting four to five parameters. However, since the pulse number counting means, the pulse period measuring means, the first and second pulse period comparing means, and the first and second average period calculating means are used, the configuration becomes complicated. Also, when the processing by each of these means is executed by a microcomputer or the like, the program requires a large amount of memory, and the time required for the processing becomes long, and the ratio occupied in the average period calculation processing is large. There was a problem that there was no room to execute the process.
[0012]
Further, as described above, in the flow rate transmitter, 8-bit digital data corresponding to the measured value is converted into the predetermined signal form and transmitted. In this case, because the digital quantization error is ± 1 digit, the error is about ± 0.4%. When high-precision detection is performed and a high-quality signal is to be sent to an external device, the error is propagated. This indicates that it is necessary to use digital data having more bits than 8 bits in order to prevent it.
[0013]
Furthermore, in the conventional flowmeter having a function of displaying the integrated flow rate value, the integrated flow rate is only displayed by a fixed-point method, and it is very inconvenient to know the integrated flow rate value over a long period of time. There was a problem that there was.
Furthermore, as described above, in the Karman vortex flow sensor, the flow rate measurement range and the Karman vortex generation frequency are determined by the diameter of the flow path and the material of the piping part of the flow sensor. There is a need to easily adapt the type of flow meter to the piping section into which it is inserted.
[0014]
Furthermore, in the above-described flow rate detection switch, the Karman vortex generation cycle is measured. Therefore, when the frequency is high, the cycle is shortened, the measurement resolution cannot be obtained, and the measurement accuracy is deteriorated. There was a problem. In addition, since the flow rate is determined by referring to the data table from the frequency obtained from the reciprocal of the cycle, one flow rate data is defined for one frequency, and a huge amount of memory is required. There was a problem that many kinds of microcomputers had to be prepared because data tables and control programs of various kinds of calibers could not be accommodated in one microcomputer.
Furthermore, the flow rate detection switch may require a high-speed switch output depending on its application. For example, in a welding gun, electric discharge machine, etc., when the flow rate detection switch is disposed in the flow path of the cooling water and an abnormality such as chip removal is detected due to an abnormality in the flow rate of the cooling water, In order to prevent burning, high-speed switch output is required.
[0015]
Therefore, the present invention can perform high-speed and high-precision measurement with a simple configuration. Flowmeter The purpose is to provide.
Also easy to handle, easy to operate, low price Rated The purpose is to provide a flow meter.
Furthermore, it aims at providing the flowmeter excellent in practicality by increasing the substantial display digit number of an integrated flow value.
It is another object of the present invention to provide a flow meter capable of easily selecting the characteristics of a flow path by operating a key operation unit.
Furthermore, when the instantaneous flow rate is detected and used as a switch (sending an output signal to an external control device installed at a remote location) in comparison with the set value, it is easy to check and change the set value. The flow rate is easy to use for the operator without any setting or operation errors. Total The purpose is to provide.
It is another object of the present invention to provide a flow meter capable of operating a switch output at a high speed when an abnormality occurs in the fluid flow.
Furthermore, the flow rate at which the transmission signal can be output at a predetermined timing. Total It is intended to provide.
Furthermore, the flow rate that can send a good quality transmission signal to external devices Total It is intended to provide.
[0018]
[Means for Solving the Problems]
In order to achieve the above object, a flow meter of the present invention includes a sensor unit that outputs a pulse signal having a frequency corresponding to a flow rate to be measured, and a first signal that generates a first signal having a first period. A generator, a first measuring unit that counts the number of pulses output from the sensor unit during the period of the first cycle in response to the first signal, and the first signal during the cycle Based on the second measurement unit for measuring the position of the first signal in the pulse included in the first measurement unit, the count value by the first measurement unit, and the measurement result by the second measurement unit. A flowmeter having a first calculation unit that calculates the frequency of the pulse signal every time and a second calculation unit that calculates an instantaneous flow rate based on the calculated frequency of the pulse signal, And the first period Measure A second signal generator for generating a second signal having a second period divided by the lower limit frequency And means for invalidating the measurement result when a state in which the period of the pulse in the pulse signal is equal to the period corresponding to the commercial AC power supply frequency continues for a predetermined number of times. Have Above The timing of the calculation operation of each calculation unit is controlled based on the output of the second signal generation unit.
[0019]
Also Of the present invention other The flow meter includes a sensor unit that outputs a pulse signal having a frequency corresponding to a flow rate to be measured, a first signal generation unit that generates a first signal having a first period, and a response to the first signal. A first measurement unit that counts the number of pulses output from the sensor unit during the period of the first cycle, and a position of the first signal in a pulse that includes the first signal in the cycle A frequency of the pulse signal is calculated for each of the first periods based on a second measurement unit that measures the frequency, a count value obtained by the first measurement unit, and a measurement result obtained by the second measurement unit. 1 is a flow meter having a first calculation unit and a second calculation unit that calculates an instantaneous flow rate based on the calculated frequency of the pulse signal, the preset set flow rate value and the second calculation unit. A comparison unit for comparing the instantaneous flow rate value calculated by A switch output unit that outputs a result as a digital signal, and the comparison unit includes an instantaneous flow rate value calculated based on an output of the first calculation unit and the set flow rate value for each first period; The first mode and the normal mode for comparing Measure It has two operation modes of a high speed mode for comparing the instantaneous flow rate value calculated based on the measurement value of the first measurement unit and the set flow rate value every second period divided by the lower limit frequency. is there.
Further, a plurality of values can be set as the set flow rate value, and the switch output unit is controlled by a logical sum of comparison results for the plurality of set flow rate values.
[0026]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 illustrates the present invention. Flow meter Frequency measurement with frequency measurement method applied Part It is a block diagram which shows the example of a structure. In this figure, reference numeral 1 denotes a frequency detector that outputs a pulse signal to be measured. 2 is a first counter, 4 is a first timer that generates a first signal that defines the start and end points of measurement, and the first counter 2 is defined by a first signal from the first timer 4. The number of input pulses input during the period from the measurement start time to the measurement end time is counted. 3 is a second counter, 5 is a reference clock generator for generating a reference clock signal, and the second counter 3 is input from the rising edge (or falling edge) of the input pulse from the frequency detector 1 to the next input. The period of the input pulse is measured by counting the reference clock input from the reference clock generator 5 during the period up to the rising edge (or falling edge) of the pulse. As shown in the figure, the first signal from the first timer 4 is applied to the second counter 3 as a control signal, and the second counter 3 measures the timing at which the first signal is generated. Numeric values can be output.
An arithmetic processing unit 6 calculates the frequency of the input pulse signal based on count outputs from the first counter 2 and the second counter 3. 8 is a display unit that displays the frequency calculated by the arithmetic processing unit 6, 9 is an output unit that outputs the calculated frequency to an external device, and 7 is a control unit that controls the operation of each component. .
Note that the first counter 2, the second counter 3, the first timer 4, the reference clock generation unit 5, the arithmetic processing unit 6 and the control unit 7 surrounded by a broken line in the figure can be configured by, for example, a single chip microcomputer. it can.
[0027]
Configured like this Frequency measurement section Of the present invention implemented in Flow meter The measurement principle in the frequency measurement method will be described with reference to FIG. In this figure, (a) is an example of an input pulse signal from the frequency detector 1, (b) is a first signal output from the first timer 4, and (c) is a total of the first counter 2. A numerical value (d) indicates the count content in the second counter 3. Here, the first signal of (b) defines the measurement start point and measurement end point in this frequency measurement, and can be a signal having a period according to the frequency of the pulse signal to be measured. In order to simplify the explanation, here, the output signal has a period of 1 second. Note that, by setting the measurement end point as a measurement start point in the next measurement cycle, the frequency can be continuously measured for each cycle of the first signal (first cycle). Further, the period of the reference clock for measuring the period of the input pulse signal determines the accuracy of the measurement. Here, it is assumed that the clock signal has a period of 1 msec.
[0028]
Now, the first counter 2 counts the number of pulses input in the measurement period (in this example, 1 second) from the measurement start point to the measurement end point defined by the first signal. At this time, counting can be performed using either rising or falling of the input pulse, but here, the rising of the input pulse is counted. In the example shown, 5 pulses are counted. In this case, since the measurement period is 1 second, this value of 5 corresponds to the integer part of the frequency of this input signal.
[0029]
However, by simply counting the number of pulses in this way, as shown in FIG. 2A, the count value is obtained for the period A from the counting start time to the rising edge of the first pulse (pulse 1). It is not reflected in. Further, the fifth pulse (pulse 5) is counted as being included in the period B from the measurement end point to the rise of the next pulse (pulse 6). Therefore, in order to accurately measure the frequency of the input pulse signal, it is necessary to consider the A and B portions.
That is, the ratio of the period A from the measurement start time to the rise time of the pulse 1 in the period T1 of the pulse 0, and the period T2 of the pulse 5 in the period B from the measurement end point to the rise time of the pulse 6 By calculating the ratio of the number of pulses, and correcting the number of pulses, an accurate frequency f can be obtained.
[0030]
In order to measure part A and part B described above, the frequency measurement Part As shown in FIG. 2D, the second counter 3 starts counting the reference clock at the rising edge of the input pulse signal and the count value (N1) at the rising edge of the next input pulse signal. ) And the counting starts again from 0. When the first signal from the first timer is input during the counting, the count value (n1) at that time is output. Thereby, the count outputs N1, N2, n1, and n2 respectively corresponding to the times T1, T2, t1, and t2 described above can be obtained. If there is no input of the first signal during the measurement of the period of the input pulse, the measured value may be discarded and the next measurement may be performed.
Then, the arithmetic processing unit 6 calculates the following equation (4) based on the count value f0 from the first counter 2 and the count values N1, N2, n1, and n2 from the second counter 3. The frequency value f is calculated.
f = f0 + (1-n1 / N1)-(1-n2 / N2)
= F0-n1 / N1 + n2 / N2 (4)
[0031]
In the above description, the measurement period (the period of the first signal) has been described as being 1 second. However, this period can be set to an arbitrary value according to the signal frequency to be measured. Is T seconds, the frequency value f can be obtained by the following equation (5).
f = (f0−n1 / N1 + n2 / N2) × (1 / T) (5)
[0032]
Of the present invention described above Flow meter In the frequency measurement method, when there are one or more pulses input during the measurement period, the frequency can be calculated using the above equation (5). Therefore, high-accuracy frequency measurement is possible in a measurement period equal to or greater than the period of the measurement lower limit frequency, and it is not necessary to lengthen the measurement time in order to improve accuracy as in the conventional measurement method. For example, when the measurement lower limit frequency is 1 Hz, the frequency can be accurately measured in a measurement period of 1 second when the measurement lower limit frequency is 5 Hz.
The measurement accuracy at the measurement lower limit frequency is determined by the period of the reference clock. For example, if the period of the first signal is 1 second (measurement lower limit frequency is 1 Hz) and the required resolution is 200 (accuracy ± 0.5%), the reference clock may be 5 msec, When the resolution is 1000 (accuracy ± 0.1%), the reference clock may be 1 msec. If the measurement lower limit frequency is 5 Hz, the period is 200 msec. Therefore, if the reference clock is 1 msec, a resolution of 200 can be obtained.
[0033]
Thus, the present invention Flow meter According to the frequency measurement method, the period of the input pulse included in the measurement period from the measurement start point to the measurement end point can be accurately calculated to the fractional part, and the frequency of the input pulse signal can be calculated as the length of the measurement period. It is possible to calculate with high accuracy regardless of the above.
When the measurement is repeated continuously, the decimal part at the measurement end point (the decimal part corresponding to the time B) corresponds to the decimal part at the measurement start point in the next measurement (corresponding to the time A). And the arithmetic processing is simplified, and accurate frequency data can be obtained for each cycle of the first signal.
In the above description, the measurement of the cycle is started at the rising time of the input pulse. However, it is obvious that the measurement may be started at the falling time.
Further, when 200 ≦ f0 as a result of the measurement by the first counter 2, a measurement accuracy of 0.5% can be obtained without calculating the measurement result of the second counter 3. Processing can be omitted.
[0034]
The frequency measurement shown in FIG. 1 that operates based on the measurement principle described above. Part Will be described in detail with reference to the flowcharts of FIGS. For the sake of simplicity, here, it is assumed that the first period is set to 1 second.
Here, the portion surrounded by a broken line in FIG. 1 is constituted by a single chip microcomputer (hereinafter simply referred to as a microcomputer), and the first counter 2 and the second counter 3 are built-in counters of the microcomputer. The first timer 4 and the reference clock generator 5 are built-in timers of the microcomputer. And the said control part 7 calculates the frequency of an input pulse using the arithmetic processing part 6 according to the program stored in the program memory which is not shown in figure.
[0035]
Below, this frequency measurement Part Will be described with reference to the flowcharts shown in FIGS. 3 to 5 and the time chart of FIG. Figure 3 shows this frequency measurement. Part FIG. 4 is a flowchart of a first timer interrupt processing routine started by a first signal from the first timer 4, and FIG. 5 is a rising edge (falling edge) of the input pulse. 5 is a flowchart of a counting process routine of a second counter activated by an interrupt generated by
The control unit 7 proceeds with processing based on various flags such as a sequential storage flag 1 and a sequential storage flag 2, an operation permission flag 1, an operation permission flag 2, and a second counter valid flag. Here, the sequential storage flags 1 and 2 are flags that are set at the start of the operation, and the calculation permission flags 1 and 2 are flags that indicate the timing at which the calculation processing unit 6 should execute the calculation for calculating the frequency. The counter valid flag is a flag indicating that it is time to store the count contents of the second counter 3 in a register.
[0036]
This frequency measurement Part 3 is started (timing t0 in FIG. 6), the main routine shown in FIG. 3 is started. First, in step S1, initialization processing of each unit such as initialization of each register is performed. In step S2, the sequential storage flag 1 and the sequential storage flag 2 are both set, and the calculation permission flags 1 and 2 and the second counter valid flag are reset. Next, the time measurement of the first timer 4 is started in step S3. Thereby, the interruption process (FIG. 4) from the first timer 4 is executed after the first period. Next, in step S4, the counting of the first counter 2 is started. Subsequently, in step S5, the interruption by the rising edge of the input pulse is permitted. Thereby, the counting process (FIG. 5) of the second counter 3 is executed at the timing of the rising edge of the input pulse. Instead of interrupting with a rising edge, it may be performed with a falling edge.
[0037]
Next, the process proceeds to step S6, where it is determined whether or not the calculation permission flags 1 and 2 are both set. As described above, immediately after the operation is started, since both the calculation permission flags 1 and 2 are reset, the result of this determination is NO. On the other hand, when the result of this determination is YES, the process proceeds to step S7, where the frequency f is calculated based on the equation (4), and the calculation permission flags 1 and 2 are reset (step S8). When the determination result of step S6 is NO or after the process of step S8 is completed, the display and output process of step S9 and other processes of step S10 are executed, and the processes after step S6 are repeated again. Executed.
[0038]
FIG. 4 is a process flowchart of a first timer interrupt process activated by a signal of the first period by the first timer 4. As described above, when the operation is started at time t0, this processing is started at time t1. First, in step S11, the timing of the first timer is restarted. This guarantees the first timer interrupt at the correct timing (t2, t3,...). Next, in step S12, the count value of the first counter at this time is stored in the register f0, and in step S13, the first counter is initialized, and the count of the first counter is started again. As a result, the number of input pulses for each first period can be stored in the register f0. In this case, the number of pulses input in one second from t0 to t1 is stored in the register f0.
[0039]
In step S14, it is determined whether the sequential storage flag 1 is set. As described above, the sequential storage flag 1 is set in step S2 (FIG. 3), and the determination result is YES when interrupted by the first signal at time t1. At this time, the process proceeds to step S15, and the count value (nt1) of the second counter at this time is stored in the register n2 and also stored in the register n1 (step S16). In step S17, the sequential storage flag 1 is reset. As a result, the count value nt1 corresponding to the time from the rising edge of the input pulse immediately before time t1 to time t1 is stored in the registers n1 and n2.
[0040]
On the other hand, in the first timer interrupt processing routine after time t2, since the storage flag 1 is sequentially reset in step S17, the determination result in step S14 is NO. In this case, in step S18, the count value of the second counter at the previous interrupt stored in the register n2 is transferred to the register n1, and the count value of the second counter at this time is transferred to the register n2. To store. That is, at the time of interruption at time t2, the count value nt1 at time t1 is transferred to the register n1, and the count value nt2 of the second counter at time t2 is transferred to the register n2.
After step S17 or S19 is executed, the second counter valid flag is set in step S20. Further, in step S21, the calculation permission flag 1 is set, and this first timer interrupt processing routine is executed. finish.
[0041]
FIG. 5 is a flowchart of the counting process routine of the second counter. As described above, this routine is triggered by the rising (or falling) edge of the input pulse. When an interrupt is generated at the rising edge of the input pulse, it is first determined whether or not the second counter valid flag is set (step S22). As described above, the second counter valid flag is reset when the main routine is started (step S2), and is set in step S20 of the first timer interrupt processing routine. Therefore, before the time t1 shown in FIG. 6, the second counter valid flag is in a reset state. Therefore, in this interrupt processing routine started by the rise of the input pulse by this time, the determination result in step S22 is NO, so the process proceeds to step S23, and the second counter is reset to zero. Then, the measurement of the cycle of the input pulse is resumed. As will be apparent from the description below, the frequency calculation process (step S7) is executed in the main routine, the calculation permission flags 1 and 2 are reset (step S8), and then the first signal is generated. Even during the time until the timing (t2, t3,...), The determination result of this step S22 is NO, and at these times, the second counter simply repeats the measurement of the period of the input pulse.
[0042]
On the other hand, the interrupt processing routine immediately after execution of step S20 (FIG. 4) in the first timer interrupt processing routine (second time due to the rising edge of the input pulse immediately after times t1, t2, t3... In FIG. 6). In the counter counting process routine), since the second counter valid flag is set, the determination result in step S22 is YES. At this time, the process proceeds to step S24, where it is determined whether the sequential storage flag 2 is set. As described above, the sequential storage flag 2 is set in step S2 of the main routine immediately after the start of operation. In this interrupt processing routine by the rising edge of the input pulse immediately after time t1 shown in FIG. The determination result in step S24 is YES. Therefore, at this time, the process proceeds to step S25, and the count value of the second counter (Nt1 in FIG. 6) at this time (the time when the input pulse rises immediately after time t1) is stored in the register N2 and also stored in the register N1. (Step S26). In step S27, the sequential storage flag 2 is reset. Thereby, the cycle Nt1 of the input pulse including the first signal at the time t1 in the cycle is stored in the registers N2 and N1.
[0043]
On the other hand, after the time t2, since the sequential storage flag 2 is reset in the step S27, the determination result in the step S24 is NO. At this time, in step S28, the count value of the second counter stored in the register N2 (Nt1 in the interrupt process immediately after time t2) is transferred to the register N1 and the register The count value of the second counter at this point (Nt2 in this interrupt process immediately after time t2) is stored in N2 in the register N2 (step S29). As a result, the cycle of the input pulse including the generation timing of the first signal in the cycle can be stored in the register N2, and the generation timing of the input pulse including the generation timing of the first signal immediately before is included in the cycle. The period can be stored in the register N1.
After step S27 or S29 is executed, the process proceeds to step S30, where the second counter valid flag 2 is reset. In step S31, the second counter is initialized to 0, and then the input pulse period is counted again. In step S32, the calculation permission flag 2 is set, and this interrupt processing routine is terminated.
[0044]
As described above, the second counter valid flag stores in the register the time n2 (n1) until the generation timing of the first signal of the input pulse including the first signal in its cycle (step S20), the period until the period N2 (N1) of the input pulse is stored in the register (step S30) is set. As a result, for the input pulse including the generation timing of the first signal in its cycle, the time until the generation timing of the first signal and the cycle of the input pulse can be reliably stored in the register.
The sequential storage flags 1 and 2 are provided to store the count value of the second counter corresponding to the first first signal in the registers n1, n2 and N1, N2 at the start of operation. This flag is reset after that.
[0045]
Further, the calculation permission flag 1 is set at the timing at which the first signal is generated in the registers n1 and n2 in the first timer interrupt processing routine (FIG. 4) executed when the first signal is generated. It is set when the count value of the second counter, that is, data corresponding to the position of the first signal in the input pulse including the first signal in its cycle is stored in the register.
Still further, the calculation permission flag 2 indicates the count value of the second counter when the rising edge is detected when the second counter valid flag is set, that is, the first signal during the cycle. Is set when the period of the input pulse included in (and the period of the previous input pulse) is stored in the register N2 (and N1).
Then, the main routine determines that when the calculation permission flags 1 and 2 are both set, the equation (4) (when the cycle of the first signal is other than 1 second, the equation (5) ) (Step S7, FIG. 3), and the first calculation permission flags 1 and 2 are reset.
[0046]
Therefore, as shown in FIG. 6, the determination result of step S6 of the main routine becomes YES after the rising point of the first input pulse after time t1, and the first frequency calculation process (step S7) is executed. However, in this case, as described above, nt1 is stored in both the registers n1 and n2, and Nt1 is stored in both the registers N1 and N2. It becomes the count value f0 of 1 counter. When step S7 of the main routine is executed after the rising edge of the first input pulse after time t2, an accurate frequency can be obtained based on the equation (4).
[0047]
Thus, the present invention Flow meter Frequency measurement Part Accordingly, it is possible to calculate an accurate frequency to the decimal part for each period (first period) of the first signal. Therefore, it is possible to perform accurate frequency measurement in a short time without requiring a long time to perform highly accurate measurement.
Further, since the count values (n1, N1) of the second counter in the previous measurement cycle are used for calculating the frequency in the next measurement cycle, it is possible to perform frequency measurement with high calculation efficiency.
[0048]
Next, according to the present invention described above. Flow meter Frequency measurement method The Apply Shi The flow meter will be described. FIG. 7 illustrates the above-described present invention. Flow meter Frequency measurement method The Apply Shi It is a block diagram which shows an example of the basic composition of the flowmeter.
As shown in the figure, this flow meter is roughly classified into a sensor unit 11 that outputs a pulse signal having a frequency corresponding to the flow rate of the fluid, a function selection unit 12 for selecting the function of the flow meter, and various instructions. And a manual operation unit 13 for manually inputting various data, a reset signal output unit 14 for detecting a power on / off and outputting a reset signal, and whether or not the control unit 20 is operating normally. A watchdog timer unit 15 that determines and outputs an interrupt signal when an abnormality occurs, a voltage drop detection unit 16 that monitors a power supply voltage and outputs an interrupt signal when a drop in the power supply voltage is detected, and control of the entire flow meter A control unit 20 that performs various operations, a non-volatile storage unit 17 that stores various data, a display unit 30 that performs various displays such as a measured flow rate value, and an external device EXCT such as a centralized monitoring device. A signal output unit 40 for outputting the issue, is configured to include a power supply unit 45.
[0049]
Here, the control unit 20 includes a comparison unit 21 for performing various comparisons, a determination unit 22 for performing various determinations based on the comparison results in the comparison unit 21, an arithmetic unit 23 for performing various calculations, and a control. A memory composed of a control unit 24 for controlling the entire unit 20, a timer unit 25 used for generating various timer interrupts, a ROM, a RAM, etc. for storing control programs and various data And a unit 26. The control unit 20 is configured by a single chip microcomputer, for example.
[0050]
Further, the display unit 30 is lit when a data display unit 31 for displaying the measured flow rate value, a unit display unit 32 for displaying a unit of the flow rate displayed by the data display unit 31, a signal output to be described later, and the like. An output 1 display unit 33 and an output 2 display unit 34 to be controlled are provided. Note that when the flow rate display unit is fixed, the unit display unit 32 may not be provided.
[0051]
Further, the signal output unit 40 converts the measured flow rate value into a PWM (pulse width modulation) signal, and outputs it to the first data input terminal DIN1 of the external device EXCT such as a centralized monitoring device. −1, switch output 1 output unit 40-3 for outputting output 1 indicating that to the switch 1 input SW1 of the external device EXCT when the measured flow rate value is less than (or more than) the first predetermined value And a switch output 2 output unit 40-4 for outputting an output 2 indicating that to the switch 2 input SW2 of the external device EXCT when the measured flow rate value is equal to or greater than (or less than) a second predetermined value. I have.
In place of or in addition to the PWM signal output unit 40-1, as indicated by a broken line, an analog flow rate signal having a current range of 4 to 20 [mA] and corresponding to the measured flow rate value is centrally monitored. For example, a 4 to 20 mA transmission signal output unit 40-2 that outputs to an analog input terminal of the external device EXCT may be provided.
Reference numeral 45 denotes a power supply unit, which supplies, for example, DC 12-24 [V] power supplied from the external device EXCT to an operating voltage of the flowmeter. Moreover, you may make it use a battery as a power supply.
[0052]
An outline of the operation of the flow meter configured as described above will be described.
When the flow meter is activated, the control unit 24 first performs initial setting of the flow meter. Then, the setting state of the function selection unit 12 is read to determine the operation mode of the flow meter. Here, it is assumed that the instantaneous flow meter mode is set.
Next, various setting states such as the diameter and material of the flow path set by the function selection unit 12 and the version of the control program are displayed on the display unit 30, and the measured flow rate input from the sensor unit 11 is displayed. The measurement of the frequency of the pulse signal having the corresponding frequency is started.
[0053]
As described above, this measurement is performed by counting the number of pulses of the input signal according to the output of the first timer (1 second timer) and measuring the integer part of the frequency to be measured. And by measuring the output timing of the first timer with the reference clock having a period of 1 msec, the fractional part of the frequency to be measured is measured.
Then, using the comparison unit 21, the determination unit 22, and the arithmetic unit 23, the frequency is calculated based on the equation (4), and the instantaneous flow rate is calculated from the calculated frequency by the equation (2) or (3). calculate. Then, the calculated instantaneous flow rate value is displayed on the display unit 30 and is output from the signal output unit 40 to the external device EXCT. Then, the comparison unit 21 and the determination unit 22 compare the measured instantaneous flow rate with a preset flow rate value, and depending on the comparison result, the switch output unit 40-3 or 40-4. Supplies the switch output to the external device EXCT. Further, an integrated flow value obtained by integrating the calculated instantaneous flow value is calculated. The integrated flow rate value is displayed on the display unit 30 according to the operation of the manual operation unit 13.
[0054]
Next, the present invention Flow meter Frequency measurement method The Apply Shi A more specific embodiment of the flow meter (instantaneous flow meter) of the present invention will be described in detail. In this embodiment, it is assumed that a common control program is used for both flow meters so that this flow meter can be used as both an instantaneous flow meter and an integrated batch flow meter.
8A and 8B are views showing the structure of an embodiment of the flow meter, wherein FIG. 8A is a top view showing a display and operation panel surface, FIG. 8B is a sectional view showing an internal structure, and FIG. It is a side view which fractures | ruptures and shows. In this figure, the instantaneous flow meter is attached to the measuring unit main body 50 connected in the middle of the flow path through which the fluid whose flow rate is to be measured, and is mounted above the measuring unit main body 50 so as to be positioned every 90 °. It consists of a measurement display. Here, the measuring unit main body 50 is sized according to the pipe to which it is connected, and the measurement display unit can be commonly applied to the material and the diameter of many types (for example, 64 types) of piping. It is supposed to be possible. In other words, the measurement display section can be used in common for many models, and as described later, the diameter and material of the pipe can be selected and set by operating the manual operation section (key input section). It is made to be able to.
[0055]
The measuring unit main body 50 has an inlet connected to the upstream side and an outlet connected to the downstream side, and the generation frequency of the Karman vortex formed on the downstream side of the columnar object 51 placed in the flow has a wide Reynolds number. By utilizing the fact that it is proportional to the flow velocity, by measuring the frequency of occurrence of this vortex flow, it is configured as a Karman vortex flow type that can know the flow velocity or flow rate. This Karman vortex flow type has a simple structure with no sliding parts and is excellent in reliability and durability. In addition, there are vortex generators and vortex detectors in the fluid flow path. Is small, the pressure loss is small.
The measuring unit main body 50 is provided with a piezoelectric element 52 as a sensor inside the holder for detecting the pressure in the flow path that changes due to the generation of vortex. The piezoelectric element 52 outputs a flow rate signal consisting of an electrical signal that changes at a frequency equal to the frequency of eddy current generation, and supplies the flow rate signal to an electronic circuit provided in the measurement display unit via a lead wire.
[0056]
The measurement display unit includes a case 53 composed of an upper case 54 and a lower case 55 which are abutted via a waterproof packing, a first printed board (display board) 61 accommodated in the case 53, and a second printed board. (CPU board) 62, third printed circuit board (sensor board) 63, LEDs 33 and 34 arranged on the upper surface of the upper case 54, for example, a data display unit 31 constituted by a three-digit 7-segment LED display and operation keys 41, 42, 43, etc., and a hollow rotating shaft 56 fixed on the measuring unit main body 50 with a screw 59 is rotatably fitted through a waterproof packing in a hole formed in the bottom of the lower case 55. The measuring unit main body 50 can be adjusted so as to be positioned every 90 °. The lead wire from the piezoelectric element 52 is led to the electronic circuit formed on the sensor substrate 63 through the hollow portion of the rotating shaft 56. Reference numeral 60 denotes a signal line including a shield line for connecting to an external device.
[0057]
Further, the display substrate 61 and the CPU substrate 62 are attached to the upper case 54 with a mounting screw 58 through a metal spacer, and the sensor substrate 63 is attached to the lower case 55 with a mounting screw 58 through a metal spacer. It is attached. Here, the upper case 54 and the lower case 55 are made of, for example, a resin in which a conductive shield material is applied, and are provided at a position where the screw 58 and the metal spacer in the printed circuit boards 61 to 63 abut. The case 53 and the printed circuit boards 61 to 63 are electrically connected to each other through the formed metal part.
The upper case 54 is attached to the lower case 55 by a screw 57 so as to be freely opened and closed, and can be opened when performing various setting operations.
[0058]
In the example described above, an example in which two LEDs 33 and 34 and a three-digit seven-segment display 31 as the data display unit are provided on the upper case 54 as a display unit has been shown. It is not limited to. FIG. 9 is a diagram showing another example of the display unit. In the example shown in this figure, in addition to the LEDs 33 and 34 described above and the three-digit display 31, two LEDs 35 and a display unit are shown. 36 to the right of LED 35 ^Three “L” is displayed on the right side of the LED 36. Accordingly, in the example shown in FIG. 9, the LED 35 is turned on to indicate that the unit of numerical values displayed on the three-digit display 31 is cubic meters, and the LED 36 is turned on. By this, it can be shown that the unit of the numerical value displayed on the display 31 is liters. That is, in this example, the unit display unit 32 is constituted by the LEDs 35 and 36.
Further, the LED 33 and the LED 34 are point-controlled when the first output and the second output are output to the external device, as will be described later. The LED color may be changed such that a red LED is used as the LED 33 and a green LED is used as the LED 34.
[0059]
FIG. 10 is a diagram showing an example of the arrangement of circuit components on the three printed boards, that is, the display board 61, the CPU board 62, and the sensor board 63. As shown in FIG. In this figure, (a) is a view showing a state in which the printed boards 61 to 63 are assembled in the case 53, (b) is a surface view of the display board 61, and (c) is a view of the CPU board 62. FIG. 4D is a rear view, FIG. 4D is a front view of the sensor substrate 63, and FIG. 4E is a rear view of the sensor substrate 63.
As shown in FIG. 10A, the display substrate 61 and the CPU substrate 62 are electrically connected via a connector 64, and the CPU substrate 62 and the sensor substrate 63 are electrically connected via a flat cable 65. Connected. A microcomputer 20 that operates as the control unit is provided on the CPU board 62, and an EEPROM that operates as the nonvolatile memory element 17 is provided on the back surface thereof.
Further, as shown in FIG. 10B, an inspection mode setting pin 18 composed of two pins is provided on the surface of the display substrate 61. By short-circuiting the inspection mode setting pin 18, An inspection mode to be described later can be set.
[0060]
Further, as shown in FIG. 5C, on the back surface of the CPU board 62, function selection pins including two sets of jumper pins J1 and J2 constituting the function selection unit 12 are provided. Jumper pin J1 is used to select whether to operate this flow meter as an instantaneous flow meter or an integrated batch flow meter. When jumper pin J1 is short-circuited by a jumper wire, it operates as an instantaneous flow meter. When it is open, it is set to operate as an integrating batch flow meter. The jumper pin J2 is used to select whether the measurement data from the flowmeter is transmitted to an external device by a 4 to 20 mA transmission method or a PWM modulated signal, and is short-circuited by a jumper wire. Sometimes the measurement flow rate data is transmitted by a 4 to 20 mA transmission method, and when it is opened, the PWM modulation signal is transmitted to an external device.
[0061]
As shown in FIG. 10 (d), terminals S + and S− to which lead wires from the piezoelectric element 52 are connected are provided on the surface of the sensor substrate 63, and an adjustment trimmer VR, Various electronic components such as various operational amplifiers, diodes, varistors and capacitors are arranged. Reference numeral 66 denotes a terminal to which a connection cable 60 to the external device is connected. Further, as shown in FIG. 5E, on the back surface of the sensor substrate 63, various output transistors such as a PWM output transistor 76 described later, a three-terminal stabilized power circuit 78 that operates as the power supply unit 45, and the like. Various electronic components are provided.
[0062]
An example of the circuit configuration of this flow meter will be described with reference to the block diagrams of FIGS.
In FIG. 11, reference numeral 20 denotes a microcomputer that controls the entire flow meter, and includes a first counter (main counter) 81, a second counter (sub counter) 82, and a plurality of timers 1 to n. For driving a timer register group 83 composed of timers, a ROM 84 for storing a control program and a calculation coefficient table (to be described later), a RAM 85 used as a data area and work area for storing various data, and a display unit 30 A display driver and a PWM output function unit for outputting a PWM signal from the output port are mounted. The PWM output function unit has, for example, a 10-bit resolution, and includes a PWM prescaler that sets a PWM cycle, a PWM register that sets an “H” level period of an output pulse, and the like.
The timer register group 83 includes a first period timer (1 second timer) corresponding to the first timer, a timer generating a 1 msec reference clock, a second period timer (0.2 second timer), and the like. It is included. Here, the second period timer outputs a signal having a second period synchronized with the output signal of the first period timer and having the output signal period of the first period timer divided by the measurement lower limit frequency. In this example, the signal has a period of 0.2 seconds obtained by dividing the period of 1 second of the output of the first timer by the measurement lower limit frequency of 5 Hz. As will be described later, the timing of the calculation operation of the calculation unit is controlled in accordance with the output signal of the second period timer.
The first cycle timer and the second cycle timer may be provided separately, but here, the first cycle timer output is obtained based on the output of the second cycle timer. For example, the output of the second period timer may be counted, and the first period timer output may be output every time 5 is counted.
Further, the main counter 81 and the sub counter 82 are connected to an input port (count signal input port) to which an input signal from the sensor unit 11 is applied, and the main counter 81 is 1 second (first cycle). The sub-counter 82 measures the period of the input pulse in units of 1 msec.
[0063]
Reference numeral 11 denotes a sensor unit including the piezoelectric element 52, an amplifier 67 that amplifies an electric signal from the piezoelectric element 52, and a waveform shaping circuit 68 that shapes the output signal of the amplifier 67 and outputs it as a pulse signal. The output β of the sensor unit 11 is input to the count signal input port of the microcomputer 20. Further, the output β of the sensor unit 11 is also applied to the signal output unit shown in FIG. 12 so that it can be directly output to an external device EXCT such as an adjustment inspection device via the output transistor 77. Has been made.
Reference numeral 12 denotes a function selection unit which, as described above, transmits the jumper pin J1 for selecting whether to operate as an instantaneous flow meter or an integrated batch flow meter, and the measurement output to an external device by a 4 to 20 mA transmission signal. Alternatively, a jumper pin J2 for selecting whether to output to an external device by a PWM (Pulse Width Modulation) signal is provided. The outputs of the jumper pins J1 and J2 are connected to the input port of the microcomputer 20.
Reference numeral 18 denotes an inspection mode setting pin. As described above, this flow meter can be set to the inspection mode by short-circuiting the inspection mode setting pin 18. At the time of inspection before shipment from the factory, the inspection mode setting pin 18 sets the inspection mode, and as will be described later, an adjustment inspection apparatus is connected as the external apparatus EXCT to execute inspection. The output of the inspection mode setting pin 18 is connected to the input port of the microcomputer 20.
[0064]
Reference numeral 13 denotes a manual operation unit (key input unit), which is provided with three operation keys, a setting key (ENT key) 41, an up key (Δ key) 42, and a down key (▽ key) 43, as described above. Each is connected to an input port of the microcomputer 20.
A watchdog timer 15 inputs an interrupt signal to the microcomputer 20 when a signal from the output port of the microcomputer 20 is not input for a predetermined time. With this interrupt input, the microcomputer 20 starts a second start process described later. The scheduled output to the watchdog timer is executed by, for example, a timer interrupt processing routine that is executed every predetermined period.
Further, reference numeral 14 denotes a power-on reset circuit, which detects when a power supply voltage Vcc is applied and applies a pulse signal to the reset terminal of the microcomputer 20. As a result, the microcomputer 20 executes a first start process described later.
[0065]
Reference numeral 30 denotes the display unit, as shown in the figure, a 3-digit 7-segment LED display 31 as a data display unit, a first output OUT1 (or an output signal OUT when used as an integrating batch flow meter). OUT1 LED 33 that is lit at the time of output, OUT2 (IN) LED 34 that is lit at the time of output (input) of the second output OUT2 (when used as an integrating batch flow meter), drive digit selection circuit 37, and An LED drive circuit 38 is provided. In the case of the embodiment having the unit display unit 32 shown in FIG. 9, the numerical value in the three-digit display 31 is m. ^Three There are further provided an LED 35 for indicating a numerical value in units of (cubic meters) and an LED 36 for indicating a numerical value in units of L (liters). Then, data for performing the display is output from the display drive circuit built in the microcomputer 20 to the drive digit selection circuit 37 and the LED drive circuit 38 via the output port, and a desired display can be performed. It has been made possible.
Although an example in which an LED is used as a display element is shown here, the present invention is not limited to this, and other display elements such as a liquid crystal (LCD) can be adopted.
Further, the number of digits of the display 31 is not limited to three digits, and may be any number of digits such as eight digits.
[0066]
Reference numeral 17 denotes an EEPROM (Electrically Erasable Programmable ROM) which is a non-volatile memory element, which stores integrated flow rate value data, various set values, and primary slope data and intercept data corrected at the time of adjustment inspection described later. As a result, it is possible to prevent data loss when the power supply voltage drops.
Reference numeral 69 denotes a large-capacitance capacitor connected in parallel to the power supply terminal, and is used for backup when the power supply voltage is temporarily lowered.
Furthermore, reference numeral 16 denotes a voltage detector that monitors the power supply voltage and performs a power supply voltage check interrupt when the voltage drops below a predetermined voltage.
[0067]
The first output OUT1 and the second output OUT2 are supplied from the output port of the microcomputer 20 to the signal output unit 40 shown in FIG. Here, the first output OUT1 is a signal output when the measured instantaneous flow rate value becomes lower than the first set flow rate value (for example, the lower limit flow rate value) QL, and the second output OUT2 is measured. This is a signal that is output when the instantaneous flow rate value that has been increased exceeds the second set flow rate value (for example, the upper limit flow rate value) QU. As described above, by outputting the first output OUT1 and the second output OUT2 to the external device without delay, it is possible to quickly control the external device.
When this flow meter is used as an integrated batch flow meter, the first output OUT1 is an output OUT, and instead of the second output OUT2, as shown by a dotted line, the signal output unit 40 / The input IN from the external device EXCT is input to the input port of the microcomputer 20 via the power supply unit 45, but further explanation is omitted here.
[0068]
In FIG. 12, reference numeral 70 denotes an output transistor to which the first output OUT1 as the first comparison result is applied to the gate, and reference numeral 71 denotes the second output OUT2 as the second comparison result to the gate. Output transistor. The drains of these output transistors 70 and 71 are output from the corresponding output terminals to an external device. Thereby, on the external device side, it is possible to perform rapid switch control using the OUT1 output and the OUT2 output. As shown in the figure, a protective Zener diode ZD is connected between each output terminal and the ground.
As described above, when the integrated batch flow meter is used, the input signal IN from the external device EXCT is shaped by the threshold circuit 72 and input. A protective resistor R and a protective diode D are connected between the input signal IN and the threshold circuit 72.
[0069]
Further, in the above, the output transistors 70 and 71 are provided corresponding to the first comparison result output OUT1 and the second comparison result output OUT2, respectively, but are described as another example in the lower part of FIG. As described above, the first output OUT1 and the second output OUT2 may be input to the OR circuit OR to obtain a logical sum, and the conduction / non-conduction of the transistor 70 may be controlled by the logical sum output. In this case, a large number of comparison results can be output with a small number of output transistors. However, on the external device side, it is necessary to determine whether the output transistor is turned on or off based on the first or second comparison result from the measured output data. Three or more types of comparison results may be output.
[0070]
Further, 10-bit measurement output data is supplied to the signal output unit 40 from an output port of the microcomputer 20 with an output latch. The 10-bit measurement data is input to the digital analog (D / A) conversion unit 73 in the signal output unit 40 shown in FIG. 12, and is supplied to the inspection signal output terminal to which the adjustment inspection apparatus is connected in the inspection mode. Is done. The measurement data converted into an analog signal by the 10-bit D / A converter 73 is input to a 4 to 20 mA transmission signal output unit 75 via a voltage / current converter (V / I converter) 74, and This is output to the external device EXCT as a 20 mA transmission signal. As shown in the figure, a capacitor C and a varistor V are connected in parallel between the output of the 4-20 mA transmission signal output unit 75 and the ground so as to absorb noise and surge.
[0071]
Furthermore, the PWM signal having the 10-bit resolution described above corresponding to the flow rate value measured from the output port of the microcomputer 20 is output, and the PWM signal is applied to the gate of the output transistor 76 shown in FIG. It is output to the external device EXCT via the PWM output terminal. A protective Zener diode ZD is connected between the PWM output terminal and the ground.
As described above, in the present invention, the 4 to 20 mA transmission signal or the PWM signal corresponding to the measured flow rate value is generated based on the measurement data having a 10-bit resolution, so that error propagation is performed. It is possible to output a signal having no error to an external device.
[0072]
Further, the measured pulse signal β from the waveform shaping unit 68 of the sensor unit 11 is applied to the gate of the output transistor 77 of the signal output unit 40, and the drain of the transistor 77 is used for testing the signal output unit 40. Via the signal output terminal, it is connected to the adjustment inspection apparatus connected in the inspection mode.
In FIG. 12, a MOS transistor is used as each output transistor, but a bipolar transistor may be used. In this case, the outputs OUT1 and OUT2 are respectively applied to the bases of the bipolar transistors, and their collectors are connected to the output terminals.
Reference numeral 78 denotes a DC stabilized power supply circuit. In this embodiment, a DC voltage of 12 to 24 V supplied from the external device EXCT is input, converted into a drive voltage for the flowmeter, and output. As shown in FIG. 12, a surge preventing varistor V and a noise removing capacitor C are connected in parallel between the power supply lines (+ DC, −DC and GND) supplied from the external device. Has been. Further, the diode D inserted between the power supply line + DC and the direct current stabilizing power supply 78 prevents damage to the circuit against reverse connection of the polarity of the power supply line.
[0073]
Various data stored in the ROM 84, the RAM 85, and the EEPROM 17 will be described.
FIG. 13A shows an example of a memory map of the ROM 84 and RAM 85. FIG. As shown in this figure, in the area of the RAM 85, various register areas, areas for storing correction coefficients and various flags to be described later, work areas, areas for storing integrated flow value data, and integrated batch flow values are stored. An area to be used is provided.
In the area of the ROM 84, a control program, an aperture setting data table, an interrupt vector, and the like are stored. Here, the diameter setting data table is coefficient data (inclination data ai and intercept data bi in the equation (2)) corresponding to the diameter and material of the pipe, for example, for 64 types of models (bore diameter and material). Corresponding data is stored.
[0074]
FIG. 13B is a diagram for explaining the configuration of the aperture setting data table. As shown in this figure, the aperture setting data table has a 4-page configuration in which 16 types of setting data are used as one page. As shown in the figure, each setting data includes a setting code (model setting code) for identifying the setting data, a code for specifying the diameter, a material code for specifying the main body material, a flow frequency f1 to 110 of the rated flow rate. Frequency data f1 to f6 that divide up to a frequency f6 corresponding to an instantaneous flow rate value of 5% into five sections, and linear gradient data a1 to a5 when a function of frequency and flow rate is approximated by a broken line corresponding to the five sections. And intercept data b1 to b5 are stored. The flow frequency f1 is a measurement lower limit frequency determined by the model, that is, the diameter and material of the measuring unit main body 50 (FIG. 8), and has a value of about 5 Hz, for example.
Note that the data a1 to a5 and b1 to b5 are average values of instrumental error dispersion, and even if the flow rate is calculated using this data as it is, a highly accurate measurement result cannot be expected. Therefore, also in the present invention, primary inclination data A1 to A5 and primary intercept data B1 to B5 (hereinafter collectively referred to as “correction coefficient”) corrected for each unit in the adjustment inspection process described later. The flow rate is calculated using this correction coefficient as shown in the equation (3). Thereby, it is possible to perform very accurate measurement.
[0075]
FIG. 13C shows an example of a memory map of the EEPROM 17. As shown in this figure, the EEPROM 17 includes an inspection end flag, the corrected primary equation inclination data A1 to A5, the corrected primary equation intercept data B1 to B5, integrated flow data, integrated batch flow value data, model Setting code determination data, integration display method determination data, batch flow value setting data, upper limit flow value setting data, lower limit flow value setting data, and switch output cycle determination data are stored. Note that details of these data will be described in corresponding portions in a flowchart described later.
[0076]
Next, the operation of this flow meter (instantaneous flow meter) will be described in detail. As described above, this flow meter can operate as both an instantaneous flow meter and an integrated batch flow meter. Here, a case where the flow meter is operated as an instantaneous flow meter will be described.
This flow meter is generally operated by three types of interrupt processing: a main routine as a flow meter, frequency measurement interrupt processing, 1 msec clock counting interrupt processing, and power supply voltage check interrupt processing. .
Here, by the frequency measurement interrupt process and the 1 msec clock count interrupt process, Flow meter The processing related to the measurement of the integer part of the frequency of the signal under measurement by the main counter and the measurement of the fractional part by the sub-counter according to the frequency measurement method is executed, and the above-described equation (4) or (5) is executed by the main routine. Various processes such as calculation of the frequency using, calculation and display of the instantaneous flow rate value based on the frequency, output to an external device, and output of a switch output signal are executed.
[0077]
FIG. 14 is a diagram showing a processing flow of the main routine. As shown in this figure, the main routine has two start positions, a first start (start 1) and a second start (start 2). Here, when a reset signal is input from the power-on reset circuit 14, the operation starts from the start 1, and when an interrupt is input from the watchdog timer 15, the operation starts from the start 2. .
[0078]
When the supply of power from the DC stabilized power supply circuit 78 is started by connecting the external device EXCT and the flow meter, the power-on reset circuit 14 detects this, and the microcomputer 20 A power-on reset pulse is applied to. Thereby, the process is started from start 1, and first, the first initialization process of step S41 is executed. In the first initialization process based on the power-on reset, a predetermined initialization process of the instantaneous flowmeter is executed and all the contents of the RAM 85 are reset. In step S42, the timer operation of each timer in the timer group 83 is started. However, the operation of the timer that generates the second period timer (0.2 second timer) and the 1 msec reference clock is not started here. Therefore, the signal from the first period timer is not output as described above.
Subsequently, the inspection end flag, integrated flow rate data, integrated batch flow rate value data, and the like are read from the EEPROM 17 and stored in a predetermined area of the RAM 85 (step S43). In the initial state, that is, in the state where the adjustment inspection device is connected as the external device EXCT before shipment from the factory, both the inspection end flag and the two accumulated data are set to the initial value 0. Next, the first output OUT1 (OUT) is turned on for 2 seconds (step S44). As a result, the external device EXCT (adjustment inspection device) can be notified of the start (start 1) of the instantaneous flowmeter by power-on reset. At the same time, the OUT1 LED 33 is also lit for 2 seconds.
[0079]
On the other hand, an interrupt signal is input from the watchdog timer 15 when a fixed time signal is not output to the watchdog timer 15 within a predetermined period due to some reason such as a runaway control program. At this time, the process starts from the start 2, and the second initialization process of step S45 is executed. In the second initialization process, a predetermined initialization process of the instantaneous flowmeter is executed. Unlike the first initialization process, a correction coefficient and an integrated flow value stored in the RAM 85 are used. Data and accumulated batch data are not cleared. Then, in the same manner as in step S42, the timer operation of each timer excluding the second period timer (0.2 second timer) and the 1 msec reference clock is started (step S46).
[0080]
After step S44 or step S46 is executed, the process proceeds to step S47, where it is determined whether or not the 4 to 20 mA transmission system is set by the jumper pin J2 in the function selection unit 12. If the result of this determination is YES, the process proceeds to step S48, where the D / A converter 73, V / I converter 74 and 4-20 mA transmission signal output unit 75 of the signal output unit 40 can be operated, and the external The output is set to 4 to 20 mA transmission system. If the determination result in step S47 is NO, the process proceeds to step S49, the PWM output function unit built in the microcomputer 20 is set to be operable, and measurement data is output to the outside by the PWM method. Set to.
[0081]
Next, it progresses to step S50 and it is determined whether the said jumper pin J1 is set to the instantaneous flow meter mode. When the jumper pin J1 is short-circuited and the instantaneous flow meter mode is set, the determination result is YES and the instantaneous flow meter processing program in step S51 is executed. On the other hand, when the jumper pin J1 is opened, the integrated batch flow meter processing program in step S52 is executed. In this specification, since the instantaneous flow meter is targeted, the instantaneous flow meter processing program (step S51) when the determination result in step S50 is YES will be described in detail below.
[0082]
FIG. 15 is a flowchart for explaining the operation of the instantaneous flow meter processing program in step S51.
When this instantaneous flow meter processing program is started, first, in step S60, the second output OUT2 is validated and the input IN is invalidated.
Next, it progresses to step S61 and it is determined whether the test | inspection completion flag is set. This inspection end flag is a flag that is set when this instantaneous flowmeter inspection and coefficient data correction processing are performed in the adjustment inspection process described later. In the initial state, this inspection end flag is set. The determination result in step S61 is NO. At this time, the process proceeds to step S62, and the model setting code of the instantaneous flowmeter is set using the manual operation unit 13, that is, the setting key 41, the up key 42, and the down key 43. Thereby, the diameter and material of the flow path in which this instantaneous flow meter is used are set. As described above, this step S62 is executed when the inspection end flag is not set, and is actually executed by the manufacturer.
[0083]
On the other hand, when the examination end flag is set, the process proceeds to step S63, and various data (such as the corrected primary slope data A1 to A5 and the primary intercept data B1 to B5) stored in the EEPROM 17 are read. And stored in a predetermined area of the RAM 85.
When the adjustment inspection process is not performed, standard primary slope data a1 to a5 and primary intercept data b1 to b5 stored in the ROM 84 are used for the above-described flow rate calculation. Become.
[0084]
After step S62 or step S63 is executed, the process proceeds to step S64, and based on the setting code and information read from the EEPROM 17, the diameter and material of the flow path and version information of the control program are displayed on the display unit. 30 are sequentially displayed for a predetermined time.
FIG. 16 shows an example of the display form of the display unit 30 in step S64. In FIG. 16, (a) shows an example of a caliber display form, (b) shows an example of a material display form, (c) shows an example of a software version display, and (a) → (b) Display is sequentially repeated for a predetermined time (for example, 1 second) in the order of (c) → (a).
[0085]
Here, as the diameter, there are a display in millimeters (mm) (A is added after the number) and an indication in inches (B is added after the number). Therefore, these apertures are displayed using the 3-digit data display 31 in the form shown on the right side of FIG. In the example shown in FIG. 16A, “10A” is displayed. Note that small, medium, and large described on the left of each aperture in FIG. 16 (a) indicate the classification to which each aperture belongs when each aperture is classified into three types: large, medium, and small. ing.
Examples of the material include L-PPS, PPS (polyphenylene sulfide), PVC (polyvinyl chloride), PFA, SUS (stainless steel), and the like, in the form shown in FIG. It is displayed on the display 31. In the illustrated example, the material is PVC.
Further, FIG. 16C shows a display example of the version of the control program. In this example, it is shown that the version of the control program is V3.8.
As described above, in the instantaneous flow meter of the present invention, the version of the control program is displayed on the display 31 that displays the measurement data at the start of operation, which is very convenient when performing maintenance or the like. ing.
[0086]
Now, after displaying the caliber, material, and program version (step S64), the process proceeds to step S65, and the time measurement process of the 0.2 second timer and the 1 msec clock is started. The counting process of the sub counters is started. Then, 0 is set in a register j that stores a value j indicating where in the second the 0.2 second interrupt is located. The contents of this register j indicate the position of the second signal having a period of 0.2 seconds in the 1-second period of the first signal, and the first signal (1-second timer) ) At the same timing, j = 1, and then sequentially counted as 2, 3, and 4. When j = 5, j = 0 is converted, and j = 1, 2, 3,. Is done.
As described above, in this embodiment, the output of the first cycle timer is generated from the output of the second cycle timer (0.2 second timer), but the first cycle timer (1 second timer) ) And a second period timer (0.2 second timer) may be provided separately to generate the first signal and the second signal.
[0087]
In step S66, it is determined whether or not the inspection mode is set. This determination is performed by inputting a signal from the input port to which the inspection mode setting pin 18 is connected and determining whether or not the inspection mode setting pin 18 is short-circuited. When the inspection mode setting pin 18 is short-circuited and set to the inspection mode, the process proceeds to step S67 to determine whether or not the inspection end flag is set. When the inspection end flag is not set, an inspection process in step S68 described later is executed, and thereafter a flow rate calculation process in step S69 is executed.
On the other hand, when the inspection mode is not set, or when the determination result of step S67 is YES, the flow proceeds to the flow rate calculation process of step S69. Thereafter, the display process in step S70, the external output process in step S71, the switch output process in step S72, and the key input process in step S73 are sequentially executed. Then, after the key input process in step S73 is executed, the process returns to step S66 again, and the processes in steps S66 to S73 are repeatedly executed. The details of each processing in steps S69 to S73 will be described later.
The above is the outline of the instantaneous flow meter processing program.
[0088]
FIG. 17 is a flowchart for explaining the operation of the power supply voltage check interrupt process. The voltage detector 16 determines whether or not the power supply voltage Vcc is equal to or higher than a predetermined voltage, and when detecting that the power supply voltage Vcc is lower than the first predetermined voltage, the voltage detector 16 supplies power to the microcomputer 20. Generate a voltage check interrupt. Thereby, the power supply voltage check interrupt process is started. When the power supply voltage check interrupt process is started, first, in step S81, the accumulated data in the RAM 85, the diameter and material data, the data specifying the accumulated display method, the upper limit flow value setting data, the lower limit flow rate Value setting data and selected predetermined data such as the switch output cycle determination data are stored in the EEPROM 17. Thereby, loss of these data can be prevented.
[0089]
After the necessary data is saved in the EEPROM 17 in the step S81, the microcomputer 20 is put into a wait state (step S82). When the power supply voltage Vcc returns to the first predetermined voltage or higher again without reaching the second predetermined voltage lower than the first predetermined voltage, the wait state is canceled (step S83), and again Return to main routine processing. In this case, since the power supply voltage Vcc has not dropped below the second predetermined voltage, it is considered that the data in the RAM 85 has not been lost, and the processing returns to the main routine.
On the other hand, when the power supply voltage Vcc drops below the second predetermined voltage, it is considered that the data in the RAM 85 has been lost. Therefore, when the power supply voltage Vcc returns, the power-on reset circuit 14 operates. Then, the process is started again from the first start position (main routine in FIG. 14).
[0090]
Next, the adjustment inspection process in step S68 (FIG. 15) will be described with reference to the connection diagram in the adjustment inspection process shown in FIG. 18 and the flowchart of FIG.
As shown in FIG. 18, this adjustment inspection process is executed in a state where the adjustment inspection apparatus is connected as the external apparatus EXCT. As shown in FIG. 11 and FIG. 12, the signal output unit 40 / power supply unit 45 is connected to the adjustment inspection apparatus EXCT which is an external device in this case. The offset adjustment and span adjustment of the signal corresponding to the instantaneous flow rate of the ˜20 mA transmission signal or the PWM signal are omitted in FIG.
[0091]
In FIG. 18, a high-precision reference flow meter 101 serving as a reference, a metering unit main body 50 of the instantaneous flow meter of the present invention, a pump 102, and a flow control valve 103 are attached to a pipe 100. Then, as described above, the OUT1 output of the output transistor 70 in the signal output unit 40, the 10-bit measurement data output, and the output of the sensor unit 11 via the output transistor 77 are input to the adjustment inspection device via a connector. Has been. Further, the output of the high-accuracy reference flow meter 101 is also input to the adjustment inspection apparatus. And the control signal with respect to the said flow control valve 103 is output from the said adjustment test | inspection apparatus, and it controls so that a predetermined | prescribed flow volume may be sent through the said piping 100 according to the predetermined test | inspection step shown in FIG.
As shown in FIG. 11, a power supply line, an input signal line, and an output signal line are actually connected, but the description is omitted in FIG.
[0092]
The adjustment inspection step S68 is performed in such a connected state. As shown in the flowchart of FIG. 19, first, in step S91, each part of the flowmeter is inspected according to a predetermined procedure. Next, proceeding to step S92, the output OUT1 is turned on for a predetermined time (for example, 0.1 second) and then turned off, and the first step of the adjustment inspection process is started for the adjustment inspection apparatus. Is notified. In response to this, the adjustment inspection apparatus uses the high-accuracy reference flowmeters to obtain the reference flow rates Q1 to Q6 corresponding to the six frequencies f1 to f6 stored in the ROM 84 corresponding to the selected model (model). While measuring at 101, the flow control valve 103 is controlled to flow through the pipe. Here, first, the flow rate control valve 103 is controlled such that the first reference flow rate Q1 flows through the pipe 100. The flow meter calculates and stores the frequency by the above-described method based on the input signal from the sensor unit 11 at this time (step S93). The frequency at this time is F1. And while displaying this frequency F1 and the flow volume Q1 at that time on the said indicator 31, this frequency value F1 is output to the said adjustment inspection apparatus via the said signal output part 40 (step S94).
[0093]
Next, the process proceeds to step S95, where the output OUT1 is turned on again for a predetermined time to notify the adjustment inspection apparatus of the progress of the step. As a result, the adjustment inspection device controls the second reference flow rate Q2 to flow through the pipe 100. And the said control part 20 calculates and memorize | stores the frequency F2 based on the input from the sensor part 11 at that time (step S96), while displaying the measured frequency value F2 and the reference | standard flow volume Q2, and also to the said adjustment inspection apparatus. Output (step S97). Then, the process proceeds to step S98, and the corrected primary slope data A1 and intercept data corrected based on the measured frequency F1 at the reference flow rate Q1 stored in step S93 and the measured frequency F2 at the reference flow rate Q2 stored in step S96. B1 is calculated. The correction coefficients A1 and B1 are calculated based on the following expressions (6) and (7).
A1 = (Q2-Q1) / (F2-F1) (6)
B1 = (Q1 * F2-Q2 * F1) / (F2-F1) (7)
The calculated correction coefficients A1 and B1 are stored in a predetermined area of the RAM 85. In step S99, the output OUT1 is turned on for a predetermined period to notify the adjustment inspection apparatus that the process in this step has been completed.
[0094]
Thereafter, in the same manner as described above, the reference flow rates Q3 to Q6 are sequentially flowed, and the correction coefficients A2 to A5 and B2 to B5 are similarly calculated using the measured frequency values F3 to F6 at that time and stored in the RAM 85. To do. In step S101, the display unit 31 displays the end of the inspection process. In step S102, the coefficients A1 to A5 and B1 to B5 stored in the RAM 85 are stored in the EEPROM 17. In step S103, the inspection end flag is set. The inspection process is completed after setting.
In steps S94, S97, etc., the frequency data F1 to F6 output to the adjustment inspection apparatus are stored as inspection records in the adjustment inspection apparatus. In steps S94, S97, etc., the measured frequency value Fi and the reference flow rate Qi are alternately blinked and displayed on the display 31 every predetermined period (for example, 0.5 seconds).
[0095]
Next, the frequency measurement interrupt process and the 1 msec clock count interrupt process will be described with reference to the flowcharts of FIGS. 20 and 21 and the time chart of FIG.
FIG. 20 is a flowchart of the frequency measurement interrupt process. This frequency measurement interrupt process is started by the output of the second period timer (0.2 second timer) generated every 0.2 seconds. When this process is started, first, in step S111, the 0.2 second timer is restarted. This ensures an accurate interrupt every 0.2 seconds each time. Further, as described above, in this embodiment, since the first period timer output is generated based on the output of the 0.2 second timer, the accuracy of the first period timer (1 second timer) output is increased. Is also guaranteed.
[0096]
In step S112, the switch output cycle determination data is referenced to determine whether the switch output is set at high speed. As described above, depending on the mode of use of this instantaneous flow meter, when the measured flow rate value exceeds a preset lower limit flow rate value or upper limit flow rate value, a high-speed (for example, within 1 second) switch output May be required. In order to cope with this, in the present invention, it is possible to select whether or not to make the switch output high-speed by the switch output cycle determination data. The switch output cycle determination data can be set by the user using the key switches 41 to 43 of the manual operation unit 13 in the key input processing routine (step S73) described in detail later. ing.
If the result of determination in step S112 is that high speed output has been made, a switch output flag is set in step S113, and the flow proceeds to step S114. On the other hand, when the high-speed output is not set, the process directly proceeds to step S114.
[0097]
In step S114, it is determined whether the content of the register j is 0-4. If j = 0 and j = 4, the process proceeds to step S119 as it is. When j = 1, the count content f0 of the main counter 81 is stored in the register in step S115, the count content of the main counter 81 is reset to 0 in step S116, and the count of the input pulse signal by the main counter 81 is performed again. Is resumed, and the process proceeds to step S119.
Thereby, as shown in FIG. 22, when j = 1, that is, at the measurement start (end) point of the first period timer, the count value f0 of the main counter is stored in the register. Therefore, the register stores the number f0 of input signal pulses input per second, that is, the integer part of the frequency of the input signal pulse.
When j = 2, the calculation permission flag 1 is set in step S117, and the process proceeds to step S119. Further, when j = 3, in step S118, an external output permission flag is set, and the process proceeds to step S119.
[0098]
As described above, when j = 0 or 4 in step S114, or after step S116, S117 or S118 is executed, step S119 is executed, and the contents of the register j are incremented. In step S120, it is determined whether or not the content of the register j is 2. When j = 2, the process proceeds to step S121. As will be described later, the sub-counter 82 counts the 1 msec reference clock from the rising edge to the falling edge of the input pulse from the sensor unit 11, and in this step S121, the count value n1 of the sub-counter 82 at this time point Is stored in a register. Then, the calculation permission flag 2 is set (step S122), and the current frequency measurement interrupt process is terminated.
That is, as shown in FIG. 22, in step S121, the time n1 counted by the 1 msec reference clock from the rising edge of the input pulse signal immediately before the measurement start (end) point to the measurement start point is obtained in the register. It is done.
On the other hand, if the decision result in the step S120 is NO, the process advances to a step S123 to judge whether j = 5. When j = 5, the contents of the register j are set to 0. When j ≠ 5, the frequency measurement interrupt process is terminated as it is.
[0099]
FIG. 21 is a flowchart for explaining the 1 msec clock counting interrupt process.
When the rising edge of the input pulse signal is detected, the 1 msec clock counting interrupt process is started (step S131), and the counting of 1 msec clock is started (step S132). Actually, this counting process is executed in the sub-counter 82. Then, it is determined whether or not the count value N1 is 200 or more (that is, 1 msec × 200 = 0.2 sec or more) (step S133), and when it is 200 or more, the second counter is reset. Then, detection of the rising edge of the next input pulse signal is awaited (step S139). As described above, in this example, the measurement lower limit frequency is set to 5 Hz, and when the cycle of the input pulse is 0.2 sec or more, the measurement lower limit frequency is equal to or lower than the measurement lower limit frequency. I'm waiting. In other words, if the frequency with flow is 5 Hz, there is no flow to be measured, so no pulse is input, and there is also a realistic aspect that there is no need to measure this input pulse.
[0100]
On the other hand, when the determination result of step S133 is NO, the process proceeds to step S134, and the above counting is repeated until the next rising edge is detected (NO in step S134). When the next rising edge is detected, the count value N1 of the sub-counter 82 so far is stored in a predetermined area of the RAM 85 (step S135). That is, as shown in FIG. 22, the period of the input pulse is sequentially measured by a 1 msec clock, and the measured value is sequentially stored in the RAM 85. At this time, the current count value is stored in an area of the RAM 85 different from the previous count value. That is, as an area for storing the count value N1 of the sub-counter 82 of the RAM 85, for example, an area for storing at least three count values is prepared, and the immediately preceding three count values N1 are sequentially stored.
[0101]
In step S136, it is determined whether the count value N1 stored in the RAM 85 is 20 or 16 in succession. This is to prevent erroneous measurement due to an induced voltage of the AC power supply (50 Hz or 60 Hz) mixed in the measurement signal as noise. If the decision result in the step S136 is YES, the process advances to a step S140 so as to reset the count value f0 of the main counter to 0 and the main counter 81 until the next count start time, that is, when j = 0. The counting operation is stopped.
In general, the flow value fluctuates finely, and usually the same frequency is not continuously detected. Therefore, it is possible to prevent the induction noise from the commercial AC power source from being detected by such a method.
[0102]
On the other hand, if the decision result in the step S136 is NO, the process advances to a step S137 to determine whether or not the calculation permission flag 2 is set. If the result of this determination is NO, the process returns to step S132, and the above-described measurement of the period of the input pulse signal is continued. On the other hand, if the calculation permission flag 2 is set and the determination result in step S137 is YES, the process proceeds to step S137, and the count value N1 at this time is read from the RAM 85 and stored in the register. Then, the processing after step S132 is repeated again. That is, as described above, the calculation permission flag 2 is set at a timing corresponding to j = 1 (step S122 in the frequency measurement interrupt process), and as shown in FIG. When the input pulse rises, the count value N1 is stored in the register. As a result, the cycle N1 of the input pulse signal straddling the time point j = 1 can be obtained in the register by the 1 msec clock counting interrupt process.
[0103]
As described above, the count contents f0 of the main counter 81 and the count contents n1 and N1 of the sub-counter 82 are written in the register by the frequency measurement interrupt process and the 1 msec clock count interrupt process. In the processing after the flow rate calculation processing step S69 (FIG. 15), a flow rate value is calculated using these count values, displayed, output to the outside, and further a switch output to the outside is performed.
Hereinafter, these processes will be described in detail.
[0104]
FIG. 23 is a flowchart showing the flow rate calculation processing in step S69. When this process is started, first, it is determined whether or not both the calculation permission flag 1 and the calculation permission flag 2 are set (step S141). Here, when the calculation permission flags 1 and 2 are not set, the count value f0 of the main counter and the count values N1 and n1 of the sub-counter are not prepared in the register, and the instantaneous flow rate value and the integrated flow rate value are not prepared. Since it is not the timing to execute this calculation, the flow rate calculation process is terminated as it is.
[0105]
On the other hand, when both the calculation permission flag 1 and the calculation permission flag 2 are set (when j = 2 or later as shown in FIG. 22), the process proceeds to step S142, and the register The number f0 of input pulse signals per second counted by the main counter 81 is stored in the register f. Next, it progresses to step S143 and subtraction of the fraction part in a measurement start point is performed. That is, as described above, using the values of N1 and n1 counted by the sub-counter 82 and stored in the register, f−n1 / N1 in the first half of the equation (4) is calculated and stored in the register f. Store. Then, it progresses to step S144 and the decimal part is added in the said measurement end point. That is, using the values of N2 and n2 counted by the sub-counter 82 and stored in the register, f + n2 / N2 in the latter half of the equation (4) is calculated and stored in the register f. That is, in steps S142, S143, and S144, the calculation of the above-described equation (4) is executed to calculate the frequency f of the input pulse signal for one second with high accuracy.
[0106]
Next, the process proceeds to step S145, and it is determined whether or not the value of the frequency f calculated in this way is equal to or higher than the flow frequency F1. When this result is NO, it is below the measurement lower limit frequency, so the process proceeds to step S148, and 0 is stored in the register Q for storing the instantaneous value. On the other hand, when the frequency f is equal to or higher than the flow frequency F1, the process proceeds to step S146, and an instantaneous flow rate value Q (= Ai × f + Bi) is calculated based on the equation (3). The correction coefficients Ai and Bi used here are the correction coefficients read from the EEPROM 17 in the step S63 (FIG. 15). Here, the instantaneous flow rate value Q is a value in units of “L / min”.
Subsequently, the process proceeds to step S147, and using the instantaneous flow rate value Q calculated in step S146, Q / 60 is added to the integrated flow rate value Qt to update the integrated flow rate value Qt. Here, Q is divided by 60 in order to convert the flow rate into 1 second. After the process of step S148 or step S147 is completed, both the calculation permission flags 1 and 2 are reset (step S149), and the flow rate calculation process is terminated.
[0107]
FIG. 24 is a flowchart for explaining the display processing in step S70 (FIG. 15). When this display process is started, first, in step S151, the set display mode is determined. Here, when the display mode is the instantaneous flow rate, the process proceeds to step S152, and the instantaneous flow rate value Q calculated in the flow rate calculation process is displayed on the display unit 31. This display mode is set in a key input process described later.
If the integrated flow rate display is selected, the process proceeds to step S153 to determine whether or not the fixed digit display is set. Here, when the fixed digit display (fixed decimal point type display) is set, the process proceeds to step S154, where the symbol “ud” indicating the upper digit display and the integrated flow rate are displayed on the display 31. Value of m ^Three Are displayed alternately for a predetermined period (for example, 5 seconds every 0.5 seconds). Subsequently, the process proceeds to step S155, where the symbol “Ld” indicating that the lower digit is displayed on the display 31 and the lower digit data in units of L of the integrated flow rate value are displayed in the same manner as in step S154. Display alternately for a predetermined period.
[0108]
On the other hand, when the display of the floating point system is set, the determination result of step S153 is NO, and the process proceeds to step S156. In step S156, the display unit 31 alternately displays a symbol “ud” indicating that the upper digit is displayed and data of three digits from the most significant digit of the integrated flow rate value for a predetermined period. When the unit display unit 32 is provided, the “m” is displayed together with the display. ^Three The unit display LED 35 is turned on. Then, the process proceeds to step S157 where the symbol “Ld” indicating that the lower digit is displayed on the display 31 and the fourth to sixth digits of data from the most significant digit of the integrated flow rate value are alternately displayed for a predetermined period. indicate. When the unit display section 32 is provided, the corresponding unit display LED 35 or 36 is turned on at the same time. That is, when the unit of the displayed fourth to sixth digit data is cubic meters, “m ^Three The unit display LED 35 is turned on. When the unit is liter, the “L” unit display LED 36 is turned on.
[0109]
FIG. 25 is a flowchart of the external output process S71 (FIG. 15). When the external output process is started, first, in step S161, it is determined whether or not the external output permission flag is set. This external output permission flag is a flag that is set at the timing of j = 3 in step S118 in the frequency measurement interrupt process (FIG. 20) (see FIG. 22). When the external output permission flag is not set, it is not the external output timing, and the external output process is terminated as it is.
As described above, in the present invention, since the timing of the external output is set to a predetermined timing, the deviation of data acquired by the external device is reduced, and high-accuracy monitoring is possible.
On the other hand, when the external output permission flag is set, the set signal system of the external output is determined in step S162. As described above, the selection of the output method is set by the jumper pin J2 in the function selection unit 12 (FIG. 11).
[0110]
Here, when the 4 to 20 mA transmission method is selected as the signal method, it is determined in step S163 whether or not the frequency f calculated in step S144 (FIG. 23) is equal to or higher than the flow frequency F1. If it is not equal to or higher than the flow frequency F1, the process proceeds to step S164, and all "0" are output to the 10-bit output latch. Further, when the frequency f is equal to or higher than the flow frequency F1, the process proceeds to step S165, and it is determined whether or not the instantaneous flow rate value Q calculated in step S144 (FIG. 23) is 110% or more of the rated flow rate value. . When the determination result is YES, the process proceeds to step S167 to output “1” to all the 10-bit latch outputs. On the other hand, if the decision result in the step S165 is NO, the process advances to a step S166 to output a 10-bit output corresponding to the calculated instantaneous flow rate value Q to the 10-bit latch. As a result, the 10-bit D / A converter 73 in the signal output unit 40 (FIG. 12) converts the 10-bit latch output into an analog signal, and the V / I converter 74 converts it into a corresponding current signal. A 4 to 20 mA transmission signal corresponding to the external device EXCT is output from the ~ 20 mA transmission signal output unit 75.
[0111]
On the other hand, when the jumper pin J2 in the function selection unit 12 is opened and the PWM signal method is selected as the output method, the process proceeds to step S168. Then, as in the case described above, it is determined whether or not the measured frequency f is equal to or higher than the flow frequency F1. If the result is NO, a pulse signal having a duty equivalent to 10 bits of “0” is output from the PWM output function unit built in the microcomputer 20 to the gate of the output transistor 76 (step S169). Further, when the measured frequency f is equal to or higher than the frequency with flow F1, the process proceeds to step S170, and it is determined whether or not the calculated instantaneous flow rate value Q is equal to or higher than 110% of the rating. If the determination result is NO, the process proceeds to step S171, and a pulse signal having a duty corresponding to the calculated instantaneous flow rate value Q (this is assumed to be 10-bit data) is output to the gate of the output transistor 76. Output to. When the instantaneous flow rate value Q is 110% or more of the rated value, the process proceeds to step S172, and a pulse signal having a duty equivalent to 10 bits of all 1 is output to the gate of the output transistor 76. Thus, a PWM signal having a 10-bit resolution corresponding to the instantaneous flow rate measured by the external device EXCT can be output via the output transistor 76.
[0112]
After outputting a signal based on the signal system set in step S167, S166 or S164 or step S172, S171 or S169 to the external device EXCT, the external output permission flag is reset in step S173. Ends the external output process.
As described above, in the present invention, since the measurement result having a resolution of 10 bits is used, it is possible to prevent propagation of errors and obtain a highly accurate measurement result.
[0113]
FIG. 26 is a flowchart for explaining the operation of the switch output process S72 (FIG. 15). When the switch output process is started, first, in step S181, it is determined whether or not the switch output flag is set. This switch output flag is a flag that is set in step S113 in the frequency measurement interrupt process (FIG. 20). When the high-speed switch output mode is set, every 0.2 seconds in step S113 (FIG. 20). This flag will be set. Here, in the normal switch output mode in which the switch output flag is not set, the process proceeds to step S185, and the measurement frequency f is written in the register f ′. On the other hand, in the high-speed output mode in which the switch output flag is set, the process proceeds to step S182, the count value f0 of the main counter 81 is read, and the count value f0 of the main counter read in the previous switch output process. A difference Δf from (old) is obtained, and 5 × Δf is written in the register f ′ (step S183). In step S184, the switch output flag is reset. The switch output flag is described as the SW output flag in the flowchart.
[0114]
That is, in the high-speed switch output mode in which the switch output flag is set, a value obtained by multiplying the difference Δf of the count value of the main counter 81 read in this switch output process executed every 0.2 seconds by 5 is obtained. As the frequency value f ′ for the switch output, in the normal switch output mode, the frequency value f calculated in step S144 (FIG. 23) (this value is calculated approximately every second) is used as the switch output. Is used as a frequency value f ′.
After determining the frequency value f ′ for the switch output in this way, the process proceeds to step S186, and the instantaneous flow rate value Q ′ (= Ai ×) corresponding to the frequency value f ′ based on the above-described equation (3). f ′ + Bi) is calculated.
[0115]
In step S187, the instantaneous flow rate value Q 'calculated in step S186 is compared with a preset lower limit flow rate value QL. As a result, when Q ′ ≦ QL, the process proceeds to step S188, where a high level is output to the gate of the output transistor 70, and an “L” level signal is output from the first output OUT1. At the same time, the first output LED 33 is turned on.
On the other hand, when Q ′> QL, the process proceeds to step S189 to determine whether or not the output OUT1 is at the “L” level. When the result is YES, the process further proceeds to step S190, where the instantaneous flow rate value Q ′ is QL + qL. more than It is determined whether or not. If the result of this determination is NO, the process proceeds to step S188.
Thus, in steps S189 and S190, the output OUT1 has a hysteresis characteristic. As a result, as shown in FIG. 26, the output OUT1 becomes “L” level when the instantaneous flow rate value Q ′ becomes less than the lower limit flow rate value QL, and becomes QL + qL or more when the instantaneous flow rate increases. It has a hysteresis characteristic so that it becomes “H” level when
On the other hand, when the determination result of step S189 is NO and when the determination result of step S190 is YES, the process proceeds to step S191, where a low level is output to the gate of the output transistor 70, and the first output OUT1 To output an “H” level signal. At the same time, the OUT1 LED 33 is turned off.
[0116]
After performing the process of step S188 or step S191 on the first output OUT1, the process proceeds to step S192, where the instantaneous flow rate value Q ′ is compared with the upper limit flow rate value QU. As a result, when QU ≦ Q ′, the process proceeds to step S193, a high level signal is output to the gate of the output transistor 71 (FIG. 12), and an “L” level is output to the second output OUT2. The second output LED 34 is turned on.
On the other hand, when Q ′ <QU, the process proceeds to step S194 to determine whether or not the second output OUT2 is at a low level. As a result, when it is at the low level, the process proceeds to step S195, and it is determined whether or not the instantaneous flow rate value Q ′ is equal to or less than QU−qU. Here, qU is a value that determines the hysteresis characteristic of the second switch output, and this second switch output OUT2 is changed from the high level to the low level when the instantaneous flow rate value Q ′ becomes equal to or higher than the upper limit flow rate value QU. When the instantaneous flow rate value Q ′ becomes QU−qU or less, the low level is inverted to the high level. Accordingly, when the determination result in step S195 is NO, the flow does not yet reverse the OUT2 output from the low level to the high level, and thus the process proceeds to step S193.
If the determination result in step S194 is NO or if the determination result in step S195 is YES, the process proceeds to step S196, and a low level signal is output to the gate of the output transistor 71 (FIG. 12). In addition, an “H” level is output to the second output OUT2, and the second output LED 34 is turned off.
[0117]
Thus, in the switch output processing of the present invention, the count value f0 of the main counter is checked every 0.2 seconds, and the difference Δf from the count value in the previous time (0.2 seconds before) is obtained. An approximate flow rate is calculated with Δf as a frequency for 1 second. Then, the approximate flow rate value calculated every 0.2 seconds is used for comparison with the upper limit / lower limit flow rate value. Therefore, it is possible to quickly detect the occurrence of an accident and send a signal as compared with the case where comparison is performed every measurement cycle (for example, 1 second) as in the past. In the case of an application example to be monitored, it is possible to prevent the equipment from being burned out.
[0118]
In the above description, the approximate frequency value is calculated based on the difference Δf in the count value of the main counter 81 every 0.2 seconds. However, other methods can be employed. That is, every 0.2 seconds, an approximate 1 is obtained by multiplying the count value f0 of the main counter 81 at that time by a different coefficient depending on which time of the first cycle the time is. This is a method of calculating an approximate flow rate by obtaining a frequency per second. Specifically, when the time is 0.2 seconds later, the count value f0 × 5 of the main counter is set to a frequency value for 1 second, and after 0.4 seconds, f0 × 2.5 is set to 0.6. Approximate flow rate is calculated by setting f0 × 1.667 for the second time and f0 × 1.25 for the frequency value for one second after 0.8 second, and the approximate flow rate and the upper / lower limit flow rate values. And compare. According to this method, it is possible to obtain an approximate flow rate with higher accuracy than in the case described above, but the control program becomes complicated because different coefficients are used.
[0119]
FIG. 27 is a process flowchart of the key input process S73 (FIG. 15). When this key input process is started, first, in step S201, any of the setting key (ENT key) 41, the up key (△ key) 42 or the down key (▽ key) 43 of the manual operation unit 13 is operated. It is determined whether or not it has been done. If no key operation is detected, the process proceeds to step S202, where the instantaneous flow rate value Q is displayed, and the key input process is terminated.
[0120]
When any operation of the operation keys 41 to 43 is detected, the process proceeds to step S203, and it is determined whether or not the operated key is the ENT key 41. When the operated key is the ENT key 41, the process proceeds to step S204, and the integrated flow rate value Qt display flag is set in a set state for a predetermined period (here, 10 seconds). Thereby, in step S151 of the display process (FIG. 24), the display mode is set to the integrated flow rate mode, and the integrated flow rate value Qt is displayed on the display unit 30. In step S205, it is determined whether the ENT key 41 has been operated again. If the ENT key 41 is not operated, the key input process is terminated as it is.
Thus, when the operator operates the ENT key 41 once, the integrated flow rate value Qt can be displayed on the display unit 30 for a predetermined period.
[0121]
On the other hand, when the ENT key 41 is operated again and the determination result in step S205 is YES, the process proceeds to step S206, and the L level point (lower limit flow rate value QL) of the output OUT1 is displayed on the display 31. The OUT1 LED 33 blinks. In this state, the operator can change the QL value using the △ key 42 or the ▽ key 43 and set it using the ENT key 41. When the ENT key 41 is operated and the setting of this QL is completed, the process proceeds to step S207, and similarly, the hysteresis value qL is displayed, and this qL is changed and set. Thereafter, the operation of the ENT key 41 causes the upper flow rate value QU to be displayed, changed and set in step S208, and the hysteresis value qU to be displayed, changed and set in step S209. The ENT key 41 is operated in step S209. Then, this key input process is terminated.
Thus, when the operator presses the ENT key 41 twice, the lower limit flow value QL, hysteresis value qL, upper limit flow value QU, and hysteresis value qU can be changed and set.
[0122]
On the other hand, when it is determined NO in step S203, that is, when the operated key is the △ key 42 or the ▽ key 43, the process proceeds to step S210, where the △ key 42 and the ▽ key 43 are pressed simultaneously. It is determined whether or not. When the determination result is YES, it is further determined whether or not the Δ key 42 and the ▽ key 43 are simultaneously pressed for a first predetermined time (for example, 5 seconds) (step S211). When the determination result of step S210 is NO, or when the determination result of step S211 is NO, that is, the Δ key 42 and the ▽ key 43 have not been pressed simultaneously for the first predetermined time (5 seconds) or more. At this time, the key input process is terminated as it is.
[0123]
On the other hand, if the △ key 42 and the ▽ key 43 are simultaneously pressed for the first predetermined time or longer and the determination result in step S211 is YES, the process proceeds to step S212, and the △ key 42 and the ▽ key 43 are simultaneously pressed. It is determined whether or not the second predetermined time (for example, 10 seconds) has been continued. When the determination result is YES, that is, when the Δ key 42 and the ▽ key 43 are continuously pressed for, for example, 10 seconds or more, the process proceeds to step S216, and the integrated flow rate value Qt stored in the RAM 85 and the EEPROM 17 is reached. Is cleared and the key input process is terminated.
As a result, the integrated flow value Qt can be cleared and integration from 0 can be started again.
[0124]
If the determination result in step S212 is NO, that is, if the △ key 42 and the ▽ key 43 are pressed simultaneously, for example, for 5 seconds or more and less than 10 seconds, the process proceeds to step S213, and the setting code is read out and handled accordingly. The aperture, material, and software version information are sequentially displayed for a predetermined period. This is the same as the display in step S64 (FIG. 15).
In step S214, the set display mode is displayed on the display 31. For example, when the display mode is set to fixed digit display, all three decimal points in the display 31 are lit, and when the display mode is set to floating digit display, the three decimal points in the display 31 are set. This is done by turning on and off one by one. At this time, the operator can change the display mode by operating the Δ key 42 or the ▽ key 43, and can set the display mode by operating the ENT key 41.
[0125]
When the operator operates the ENT key 41, the process proceeds to step S215, and the set switch output cycle is displayed on the display 31. This is performed, for example, by displaying “0.2” on the display 31 when the switch output cycle is set to a high speed and displaying “1.0” when the switch output period is set to a low speed. The operator can change the setting of the switch output cycle by operating the Δ key 42 or the ▽ key 43, and can set the switch output cycle by operating the ENT key 41. . Then, when the ENT key 41 is operated, this key input process is ended.
As described above, in this key input process, each of the parameters can be easily set and changed by using the △ key 42 and the ▽ key 43 mainly for changing the setting and using the ENT key 41 for confirmation. .
[0126]
In the above-described embodiment, the input pulse is counted and its period is measured by the rising edge of the input pulse. However, the time point of the falling edge of the input pulse may be used as a reference.
Further, the first period, the second period, and the period of the reference clock do not have to be the values used in the above-described embodiments, and may be optimal values according to individual cases. . For example, by making the reference clock faster, measurement with higher resolution can be performed.
Furthermore, in the above-described embodiment, the display 31 is an LED having a three-digit display unit. However, the display 31 is not limited to this, and may have any number of digits such as four digits or eight digits. it can. Furthermore, the display is not limited to the LED display, and other display elements such as an LCD can be used.
[0127]
【The invention's effect】
As described in detail above, the present invention Flowmeter Therefore, it is possible to perform highly accurate frequency measurement in a short time.
Moreover, when measuring continuously, the count value (n2, N2) used for the last measurement can be used also for the next measurement, and can be measured with high processing efficiency.
Flow rate of the present invention In total According to this, the instantaneous flow rate value can be measured with high accuracy for each first period.
In addition, the integrated flow rate can be displayed in multiple digits, and an easy-to-use flow meter can be provided.
Furthermore, based on the high-resolution measurement result, the measurement flow rate can be transmitted to the external device at a predetermined timing, and there is little data deviation and high-precision monitoring is possible.
Furthermore, the flow rate that allows the user to select whether or not to perform external switch output at high speed according to the application. Total Can be provided.
Furthermore, the flow rate that allows the setting value of the switch output to be easily changed Total Can be provided.
[Brief description of the drawings]
FIG. 1 of the present invention Flow meter Frequency measurement with frequency measurement method applied Part It is a figure which shows the example of a structure.
FIG. 2 of the present invention Flow meter It is a figure for demonstrating the frequency measurement method.
FIG. 3 shows frequency measurement shown in FIG. Part Is a flowchart of a main routine in FIG.
FIG. 4 shows frequency measurement shown in FIG. Part Is a flowchart of a first timer interrupt processing routine in FIG.
FIG. 5 shows frequency measurement shown in FIG. Part It is a flowchart of the count processing routine of the 2nd counter in.
FIG. 6 shows frequency measurement shown in FIG. Part It is a timing chart for demonstrating operation | movement.
[Fig. 7] of the present invention. Flow meter Frequency measurement method The Apply Shi It is a block diagram which shows an example of the basic composition of the flowmeter.
FIG. 8 is a diagram showing the structure of an embodiment of a flow meter of the present invention.
FIG. 9 is a diagram showing another embodiment of the display unit of the flowmeter of the present invention.
FIG. 10 is a diagram showing an example of the layout of printed circuit boards and the layout of components on the printed circuit board in the flowmeter of the present invention.
FIG. 11 is a block diagram showing a circuit configuration of a flow meter of the present invention.
FIG. 12 is a block diagram showing a configuration of a power supply unit and a signal output unit of the flowmeter of the present invention.
FIG. 13 is a diagram showing an example of a memory map of ROM, RAM, and EEPROM in the flowmeter of the present invention.
FIG. 14 is a flowchart of a main routine of the flow meter of the present invention.
FIG. 15 is a flowchart of an instantaneous flow meter processing program of the flow meter of the present invention.
FIG. 16 is a diagram for explaining a display form in step S64 in FIG.
FIG. 17 is a flowchart of a power supply voltage check interrupt process of the flowmeter of the present invention.
FIG. 18 is a diagram showing a connection state during the adjustment inspection process of the flowmeter of the present invention.
FIG. 19 is a flowchart of a flow meter adjustment inspection process according to the present invention.
FIG. 20 is a flowchart of frequency measurement interrupt processing of the flowmeter of the present invention.
FIG. 21 is a flowchart of a 1 msec clock counting process of the flow meter of the present invention.
FIG. 22 is a diagram for explaining the frequency measurement interrupt process and the 1 msec clock counting process;
FIG. 23 is a flowchart of flow rate calculation processing of the flowmeter of the present invention.
FIG. 24 is a flowchart of the display process of the flowmeter of the present invention.
FIG. 25 is a flowchart of external output processing of the flowmeter of the present invention.
FIG. 26 is a flowchart of switch output processing of the flowmeter of the present invention.
FIG. 27 is a flowchart of key input processing of the flowmeter of the present invention.
[Explanation of symbols]
1 Frequency detector
2 First counter
3 Second counter
4 First timer
5 Reference clock generator
6 arithmetic processing part
7 Control unit
8 Display section
9 Output section
11 Sensor part
12 Function selection section
13 Manual operation part (key input part)
14 Reset signal output unit (power-on reset circuit)
15 Watchdog timer section
16 Voltage drop detector
17 Nonvolatile memory (EEPROM)
20 Control unit (microcomputer)
30 Display section
31 Display (data display unit)
33 Output 1 display unit (OUT1LED)
34 Output 2 display unit (OUT2LED)
35, 36 Unit display LED
40 Signal output section
41 Setting key (ENT key)
42 Up key (△ key)
43 Down key (▽ key)
45 Power supply
50 Weighing unit body
61-63 Printed circuit board
70, 71, 76, 77 Output transistor
73 Digital-analog converter (D / A converter)
74 Voltage-current converter (V / I converter)
75 4-20mA transmission signal output section
78 DC stabilized power supply circuit
81 First counter (main counter)
82 Second counter (sub-counter)
83 Timer registers
84 ROM
85 RAM

Claims (3)

A sensor unit that outputs a pulse signal having a frequency corresponding to the flow rate to be measured;
A first signal generator for generating a first signal having a first period;
A first measurement unit that counts the number of pulses output from the sensor unit during the period of the first cycle in response to the first signal;
A second measuring unit for measuring a position of the first signal in a pulse including the first signal in its cycle;
A first calculation unit that calculates a frequency of the pulse signal for each first period based on a count value by the first measurement unit and a measurement result by the second measurement unit;
A flow meter having a second calculation unit for calculating an instantaneous flow rate based on the calculated frequency of the pulse signal,
Synchronized with the first signal and a second signal generator for generating a second signal having a second period divided by the constant lower limit frequency measuring said first period,
When the state in which the pulse period in the pulse signal is equal to the period corresponding to the commercial AC power frequency continues for a predetermined number of times, the measurement result is invalidated, and
Flowmeter, characterized in that the timing of the computation operation of each operation unit based on an output of said second signal generator is controlled. A sensor unit that outputs a pulse signal having a frequency corresponding to the flow rate to be measured;
A first signal generator for generating a first signal having a first period;
A first measurement unit that counts the number of pulses output from the sensor unit during the period of the first cycle in response to the first signal;
A second measuring unit for measuring a position of the first signal in a pulse including the first signal in its cycle;
A first calculation unit that calculates a frequency of the pulse signal for each first period based on a count value by the first measurement unit and a measurement result by the second measurement unit;
A flow meter having a second calculation unit for calculating an instantaneous flow rate based on the calculated frequency of the pulse signal,
A comparison unit that compares a preset flow rate value set in advance with the instantaneous flow rate value calculated by the second calculation unit;
A switch output unit that outputs the comparison result as a digital signal;
The comparison unit includes a normal mode for comparing the instantaneous flow rate value calculated based on the output of the first calculation unit for each of the first period and said set flow rate value, measure the first cycle It has two operation modes of a high speed mode for comparing the instantaneous flow rate value calculated based on the measurement value of the first measurement unit and the set flow rate value every second period divided by the lower limit frequency. A flow meter. A plurality of values can be set as the set flow rate value, and the switch output unit is controlled by a logical sum of comparison results for the plurality of set flow rate values. Item 3. The flow meter according to Item 2 .

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