JP3216768B2 - Karman vortex flowmeter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flow rate calculation output control means in a Karman vortex flow meter for measuring a flow rate of air, water, or the like.

[0002]

2. Description of the Related Art In a Karman vortex flowmeter, when a columnar obstacle is placed in a fluid flow, vortices are alternately generated from both ends of the obstacle perpendicular to the flow direction at a frequency proportional to the flow velocity of the fluid. This is a flow meter that utilizes the phenomenon that occurs. The Karman vortex flowmeter has a flow detector that amplifies the Karman vortex sensor, which consists of a piezoelectric element that captures slight pressure fluctuations in the fluid when vortices are generated by obstacles, and the weak signal output by the Karman vortex sensor. And a waveform shaping circuit for outputting a pulse signal having a constant waveform when the value exceeds a predetermined value. A Kalman pulse signal having a frequency corresponding to the flow rate of the fluid is transmitted from the flow rate detection unit.

[0003] In a transmission section for detecting the above-mentioned Kalman pulse signal and calculating and outputting the flow rate, conventionally, the transmission section between the Karman vortex flow rate detection section and the Kalman pulse signal input to the transmission section within a predetermined fixed sampling period is conventionally used. Measure the sum of the cycles and the total number of pulse signals, divide the total number of pulse signals by the sum of the cycles between pulse signals to determine the frequency of the Kalman pulse signal in the sampling cycle, and convert this frequency value to a flow rate value By doing so, the flow rate of the fluid is measured and output.

[0004]

The flow rate detector of the Karman vortex flow meter amplifies a weak signal output from the Karman vortex sensor, and outputs a shaped pulse signal having a constant waveform when this value exceeds a certain value. The fluctuation of the fluid flow
The output signal value of the Kalman vortex sensor decreases due to factors such as "pulse missing" where the shaped pulse signal is not transmitted
May occur.

When this "pulse missing" occurs, the transmission unit according to the prior art counts the total number of input pulse signals less by the amount of the "pulse missing", so that the frequency obtained by the calculation is lower than the actual frequency of the Kalman pulse. The frequency becomes low and a large error occurs in the flow measurement output value. Therefore, each time the period between the Kalman pulse signals input from the vortex flow detecting unit is detected and measured, the transmission unit is provided with an area for storing and storing the output values in the order of output in the RAM, and the reference period timer sets the sampling period. When the frequency is calculated, the flow rate is calculated and the flow rate is calculated.
A reference cycle in a sampling period is determined based on the value of the measurement cycle stored in the measurement cycle counter area set in the RAM, and the value of the reference cycle is sequentially compared with each cycle measurement value stored in the measurement cycle counter area. Then, when a cycle measurement value having a deviation equal to or more than a predetermined fixed ratio is detected from the reference value, a process of excluding the cycle measurement value and the count of pulses giving the cycle measurement value from the integration target data in the sampling period is performed. Even if "pulse missing" occurs in which the shaped pulse signal is not transmitted and the value of the period longer than the normal pulse period is stored in the measurement period counter area, this value is used to calculate the frequency and flow rate. It is possible to get the correct frequency and flow rate values to be excluded from the data used for It requires large-capacity storage area as a storage means for storing, not realistic.

According to the present invention, when "pulse omission" occurs, the measured value is invalidated if the pulse is corrected or if the correction is not appropriate, and a small-capacity storage that does not output an erroneous flow rate measurement result is provided. An object of the present invention is to provide a transmission section of a Karman vortex flowmeter composed of regions and improve the reliability of flow measurement by the Karman vortex flowmeter.

[0007]

When a "pulse missing" of one pulse occurs in the Karman vortex flowmeter, the pulse count value during the sampling cycle is counted down by one count, and when the "pulse missing" occurs, the adjacent pulse count is reduced. The period between pulses is measured as about twice as long as there is no "pulse missing". However, in a normal fluid flow, even if there is a very extreme sudden change in the flow rate, the measurement result of adjacent periods is 2 times.
There is nothing different than double.

Therefore, in order to prevent the occurrence of an error due to "missing pulse" in the Karman vortex flowmeter, in the present invention, the transmission section of the Karman vortex flowmeter performs a calculation and an output step process at a timing given by a system clock. A microcomputer, a reference period timer for providing a sampling period for executing a calculation output process, a pulse period measurement counter for measuring a time interval between pulse signals transmitted by the Karman vortex flow detector, and a measurement output of the pulse period measurement counter. A leading period buffer area for storing three or more values in order of output and an area for temporarily storing count values and mantissa values generated in the course of arithmetic processing executed in the microcomputer are set. RAM and
A cycle measurement program, which is composed of a ROM in which the procedure of the arithmetic processing is stored and an output unit for outputting the result of the arithmetic processing, is called by the microcomputer from the ROM and executed when the reference cycle timer counts up the sampling cycle. The number of measurement cycle values stored in the head cycle buffer area set in the RAM is checked, and when the number of stored data reaches a predetermined number, the cycle reference in the sampling period is determined based on the storage value of the measurement cycle. Each time the Karman vortex flow rate detection unit transmits a Karman vortex signal, a value obtained by multiplying the period reference value measured by the pulse period measurement counter by a predetermined constant of more than 1 and less than 2 is obtained. The cycle measurement value exceeds the first reference value and the second reference value obtained by multiplying the cycle reference value by a predetermined constant of more than 2 and less than 3 as compared with the first reference value. When the value does not exceed the reference value, a process of adding 1 to the number of pulse signals transmitted by the Karman vortex flow rate detection unit is performed. When the value exceeds the second reference value, the period measurement value and the transmission of the Karman vortex signal at this time are performed. When the reference period timer counts up the sampling period, the microcomputer calculates the flow rate calculation program called by the microcomputer from the ROM and adds the Kalman vortex signal with the integrated value of the period measurement value obtained above. A process is provided for obtaining the flow rate value during the sampling period by dividing the integrated value of the number of transmissions.

[0009]

In the transmission section of the Karman vortex flow meter according to the present invention, at the beginning of each sampling cycle, a period measurement value between the output pulse signals of the Karman vortex flow detection section is measured in a predetermined number of leading cycle buffers. When the storage of the cycle measurement value in the first cycle buffer is completed, the cycle reference value for this sampling period is determined based on the storage value of the measurement cycle in the course of the processing of the cycle measurement program. Each time the detection unit transmits the Karman vortex signal, the period reference value is compared with the value of the period measured by the pulse period measurement counter, and the period measurement value is obtained by multiplying the period reference value by a predetermined constant. If the reference value does not exceed 1, the cycle measurement value and the number of transmitted Karman vortex signals are integrated, and if the cycle measurement value exceeds the first reference value, the cycle reference value is preset to the cycle reference value. Only when the second measured value does not exceed the second reference value obtained by multiplying by the constant, the period measurement value is integrated for two periods. Therefore, when the reference period timer counts up the sampling period, the period measurement value and the pulse signal are counted. The integrated value of the number of transmissions has been corrected for the error due to the occurrence of “pulse missing”.

[0010]

FIG. 1 shows a schematic configuration of an embodiment of the Karman vortex flowmeter according to the present invention. In FIG. 1, reference numeral 1 denotes a Karman vortex flow rate detection unit including a Karman vortex sensor that generates a signal at a period inversely proportional to the flow velocity of a fluid, and a waveform shaping circuit that amplifies and shapes the signal of the Karman vortex sensor and outputs the signal. Reference numeral 2 denotes a transmission unit including the following 3 to 9 components for counting the Karman vortex pulse signal transmitted by the flow rate detection unit 1 at each predetermined sampling period, calculating the flow value, and outputting the calculated value. .

In the transmission unit 2, a microcomputer 3 receives the output pulse signal of the Karman vortex flow rate detection unit 1, performs a calculation for obtaining the flow rate, and performs a process of outputting the calculation. Step operation is performed at the timing. Reference numeral 5 denotes a reference cycle timer (SCT) that determines the execution cycle of the measurement operation processing performed by receiving the output pulse signal of the Karman vortex flow rate detector 1, and 6 is triggered by a pulse signal transmitted by the flow rate detector 1. It is started and measures the time interval until the next pulse signal is input. When the next pulse signal is input and the measured value up to this time is transferred to the microcomputer 3, the measured value is cleared to zero, Is a pulse cycle measurement counter in which the measurement of the time interval until the arrival of the pulse is restarted. The output signal of the flow rate detection unit 1 is supplied to the microcomputer 3 via an interrupt input terminal INT2 relating to the pulse frequency measurement. Is input to

The ROM 8 is a read-only storage unit in which the operation process of the microcomputer 3 is stored. The storage program includes a reference period timer 5 which counts up a sampling period and outputs an interrupt request signal INT.
1 is input to the microcomputer 3, the flow rate calculation program (82) to be called and processed, and when the flow rate detection unit 1 transmits a pulse, the pulse is transmitted to the interrupt signal INT.
2 and a period measurement program (81) that is started.

The RAM 7 is a storage means which can be written and read at any time for temporarily storing a code (flag) indicating a state requiring temporary storage and a count value in the course of execution of the arithmetic processing of the microcomputer 3. In the storage area of the RAM 7, a pulse number counter (NP) for counting the pulses output by the Karman vortex flow rate detection unit 1 in each sampling period, and a period measurement between successive pulses measured and output by the pulse period measurement counter 6 A leading cycle buffer (TB (1) to TB (n)) for storing and storing a plurality of predetermined values n in the order of output, and a pulse cycle measuring counter 6 after the cycle measuring value stored in the leading cycle buffer. A measurement cycle counter (TF (r)) for temporarily storing the cycle measurement value transmitted by the first cycle until the next cycle measurement value is output, and an integration cycle counter (TT) for integrating and storing the value of the measurement cycle.
C) is secured, and the pulse number counter (NP) and the integration period counter (TTC) are provided with respective counters for temporarily holding the values stored in the respective counters during execution of the calculation output processing. The corresponding buffer areas (NB) and (T
TB) and the number of data to be stored in the first cycle buffer (S
A storage area for setting values used in the process of P), the provisional reference period value (TRI), other calculation processes, and variables in the middle of calculation is secured.

In addition, the RAM 7 has a measurement end flag (indicating the end of the integration) for terminating the integration of the pulse interval measurement result when the integrated value TTC of the pulse period integration counter exceeds a predetermined upper limit MTC. An area for storing an EDF) and a pulse interval measurement flag (PTF) indicating whether the pulse interval measurement integration process is being executed or is in a standby state are also secured. Sampling time counter (STC) that stores the count value to be counted in determining the flow rate measurement cycle
Is provided. The sampling period value STC set in the sampling time counter (STC)
In order to maintain the measurement accuracy of the flow rate, a time sufficiently longer than the cycle of the output pulse transmitted by the vortex flow rate detection unit is set within a range that can follow the time variation of the flow rate.

Next, FIG. 2 to FIG. 5 show the flow of one embodiment of an arithmetic processing program executed by the microcomputer 3 based on the first invention of the present application. Will be described. Transmission section 2 of the Karman vortex flow meter according to the invention illustrated in FIG.
When the standby is set after the initial condition is set, the interrupt from the reference period timer 5
Enters an interrupt standby state in which an interrupt caused by an output pulse of the flow rate detection unit 1 that occurs at a time interval shorter than a sampling period determined by a set value of a sampling time counter (STC) counted by the lower order is lower.

First, an interrupting process by an output pulse of the Karman vortex flow rate detecting unit 1 which frequently interrupts will be described. When the output pulse of the Karman vortex flow detection unit 1 is input to the interrupt request terminal 1NT2 of the microcomputer 3,
The period measurement program (81) in the flow of FIG. 2 is called from the ROM 8 and the processing is performed (P0).

The period measurement program (81) checks the state of the period measurement flag PTF by temporarily masking the interruption by the output pulse when there is an interruption by the output pulse of the Kalman vortex flow detector 1 (P1, P1). P2) When the PTF is 0 indicating that the pulse interval is not being measured, to measure the period from this input pulse to the next input pulse,
The count value PCC of the pulse period measurement counter 6 is initialized and started (P3), the pulse number counter NP and the pulse period integration counter TTC are also initialized (P4), and the period measurement flag PTF is set to 1 indicating that the measurement is in progress. Set (P
5) Permit interruption by the output pulse of the Karman vortex flow detector 1 (P6), and return from the interruption.

On the other hand, when the period measurement flag PTF indicates 1 during measurement, the stored value N of the pulse number counter is set.
P is incremented (P7), and it is checked whether or not this value has reached a predetermined value SP of 3 or more as the number of period measurement data for obtaining the reference period (P8). The measured value PCC is stored in the NP-th period measurement buffer TB (NP), the period measurement counter 6 is initialized (P9), and the transferred value TB of the measurement period counter is transferred.
After adding (NP) to the stored value TTC of the pulse period integration counter (P10), a calculation process for obtaining a reference period is performed based on a predetermined program (P11), and the stored value NP of the pulse number counter exceeds SP. The measurement value PCC of the pulse period measurement counter 6 is
After the value TF (r) of the measurement cycle counter transferred and added to the stored value TTC of the pulse cycle integration counter (P13), the pulse missing discrimination correction processing based on a predetermined program is performed. Is performed (P14).

When the above-described reference cycle calculation or pulse omission determination correction processing is completed, the stored value TTC of the pulse cycle integration counter becomes the upper limit set value M of the predetermined pulse interval integration value.
Compared with TC (P15), if TTC does not exceed MTC, the interrupt by the output pulse of the Karman vortex flow rate detection unit 1 previously masked is permitted (P6) and the process returns from the interrupt (P17). Measurement end flag E
DF is set to 1 indicating the end of measurement (P16), and the process returns from the interrupt without permitting the interrupt (P17). continue,
When the cycle reference value calculation processing program called in the cycle measurement program started by the interruption by the output pulse of the Karman vortex flow rate detection unit 1 is realized when the number SP of data used to determine the cycle reference value is three. This will be described with reference to FIG.

The reference period calculation processing program of the embodiment shown in FIG. 3 is called when the count number NP of the pulse number counter is equal to or less than 3 defined as the value of the initial sampling data number SP in step P11 of the period measurement program. First, the count number NP of the pulse number counter is SP value 3
Is determined (R1), and if it is not 3, the program immediately returns to the calling cycle measurement program (R1).
If 0) is equal to 3, the period measurement values stored in the period measurement buffers TB (1), TB (2), and TB (3) as the first three data of the pulse period measurement result are compared with each other. Then, an average value TR of the remaining two data excluding the maximum value data TM is obtained and determined as a cycle reference value TR (R2
R7).

When one pulse is missed, the pulse period is measured to be approximately doubled. Therefore, a value C × TR obtained by multiplying the cycle reference value TR obtained as described above by a constant coefficient C less than 2 and the first three data TB (1), T
B (2) and TB (3) are compared with the maximum value TM, and C ×
If the value exceeds TR, occurrence of "pulse missing" is recognized. Therefore, the integrated cycle counter held value TTC to which the incorrect measurement cycle value is added is replaced with 3 × TR as an approximate value of the correct value. (R9) to return to the calling cycle measurement program. Note that the value of the constant C less than 2 in the above processing is set to, for example, 1.5 or the like in order to stably and reliably detect missing one pulse.

Next, after the count number NP of the pulse number counter exceeds the value of the number SP of data used to determine the cycle reference value in the cycle measurement program and the value of the reference cycle is determined, the Karman vortex is determined. FIG. 4 shows a flow of one embodiment of the pulse missing discrimination correction processing program called in the processing when the output pulse of the flow rate detector 1 is input, and this will be described.

As described above, when one pulse of "pulse missing" occurs in the Karman vortex flowmeter, the pulse count value during the sampling period is counted down by one count, and when the "pulse missing" occurs, the adjacent pulse count is reduced. The period between pulses is measured as about twice as long as there is no "pulse missing". However, in a normal fluid flow, even if there is a very extreme sudden change in the flow rate, the measurement result of adjacent periods is 2 times. Nothing is different.

Therefore, when the pulse missing discrimination correction program is called, first, the cycle value TF measured by the current output pulse of the Karman vortex flow rate detection unit 1 is called.
(r) is replaced by a coefficient of a value less than 2 to the value TR of the reference period, for example,
The value multiplied by 1.5 is compared with 1.5 × TR (E1). If the measurement period TF (r) does not exceed this value, it is immediately returned to the caller assuming that "pulse missing" is not recognized (E5). If it exceeds, the value of the measurement period TF is checked in order to confirm whether the occurrence of “pulse missing” is a single pulse or two or more “pulse missing”.
(r) is a coefficient of a value of 2 or more and less than 3 to the value TR of the reference cycle,
For example, a value multiplied by 2.5 is compared with 2.5 × TR (E2). If the measurement cycle TF (r) does not exceed this value, it is recognized that “pulse missing” occurs only once, so The number of missing pulses 1 is added to the value NP (E4), and the process returns to the calling source (E5).

On the other hand, if the value TF (r) of the measurement cycle exceeds 2.5 times the value TR of the reference cycle, two or more pulses may be missing, and the reliability of the cycle measurement is ensured. In order to make the current measurement result invalid, the value TF (r) of the current measurement cycle is subtracted from the accumulated cycle counter holding value TTC and one count is subtracted from the count number NP of the pulse number counter (E3 ) Return to the caller (E5).

According to the above-described period measurement program, when a plurality of period measurement data obtained at the beginning of the sampling period is used and a period reference value excluding "pulse omission" is set, the Karman vortex flow rate is detected. When there is an interruption due to the output pulse of the unit 1, the occurrence of "pulse missing" is detected based on this cycle reference value. If it is recognized that "pulse missing" occurs only once, the value of the pulse number counter is used. The missing pulse is corrected by adding 1 to NP, and when the occurrence of “missing pulse” of two or more pulses is detected, the value TF ( r) is subtracted, and one count is subtracted from the count number NP of the pulse number counter to invalidate this measurement result. As the stored value NP of the loose number counter and the stored value TTC of the integration period counter, uncertain data is excluded and "pulse missing" corrected data is obtained.

When the reference cycle timer 5 counts up the sampling cycle counter STC and an interrupt occurs to terminate the sampling cycle, the stored value NP of the pulse number counter and the stored value TTC of the integration cycle counter are used in this sampling cycle. The flow of one embodiment of the flow rate calculation program (82) for obtaining the value of the flow rate will be described with reference to FIG.

As shown in FIG. 5, when the flow rate calculation program (82) is started by an interrupt from the reference period timer 5, the interrupt by the output pulse of the Karman vortex flow rate detector 1 is first masked once. Then, the state of the measurement end flag (EDF) is checked (S1, S2). When the measurement end flag (EDF) is 1 and the end of the pulse cycle measurement is indicated, the measurement values stored in the pulse number counter (NP) and the integration cycle counter (TTC) are used during the execution of the flow value calculation processing. Buffers (NB, TT) provided corresponding to the respective counters for holding
The transfer is retracted to B) (S3). On the other hand, if the measurement end flag (EDF) is 0, indicating that the measurement has not been completed, the pulse number buffer (NB) and the integration period buffer (TTB) are cleared to zero to end the measurement of the pulse period. The standby state is maintained (S4).

When the processing based on the above-mentioned measurement end flag (EDF) inspection result is completed, the measurement end flag (EDF)
And the pulse period measurement flag (PTF) is set to 0 to indicate that the period measurement of the output pulse signal of the Karman vortex flow detector 1 has not been started and has not been completed (S5). Then, the interruption from the flow rate detection unit 1 masked in step S1 is permitted (S6). Therefore, when this process is completed, the transmission unit 2 has returned to the interrupt standby state due to the output pulse of the flow rate detection unit 1.

Subsequently, the stored value of the pulse number buffer NB is checked (S7). If this value is 0, a process of directly setting the flow rate value Q to 0 is performed (S9), and if the stored value of NB is not 0, The value of the frequency buffer is calculated by dividing the value NB of the pulse number buffer by the value TTB of the integration period buffer, and multiplying this value by the conversion coefficient K to obtain the flow rate value Q (S8). After executing the output process of the flow value Q (S10), the process returns from the interrupt (S11).

By the way, if the pulse height discrimination set value of the waveform shaping circuit of the Karman vortex flow rate detecting section 1 is properly adjusted, even if a pulse is missing, it occurs accidentally and independently. Therefore, the value obtained by averaging three or more of the period measurement results of the output pulse signal of the Karman vortex flow rate detector 1 measured by the period measurement program is twice the period value when no pulse omission occurs. Events that exceed are not usually encountered. FIG. 6 shows a flow of an embodiment of the reference cycle calculation program based on the second invention for determining the value of the reference cycle using this fact, and this embodiment will be described. For the sake of simplicity, the number SP of data used to determine the cycle reference value is 3 in this embodiment as well.

When the reference period calculation processing program of the embodiment of FIG. 6 is called, first, it is determined whether or not the count number NP of the pulse number counter has reached the value 3 of SP (K
1) If it is not 3, the program immediately returns to the calling cycle measurement program (K10). If it is equal to 3, the cycle measurement buffers TB (1), TB (2), and TB (1), as the first three data of the pulse cycle measurement result. And the average value of the cycle measurement values stored in TB (3) is calculated, and this is calculated as the value TR of the provisional reference cycle.
I (K2). Then, a value C × TRI obtained by multiplying the provisional reference cycle value TRI by a constant coefficient C less than 2 and a cycle measurement value TB (i) (i = 1, 2, 3) stored in the cycle measurement buffer are sequentially compared. However, if the value of TB (i) exceeds the above-mentioned discrimination value and "pulse missing" is recognized, the cycle measurement value TB (i) when this "pulse missing" occurs from the integrated value TTC stored in the integrating cycle counter. ) Is subtracted and the provisional reference cycle value TRI that is close to the true value is added to obtain a new integrated cycle value TTC (K3 to 8).

When the "pulse missing" detection correction process based on the cycle measurement value comparison is completed, the correction integration cycle value T
The value obtained by dividing TC by the value 3 of the number of detected pulses is set as the reference period value TR (K9), and the process returns to the caller's period measurement program (K10). Further, even if a pulse dropout occurs during the measurement of the cycle that determines the reference cycle of the Karman vortex signal pulse, if the pulse dropout is within one cycle, the value of the measurement cycle is made valid. FIG. 7 shows a flow of an embodiment of the arithmetic program, and this embodiment will be described. For the sake of simplicity, the number SP of data used for determining the cycle reference value TR is set to 3 in this embodiment.

In the reference cycle calculation processing program of the embodiment shown in FIG. 7, every time a Karman vortex signal pulse is inputted from the Karman vortex flow rate detecting section 1, the value of the measurement cycle TB (i) (i) measured by the signal pulse is input. = 1, 2, 3) is the value T of the measurement period measured by the previous Karman vortex signal pulse input.
The replacement process is performed so that the measured values are arranged in order of magnitude, for example, in ascending order, as compared with B (i) (T1 to T8).

After each replacement process, the cycle measurement values TB (2) and TB (3) other than the minimum cycle measurement value TB (1)
In order to determine whether or not “pulse missing” of one cycle or more has occurred in the measurement of (1), first, the minimum cycle measurement value TB (1)
Multiplied by a constant less than 2, for example 1.5, the first upper limit 1.5T
B (1) is compared with a measured value other than TB (1). If the measured value exceeds the first upper limit, “missing pulse” is recognized. In order to determine whether the period exceeds the period, first, the minimum period measurement value TB
Second upper limit value obtained by multiplying (1) by a constant less than 3, for example, 2.5
2.5 Compare TB (1) with measured values other than TB (1). If the measured value exceeds the second upper limit, "pulse missing" is recognized as one or more cycles, so reliability is ensured. Therefore, the measurement result is not added to the measurement data for determining the reference cycle, and the cycle measurement value is subtracted from the integration cycle counter value TTC, and 1 is subtracted from the pulse number counter value NP (T9 to T11). And T13 to T15).

On the other hand, if the measured period other than TB (1) exceeds the first upper limit 1.5TB (1) but does not exceed the second upper limit, it is determined that "pulse missing" has occurred for one period. Is done. When "pulse missing" is 1, the pulse period measurement counter PCC measures a period equivalent to about two periods, and this value is added to the integration period counter TTC, but the pulse number counter NP counts one missing pulse. Minutes have not been added.
Therefore, when the cycle measurement value exceeds the first upper limit value but does not exceed the second upper limit value, the pulse number counter NP is corrected by adding 1 (T12 and T16).

When the above processing is repeated until the integrated value of the pulse number counter NP becomes a predetermined number of times SP or more, and in this embodiment, becomes 3 or more, the integrated value of the actual cycle measurement value is stored in the integrating cycle counter TTC. In addition, since the pulse number counter NP stores the correct pulse number corrected for missing pulses, the reference period TR is obtained by dividing the stored value TTC of the integration period counter by the count value NP of the pulse number counter. Thereafter, the process returns from the reference cycle calculation (T18, T19).

[0038]

In the transmission section of the Karman vortex flowmeter according to the present invention, the measurement period counter area for storing the measurement value of the pulse period measurement counter cannot store all the measurement values, but only a plurality of data. Is set in a narrow area that can be stored, and when a predetermined number of pulse period measurement values are obtained, a reference period in the sampling period is determined based on the obtained pulse period measurement values, and thereafter, the Karman vortex flow rate detection unit Each time the pulse period of the output pulse is measured by the pulse period measurement counter, this measured value is compared with the value of the reference period, and if the missing pulse can be corrected with reliability, generation of the period measurement value and one Kalman vortex signal Is accumulated in the integration period counter and the pulse number counter, so that when the sampling period ends, the measured value excluding the effect of "pulse missing" is The Kalman vortex flowmeter outputs the correct flow rate value even if "pulse missing" occurs using a small-scale RAM, since the flow rate can be directly calculated based on this value remaining in the counter and the pulse number counter. The effect of being able to obtain is obtained.

When a predetermined number of cycle measurement results, for example, three data, are obtained, the average value is obtained as a provisional reference cycle, and the provisional reference cycle value and each cycle measurement value are sequentially compared to obtain a pulse. The process of subtracting the cycle measurement value TB (i) at the time of the omission from the value of the integration cycle and adding a temporary reference cycle value TRI that is close to the true value instead to obtain a new integration cycle value is a simple process. The processing speed is fast because
This method is effectively applied to an object in which the flow rate is largely fluctuated with time and the sampling cycle should be set short.

On the other hand, in the measurement for determining the reference period, every time the pulse period of the output pulse of the Karman vortex flow rate detection unit is measured by the pulse period measurement counter, (the measurement period measured by the previous Karman vortex signal pulse input) Performs permutation processing so that the measured values are arranged in the order of magnitude (compared with the values), and checks for missing pulses by comparing the magnitude of each measured value, and corrects for missing pulses while maintaining reliability. According to the transmission unit provided with the reference cycle calculation program in which the cycle measurement value and the generation of one Kalman vortex signal are integrated in the integration cycle counter and the pulse number counter in a case where the pulse missing occurs, Since the measurement results are utilized within the range where the degree can be maintained, accurate reference cycle values can be reliably obtained in a short period of time, and the streamline distribution is unstable and causes pulse omission Effect that noise can be effectively applied to a prone measured occurs.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of an embodiment of a Karman vortex flowmeter according to the present invention.

FIG. 2 is a flowchart of a cycle measurement program started by an output pulse interrupt of a flow detection unit.

FIG. 3 is a program flow chart of a process for obtaining a reference cycle.

FIG. 4 is a flowchart of a pulse missing discrimination correction program.

FIG. 5 is a flowchart of a flow rate calculation program started by a reference period timer interrupt.

FIG. 6 is a program flow diagram of another embodiment for obtaining a reference cycle.

FIG. 7 is a program flow diagram of another embodiment for obtaining a reference cycle.

[Explanation of symbols]

 Reference Signs List 1 Karman vortex flow detector 2 Transmitter 3 Microcomputer 4 System clock 5 Reference period timer 6 Pulse period measurement counter 7 RAM PTF period measurement flag EDF measurement end flag NP Pulse number counter NB Pulse number buffer TB (i) Start period buffer (i = 1,2, n) TF (r) Measurement period counter TB (r) Measurement period buffer TTC Integration period counter TTB Integration period buffer STC Sampling period counter 8 ROM 81 Period measurement program 82 Flow rate calculation program 9 Output signal converter

Continuation of the front page (56) References JP-A-60-56220 (JP, A) JP-A-61-96414 (JP, A) JP-A-2-266230 (JP, A) JP-A-63-63722 (JP) JP-U 6-30725 (JP, U) Patent 3147648 (JP, B2) Patent 2646527 (JP, B2) JP-B 63-2449 (JP, B2) JP-B 4-32972 (JP, B2) Japanese Patent Publication No. 4-32973 (JP, B2) Japanese Patent Publication No. 5-70086 (JP, B2) Japanese Patent Publication No. 6-95028 (JP, B2) (58) Fields surveyed (Int. Cl. ⁷ , DB name) G01F 1/32

Claims (3)

(57) [Claims] 1. A Karman vortex flow rate detector comprising a Karman vortex sensor having a flow rate detection end as a flow rate detector, and a transmission section for performing a calculation and an output process for calculating a flow rate by measuring an output pulse signal of the flow rate detector. The transmission unit is a microcomputer that performs a step process of calculation and output at a timing given by a system clock, a reference period timer that provides a sampling period for executing a calculation output process, and the Karman vortex flow rate detection unit. A pulse cycle measurement counter for measuring a time interval between pulse signals to be transmitted, a head cycle buffer area for storing at least three or more of the measured output values of the pulse cycle measurement counter in the order of output, and the microcomputer is executed by the microcomputer. A RAM in which an area for temporarily storing a count value and a mantissa value generated in the course of the arithmetic processing is set; A ROM in which the procedure of the arithmetic processing is stored; and an output unit for outputting the result of the arithmetic processing. When the Karman vortex flow rate detection unit transmits a Karman vortex signal, the microcomputer calls and executes the program from the ROM. The cycle measurement program checks the number of measurement cycle values stored in the head cycle buffer area set in the RAM, and when the number of stored data reaches a predetermined number, performs sampling based on the stored value of the measurement cycle. A cycle reference value in a period is determined, and thereafter, each time the Karman vortex flow rate detection unit transmits a Karman vortex signal, the cycle measurement value measured by the pulse cycle measurement counter exceeds the cycle reference value by more than 1 and is a predetermined constant of less than 2. , The cycle measurement value exceeds the first reference value, and the cycle measurement value obtained by multiplying the cycle reference value by a predetermined constant of more than 2 and less than 3 is compared with the first reference value. If the value does not exceed the second reference value, a process of adding 1 to the number of pulse signals transmitted by the Karman vortex flow rate detection unit is performed. If the value exceeds the second reference value, the period measurement value and the Kalman vortex signal at this time are added. When the reference cycle timer counts up the sampling cycle, the microcomputer calculates a flow rate calculation program called from the ROM when the reference cycle timer counts up the sampling cycle. A Kalman vortex flowmeter having a process for obtaining a flow value during a sampling period by dividing an integrated value of the number of eddy signal transmissions. 2. A process of calculating a reference cycle, which is performed in the course of execution of the cycle measurement program, determines whether or not the count number of the pulse number counter has reached a value set in advance as the number of measurement cycle values used in the reference cycle calculation. Is determined, and if the set value is not reached, the process immediately returns to the calling cycle measurement program.If the set value is equal, the average value of the cycle measurement values stored in the first cycle buffer is obtained by calculation. Is the value of the provisional reference cycle, and 2
The discriminant value obtained by multiplying by a constant coefficient less than and the cycle measurement value stored in the leading cycle buffer are sequentially compared.If the value of the leading cycle buffer exceeds the above discrimination value and a pulse omission is recognized, the integration cycle The period measurement value at the time of this pulse omission is subtracted from the integrated value stored in the counter, and a temporary reference period value close to the true value is added instead. When the omission detection correction process is completed, the value obtained by dividing the value of the correction integration period by the value of the number of detected pulses is used as the reference period value, and the process returns to the calling period measurement program. The Karman vortex flowmeter according to claim 1, wherein 3. The process of calculating a reference period, which is performed in the course of execution of the period measurement program, is such that each time a Karman vortex signal pulse is input from the Karman vortex flow rate detection unit, a period measurement value measured by the signal pulse is used up to the previous time. Compared with the period measurement value measured by the Karman vortex signal pulse input, the permutation process is performed so that the measurement values are arranged in order of magnitude, and for each permutation process, the minimum period measurement value exceeds 1 and is less than 2 The first reference value obtained by multiplying by the constant is compared with the current cycle measurement value. If the current cycle measurement value exceeds the first upper limit, the minimum cycle measurement value exceeds 2 and is less than 3 Is compared with the current cycle measurement value. If the current cycle measurement value exceeds the second upper limit value, the current cycle measurement value is calculated from the integrated value of the cycle measurement values. , And subtract 1 from the integrated value of the input pulse. If the current cycle measurement value exceeds the first upper limit value but does not exceed the second upper limit value, 1 is added to the integrated value of the input pulse, and the above processing is performed at a predetermined value where the integrated value of the input pulse is a predetermined value. 2. The process according to claim 1, wherein, when repeated until a value is reached, a process of dividing the integrated value of the cycle measurement value by the integrated value of the input pulse to obtain a reference cycle, and then returning from the reference cycle calculation. Karman vortex flowmeter.