JP3216766B2 - 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 an obstacle is placed in a columnar shape in the flow of a fluid, vortices are alternately generated from both ends of the obstacle orthogonal 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 rate detection unit is detected and measured, the transmission unit is provided with an area for storing the output values in the order of output in the RAM. 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 of a predetermined ratio or more from the reference value is detected, 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 "missing pulse" occurs, the process of calculating and outputting the flow rate value based on the frequency value is invalidated, and a small-capacity storage area in which an incorrect flow rate measurement result is not output is provided. An object of the present invention is to provide a transmission section of a Karman vortex flowmeter configured to 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.
Nothing is different.

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
It 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. When the Karman vortex flow rate detection unit sends a Karman vortex signal, it is involved in the period measurement called by the microcomputer from the ROM. The program checks the number of measurement cycle values stored in the first cycle buffer area set in the RAM, and when the number of stored data reaches a predetermined number, determines the cycle in the sampling period based on the stored value of the measurement cycle. Each time the Karman vortex flow detection unit transmits a Karman vortex signal, the cycle reference value is compared with the value of the cycle measured by the pulse cycle measurement counter, and the value of the measurement cycle is determined as the cycle reference value. Only when the ratio does not exceed a predetermined ratio, a processing procedure for integrating this period measurement value and the number of transmitted Karman vortex signals is provided. When you count up the period, RO
A process for calculating the flow rate of the Karman vortex flow rate detection unit during the sampling period by dividing the integrated value of the number of transmitted Karman vortex signals by the integrated value of the period measurement value obtained by the above into the flow rate calculation program called by the microcomputer from M Set up procedures.

[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 value of the measurement period does not exceed a predetermined constant ratio of the period reference value. Only this cycle measurement value and the number of transmitted Karman vortex signals are integrated, so when the reference cycle timer counts up the sampling cycle, the cycle measurement value The integrated value of the pulse signal originating number and thus being excluded data when the "missing pulse" occurs.

[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) which is 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. Corresponding buffer areas NB and TTB are secured. When the integrated value TTC of the pulse period integration counter exceeds the predetermined upper limit MTC, the RAM 7 stores a measurement end flag (ED) indicating the end of the integration for ending the integration of the pulse interval measurement results.
F) and a period measurement flag (PT) indicating whether the process of measuring and integrating the pulse interval is being executed or is in standby.
F) is also secured and set.

Further, the RAM 7 has a reference period timer 5.
Is provided with a sampling time counter (STC) for storing a count value to be counted in determining the flow rate measurement cycle, and this sampling time counter (STC) is provided.
Is set to a value sufficiently longer than the cycle of the output pulse transmitted by the vortex flow rate detector within a range that can follow the time variation of the flow rate in order to maintain the measurement accuracy of the flow rate.

Next, FIGS. 2 to 5 show the flow of one embodiment of the arithmetic processing program executed by the microcomputer 3 based on the first invention of the present application. The operation of the shape will be described.
The Karman vortex flow type transmission unit 2 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, the interrupting process by the 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 caused by the output pulse of the detector when there is an interruption by the output pulse of the Karman vortex flow detector 1 (P1). , P2), PTF
Is 0, indicating that the pulse interval is not being measured,
In order to measure the period from this input pulse to the next input pulse, the count value PPC of the pulse period measurement counter 6 was initialized and started (P3), and the pulse number counter NP and the pulse period integration counter TTC were initialized. Later (P
4) The period measurement flag PTF is set to 1 indicating that measurement is in progress (P5). Interruption due to the output pulse of the Karman vortex flow rate detector 1 is permitted (P6), and the process returns 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 cycle measurement buffer TB (NP), the cycle measurement counter 6 is initialized (P9), and the transferred measurement cycle counter value TB 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
(r) is stored and initialized (P12), and the transferred measurement cycle counter value TF (r) is added to the stored value TTC of the pulse cycle integration counter (P13). A correction process is performed (P14).

After completion of the above-described reference cycle calculation or pulse omission determination correction processing, the stored value of the stored value TTC of the pulse cycle integration counter is compared with a predetermined upper limit set value MTC of the pulse cycle integration value (P15), and TTC Does not exceed the MTC, the interruption by the output pulse of the Karman vortex flow rate detection unit 1 previously masked is permitted (P6) and the interruption is returned (P17), and the pulse cycle integration TTC becomes equal to the upper limit set value MTC. If exceeded, measurement end flag EDF
Is set to 1 indicating the end of measurement (P16), and the process returns from the interrupt without permitting the interrupt (P17).

Subsequently, the cycle reference value calculation processing program called in the cycle measurement program started by interruption by the output pulse of the Karman vortex flow rate detector 1 is used to determine the number SP of data used to determine the cycle reference value. 3 will be described with reference to FIG. The reference period calculation processing program of the embodiment of FIG. 3 is called when the count number NP of the pulse number counter is 3 or less as the value of the initial sampling data number SP in step P11 of the period measurement program. The count number NP of the pulse number counter is S
It is determined whether or not the value of P has reached 3 (R1). If it is not 3, the program immediately returns to the calling cycle measurement program (R10). If it is equal to 3, the first three data of the pulse cycle measurement result are obtained. Period measurement buffer TB (1), TB
The period measurement values stored in (2) and TB (3) are compared with each other, and the average value TR of the remaining two data excluding the maximum value data TM is obtained and determined as the period reference value TR (R
2 to 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 ×
When the value exceeds TR, occurrence of "pulse missing" is recognized. Therefore, the integrated cycle counter holding 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 2 in the above processing
The value of the constant C is set to, for example, 1.5 or the like in order to stably and reliably detect missing one pulse.

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

When called, the pulse missing discrimination correction processing program first sets the cycle value TF (r) measured by the current output pulse of the Karman vortex flow rate detecting unit 1 to a reference value TR of less than 2. C × T multiplied by the coefficient C of
Compared to R (E1), if the measurement period TF (r) is less than this value, the process immediately returns to the calling source (E3). Value of the integrated period counter TT to invalidate the measurement result of
While subtracting the value TF (r) of the current measurement cycle from C,
After subtracting one count from the count number NP of the pulse number counter (E2), the process returns to the calling source (E3). Note that the value of the constant C less than 2 in the above processing is set to, for example, 1.5 in order to stably and reliably detect missing one pulse as in the reference cycle calculation processing.

According to the cycle measurement program described above, the cycle reference value T excluding "pulse missing" is obtained by using a plurality of cycle measurement data obtained at the beginning of the sampling cycle.
When R is set, when there is an interruption due to the output pulse of the Karman vortex flow detecting unit 1, data in which a pulse omission has occurred based on this value is excluded, and when the sampling cycle ends, the pulse number counter is stored. As the value NP and the stored value TTC of the integration period counter, data excluding "pulse omission" 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. 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 (NPB) 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 measurement end flag (EDF) test result is completed, the measurement end flag (EDF)
And the pulse period measurement flag (PTF) are 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). The interruption by the output pulse of the flow rate detecting unit 1 masked in the step (1) 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 for directly setting the flow rate value Q to 0 is performed (S9). 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, the pulse omission occurs accidentally and independently even if it occurs. 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 SP value 3 (K
1) If it is not 3, the program immediately returns to the caller's cycle measurement program (K10). If it is equal to 3, the first three data of the pulse cycle measurement result are used as cycle measurement buffers TB (1), TB (2), And the average value of the period measurement values stored in TB (3) is calculated, and this is calculated as the value T of the temporary reference period.
RI (K2). Then, the value TR of this provisional reference cycle
A value C × TRI obtained by multiplying I by a constant coefficient C less than 2 is sequentially compared with a cycle measurement value TB (i) (i = 1, 2, 3) stored in the cycle measurement buffer, and TB (i) If the value exceeds the above discrimination value and a pulse dropout is recognized, the cycle measurement value TB (i) at the time of this pulse dropout is subtracted from the integrated value TTC stored in the integration cycle counter, and a temporary value closer to the true value is obtained. The reference cycle value TRI is added to obtain a new integration cycle value TTC (K3 to K8).

When the above-described pulse missing detection correction processing based on the cycle measurement value comparison is completed, the value obtained by dividing the correction integration cycle value TTC by the detected pulse number value 3 is set as the reference cycle value TR, and the calling source is calculated. (K10). In addition, when "pulse missing" occurs during the measurement of the cycle that determines the reference cycle of the first Karman vortex signal pulse in each sampling cycle, the measurement result is deleted and a correct measurement value that does not include "pulse missing" is obtained. FIG. 7 shows a flow of an embodiment of a reference period calculation program by processing based on the third invention for repeating measurement, 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.

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 detection unit 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 permutation 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). C × TB (1) multiplied by the coefficient C and the maximum period measurement value T
B (3) is compared with (T10). If the value of TB (3) does not exceed the above discrimination value and "pulse missing" is not recognized, the minimum value TB of the cycle measurement values replaced in ascending order After the average value of (1) and the next largest value TB (2) is set as the reference period value TR (T11), the process returns from the reference period calculation (T14).

On the other hand, the value of TB (3) is equal to the discrimination value C × T
If B (1) is exceeded, "pulse missing" is recognized, so the value TB (3) of the third measurement cycle is subtracted from the accumulated cycle counter holding value TTC to invalidate the measurement result, and the pulse After subtracting one count from the count number NP of the number counter (T9), the value TB of the second measurement cycle
After the same inspection process is performed for (2) (T12), the process returns from the reference cycle calculation (T14).

According to the processing of the flow of FIG. 7 described above, when a missing pulse is detected, the count number NP of the pulse number counter is decremented. In the embodiment, it is repeated three times.

[0035]

In the transmission section of the Karman vortex flow meter according to the present invention, the measurement cycle counter area for storing the measured value output value of the pulse cycle measurement counter cannot store all the measured values, Set a narrow area where only data can be stored, and when a predetermined number of pulse period measurement values are obtained, determine a reference period in the sampling period based on the obtained pulse period measurement values. Each time the pulse period of the output pulse of the detector is measured by the pulse period measurement counter, this measured value is compared with the value of the reference period, and only when the value of the measurement period does not exceed a predetermined ratio of the value of the reference period. Since the cycle measurement value and the generation of one Kalman vortex signal are integrated in the integration cycle counter and the pulse number counter, "pulse missing" occurs when the sampling period ends. The measured value from which the influence is excluded remains in the integration period counter and the pulse number counter, and the flow rate can be directly calculated based on the measured value. The effect of obtaining a Karman vortex flowmeter that outputs a flow value can be 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 determine 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 close to the true value instead to obtain a new integration cycle value is as follows.
Since the simple processing is repeated, the processing speed is high, the time variation of the flow rate is severe, and the sampling cycle is effectively adapted to a target to be set short.

On the other hand, each time a Karman vortex signal pulse is input, the value of the measurement cycle measured by the signal pulse is compared with the value of the measurement cycle measured by the previous input of the Karman vortex signal pulse, and the measured value is calculated. After performing the swapping process so that are arranged in the order of the size, the missing pulse is inspected,
According to the reference cycle calculation program for subtracting the result of the measurement from the value held by the integration cycle counter and the count number of the pulse number counter to invalidate the measurement result when the missing pulse is recognized, Period measurement for obtaining the reference period is repeated until a predetermined number of period measurement data are not obtained, so that an accurate reference period value can be reliably obtained, and the streamline distribution is unstable, causing a pulse omission. The effect is obtained that the method can be effectively applied to a measurement object or the like in which noise is easily generated.

[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 a flow detection unit output pulse interrupt;

FIG. 3 is a flowchart of a program for obtaining a reference cycle.

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

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

FIG. 6 is a flowchart of a program according to another embodiment for obtaining a reference cycle.

FIG. 7 is a flowchart of a program according to another embodiment for obtaining a reference cycle.

[Explanation of symbols]

 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 cycle counter TTC Integration cycle counter TTB Integration cycle buffer STC Sampling cycle counter TR Reference cycle TRI Temporary reference cycle TM Maximum measurement cycle MTC 8 ROM 81 Cycle 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 period measurement program checks the number of measurement period values stored in the leading period 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 period. A cycle reference value in the period is determined, and thereafter, each time the Karman vortex flow detection unit transmits a Karman vortex signal, the cycle reference value is compared with the value of the cycle measured by the pulse cycle measurement counter. Only when the predetermined ratio of the reference value does not exceed a predetermined ratio, a processing procedure is provided for integrating this period measurement value and the number of transmissions of the Karman vortex signal. When the sampling period is counted up, the flow rate calculation program called by the microcomputer from the ROM is divided by the integrated value of the Karman vortex signal transmission number by the integrated value of the cycle measurement value obtained as described above, and the flow rate value in the sampling period A Karman vortex flowmeter, characterized by having a processing procedure for obtaining vortex flow. 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. If the set value has not been reached, the process immediately returns to the caller's cycle measurement program.If it is equal to the set value, the average value of the cycle measurement values stored in the first cycle buffer is calculated. 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 first cycle buffer are sequentially compared. If the value of the first 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. Of the Kalman vortex signal pulse input, and performs permutation processing such that the measured values are arranged in ascending order, for example, in ascending order. When the permutation processing is completed, the minimum period measurement value is less than 2 Compare the discriminant value obtained by multiplying by the constant coefficient with the maximum period measurement value at the end of the permutation.If the maximum period measurement value does not exceed the above discrimination value and no pulse omission is recognized, ascending order If the average value of the minimum value of the cycle measurement value and the next largest measurement value replaced with is used as the reference cycle value, the process returns from the reference cycle calculation, and if the maximum value of the cycle measurement exceeds the above discrimination value, Is In order to invalidate the result, the maximum cycle measurement value is subtracted from the accumulated cycle counter hold value, and one count is subtracted from the count number NP of the pulse number counter, and then the same inspection processing is performed for the next-order cycle measurement value. 2. The Karman vortex flowmeter according to claim 1, wherein the process is a process of returning from the reference cycle calculation after the process.