JP3348563B2 - 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 output control means for a Karman vortex flow meter for measuring the 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 uses a Karman vortex sensor consisting of a piezoelectric element that captures slight pressure fluctuations of the fluid when vortices are generated by obstacles, and a weak signal output by the Karman vortex sensor. Amplifying, and a waveform shaping circuit that outputs a pulse signal of a constant waveform when this value exceeds a certain threshold is provided, and a Karman pulse signal of a frequency corresponding to the flow rate of the fluid is provided from the Karman vortex flow rate detection unit. Be sent.

[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]

A flow detector of a Karman vortex flowmeter amplifies a weak signal output from a Karman vortex sensor and outputs a shaped pulse signal having a constant waveform when the amplified signal exceeds a certain threshold. Therefore, when the output signal of the Karman vortex sensor decreases due to factors such as “fluctuation” of the fluid flow and falls below the threshold, “pulse missing” in which a shaped pulse signal is not transmitted may occur.

When the "pulse missing" occurs, the transmission unit according to the above-mentioned prior art counts the total number of input pulse signals smaller by the amount of the "pulse missing", so that the frequency obtained by the calculation is the frequency of the actual Kalman pulse. The frequency becomes lower and a large error occurs in the flow measurement output value. The present invention, when "pulse missing" occurs, invalidates the process of calculating and outputting the flow rate value based on the frequency value,
It is an object of the present invention to provide a transmission section of a Karman vortex flowmeter that does not output an incorrect flow measurement result and improve the reliability of flow measurement by the Karman vortex flowmeter.

[0006]

A transmission section of a Karman vortex flowmeter receives an output pulse signal of a flow detection section of a Karman vortex flowmeter during a sampling period for recording flow measurement data, and a time interval between the pulse signals. The measurement of the time interval between the pulse signals is not completed because the pulse signal for terminating the measurement of the time interval between the pulse signals is not input from the flow rate detection unit during the period of the sampling cycle even though the measurement of the pulse signal is started. Occasionally, the flow rate is almost zero or "pulse missing" occurs, and no pulse signal is transmitted from the flow rate detection unit.

Therefore, in order to prevent the occurrence of an error due to "pulse omission" 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 pulse period measurement counter for measuring a time interval between pulse signals transmitted by the Karman vortex flow detector, and a pulse period measurement counter for measuring a transmitted pulse signal of the Karman vortex flow detector to obtain a flow rate. A fixed-period timer that gives a sampling period as a time interval for executing arithmetic processing, a time counter between pulse signals measured by a pulse number counter that counts the number of pulse signals transmitted by the Karman vortex flow detector and a pulse signal that is measured by a pulse period measurement counter An integration cycle counter that integrates and stores it each time Black computer has set the area temporarily storing a code (flag) and the count value that represents the state in which temporary storage is required in the calculation process of the process of executing R
It comprises an AM, a ROM storing a program for an arithmetic processing executed by the microcomputer, and an output unit for outputting a result of the arithmetic processing.

When the fixed period timer counts up the sampling period, the microcomputer calculates the flow rate from the ROM and executes the flow rate calculation program. Although the pulse signal is received and the measurement of the time interval between the pulse signals is started, a pulse signal for terminating the time interval measurement between the pulse signals during the sampling period is input from the Karman vortex flow rate detection unit. If the time interval measurement between pulse signals is not completed, it is determined that "pulse missing" has occurred and the flow rate detection value in the previous sampling cycle is held, and in other cases, the flow rate value is set to zero A pulse missing discrimination process is provided, and the pulse number counter and the integration period are used during a sampling period. To determine a flow rate of the fluid in the sampling period by the calculation in the counter area by acquiring the stored data.

[0009]

In the transmission section of the Karman vortex flowmeter according to the present invention, each time the flow detection section transmits a pulse signal, the pulse number counter is incremented and the number of pulses is counted. It is measured by the measurement counter and integrated by the integration period counter. Then, although the pulse missing determination process of the flow rate calculation program executed when the fixed cycle timer counts up the sampling cycle starts measuring the time interval between pulse signals by the transmitted pulse signal of the flow rate detection unit. When the pulse signal is not input from the flow rate detector and the time interval measurement between pulse signals is not completed during the sampling period, it is determined that "pulse missing" has occurred and the previous sampling is performed. The flow rate detection value in the cycle is held, and in other cases, the flow rate value is set to zero. Then, the flow rate of the fluid in the sampling cycle is calculated by the data stored in the pulse number counter area and the integration cycle counter area during the sampling cycle.

[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 device including a Karman vortex sensor for generating a signal having a frequency proportional to the flow velocity of a fluid, and a waveform shaping circuit for amplifying and shaping a weak signal generated by the Karman vortex sensor and outputting the signal. Department.

Reference numeral 2 denotes a transmission unit including the following 3 to 9 components for receiving a Karman vortex pulse signal transmitted from the flow detecting unit 1 as an input signal, calculating and outputting a flow value. In the transmission measuring unit 2, a microcomputer 3 receives the output pulse signal of the Karman vortex flow detecting unit 1, performs a calculation for obtaining the flow rate, and performs a process of outputting the calculation. Step operation.

Reference numeral 5 denotes a constant cycle timer (SCT) for generating an execution cycle of the measurement calculation processing performed by receiving the output pulse signal of the Karman vortex flow rate detection unit 1 by dividing the clock signal of the system clock 4. 6 is activated by a pulse signal transmitted by the Karman vortex flow rate detecting unit 1 as a trigger, and measures a time interval until a next pulse signal is input by counting clock signals of the system clock 4, and When a pulse signal is input and the measured value up to this time is transferred to the microcomputer 3, the pulse interval measurement counter is restarted to measure the time interval until the next pulse arrives. The output signal is input to the pulse interval measurement counter 6 via an interrupt input terminal INT2 relating to pulse frequency measurement of the microcomputer 3. That.

The ROM 8 is a read-only storage unit in which the operation process of the microcomputer 3 is stored. In the storage program, the periodic request timer 5 counts up and the interrupt request signal INT1 is input to the microcomputer 3. In this case, a fixed-period interruption program (81) that is called to perform an operation for obtaining the flow rate, and that when the flow rate detection unit 1 transmits a pulse, this is transmitted as an interrupt signal INT2
And a period measurement program (82) started as a program.

The RAM 7 is a storage means that can be written and read as needed to temporarily store a code (flag) and a count value indicating a state that requires temporary storage during the execution of the arithmetic processing of the microcomputer 3. A pulse number counter (NPC) is provided in the storage area of the RAM 7 for counting the output pulses each time the flow rate detection unit 1 transmits an output pulse.
Each time the pulse period measurement counter 6 measures and transmits the time interval between subsequent pulses, an integration period counter (TTC) that accumulates and stores this value is secured. During execution of the arithmetic output processing, buffer areas (NPB, TTB) corresponding to the respective counters for temporarily holding the values stored in the respective counters are secured. The RAM 7 stores a measurement end flag (EDF) indicating the end when the integration of the pulse interval measurement result is completed because the integrated value TTC of the pulse cycle integration counter exceeds the predetermined upper limit MTC, and a flow rate. A pulse interval measurement flag (PSF) indicating whether or not a pulse signal is input from the detection unit 1 and the process of measuring and integrating the pulse interval is started.
In addition, when "pulse missing" is detected in the process of the fixed-period interrupt program (81), an area for storing a pulse missing determination flag (PDF) for displaying this is also set.

Next, FIGS. 2 to 4 show the flow of an embodiment of an arithmetic processing program executed by the microcomputer 3 based on the present invention, and the operation of the Karman vortex flowmeter of the present invention will be described with reference to these drawings. Will be described. In the Karman vortex flowmeter according to the present invention, the flow detector 1 transmits only a single pulse signal and starts measuring the inter-pulse period during one sampling period determined by the fixed period timer 5, but the end of one period. When the indicated pulse signal is not transmitted from the flow rate detection unit 1, it is interpreted that "pulse missing" has occurred, and the detection value in this sampling cycle is invalidated.
The flow measurement value in the previous sampling cycle is continuously output.

The transmission section 2 of the Karman vortex flowmeter according to the present invention illustrated in FIG. 1 sets the interruption from the fixed-cycle timer 5 to the higher rank and sets the fixed-cycle timer 5 when the standby is set after the initial conditions are set. It enters an interrupt standby state in which an interrupt caused by an output pulse of the flow rate detector 1 that occurs at a shorter time interval than the sampling cycle is set as a lower order. When the fixed-cycle timer 5 counts up the sampling time and an interrupt request is input from the fixed-cycle timer 5 to the interrupt request terminal INT1 of the microcomputer 3, the ROM 8 reads the interrupt request from FIG.
The fixed-period timer interrupt program (81) of the flow of (1) is called and activated (S0).

As shown in FIG. 2, the fixed-period timer interrupt program (81) first masks the interrupt caused by the output pulse of the flow rate detector 1 when it is started, and sets the measurement end flag (EDF) to Check the status (S1, S
2). When the value of the measurement end flag (EDF) is 1 and the end of the measurement of the pulse period is indicated, the measurement values stored in the pulse number counter (NPC) and the integration period counter (TTC) are subjected to the flow value calculation process. In this case, the data is transferred to buffers (NPB, TTB) provided corresponding to the respective counters (S3), and the pulse missing flag (PDF) is set to "1" to start the next sampling cycle. It is set to 0 indicating no "pulse missing" (S4).

On the other hand, the value of the measurement end flag (EDF) is 0
If it is indicated that the period measurement between pulses transmitted by the Karman vortex flow detector has not been completed as it is,
The process proceeds to the pulse missing determination process (S5). When the processing based on the inspection result of the measurement end flag (EDF) is completed, 0 is set in each of the measurement end flag (EDF) and the pulse period measurement flag (PSF), and the period measurement of the output pulse signal of the flow rate detector 1 is performed. Is not started and not yet finished (S6), and the interruption by the output pulse of the flow rate detector 1 masked earlier is permitted (S6).
7). Therefore, when this processing is completed, the transmission unit 2 sets the interruption from the fixed-cycle timer 5 to the higher order, and
It returns to the interrupt waiting state in which the interrupt by the output pulse is set as the lower order.

Subsequently, the stored value NP of the pulse number buffer
B is checked (S8), and when this value is 0, a process for directly setting the flow rate value Q to 0 is performed (S10), and when NPB is not 0, the pulse number buffer (NPB) and the integration period buffer (TTB) are first. Flow detection unit 1 that has been transferred and saved
Performs a calculation for obtaining the flow value Q using the number of pulse signals transmitted by the controller and the integrated value of the inter-pulse period (S9), outputs the obtained flow value Q (S11), and returns from the fixed period timer interrupt. .

Next, an interruption process by an output pulse of the flow rate detecting section 1 will be described. When the output pulse of the flow rate detector 1 is input to the interrupt request terminal INT2 of the microcomputer 3, the cycle measurement program (82) of the flow in FIG. 3 is called out and the process is performed (K0). When there is an interrupt due to the output pulse of the flow rate detecting unit 1, the cycle measurement program (82) temporarily masks the interrupt due to the output pulse and checks the state of the pulse cycle measurement flag (PSF) (K
1, K2), when the PSF is 0 indicating that the pulse interval measurement has not been started, the count value PCC of the pulse period measurement counter 6 is initialized to measure the period from this input pulse to the next input pulse. And start (K
3) After the pulse number counter (NPC) and the pulse period integration counter (TTC) are also initialized (K4), the pulse period measurement flag (PSF) is set to 1 indicating that measurement is in progress (K5). The interrupt by the output pulse is permitted (K6) and the process returns from the interrupt (K12).

On the other hand, when the pulse period measurement flag (PSF) indicates 1 during the measurement, the stored value NPC of the pulse number counter is incremented (K7), and the measured value PCC of the pulse period measurement counter 6 is integrated in the pulse period. The value is added to the value TTC stored in the counter to obtain a new TTC value (K9). Then, the stored value TTC of the new pulse period integration counter is compared with a lower limit set value MTC of the pulse period integration value, which is set in advance as a large value within a range allowed by the sampling period so that the frequency can be obtained with a required resolution. (K10), if TTC does not exceed MTC,
The interrupt by the output pulse of the flow rate detection unit 1 that has been previously masked is permitted, and the process returns from the interrupt (K6, K1).
2) If the TTC exceeds the MTC, after the measurement end flag (EDF) is set to 1 indicating the end, the process returns from the interrupt without canceling the interrupt mask by the output pulse of the flow rate detector 1 (K11). , K12).

With the above-described processing, each time an interrupt is generated by a pulse signal from the flow rate detecting section 1, the number of pulses transmitted from the flow rate detecting section 1 is stored in the pulse number counter (NPC). The time interval is measured as a pulse cycle by the pulse cycle measurement counter 6, and the measured value PCC of the cycle is integrated in the pulse cycle integration counter (TTC).

Based on the above-described processing at the fixed-period timer and the interruption from the flow rate detector 1, the pulse missing determination processing of the flow illustrated in FIG. 4 which is the basis of the present invention will be described. In the pulse missing determining process of the flow of FIG. 4, the fixed-cycle timer 5 counts up the sampling time and sends an interrupt request to the microcomputer 3 as already mentioned in the description of the fixed-cycle interrupt program (81) in FIG. In the course of the processing executed by the fixed-period timer interrupt program (81) started when this occurs, the period measurement between the pulses transmitted by the flow rate detector 1 has been completed while the value of the measurement end flag (EDF) remains 0. It is called when it is indicated that there is no data (S5).

Incidentally, the measurement end flag (EDF) is
As mentioned in the description of the period measurement program (82),
When the integrated value of the period between the pulses transmitted by the flow rate detection unit 1 exceeds a lower limit set value MTC set in advance as a large value within a range permitted by the sampling time set in the fixed period timer 5, it indicates that the measurement is completed. Can be set up. Therefore, even though the sampling time has elapsed, the integrated value of the period between pulses does not exceed the lower limit set value MTC, and the value of the measurement end flag (EDF) remains 0 indicating that measurement has not been completed. If the fluid is not flowing through the flow detecting unit 1, the flow rate is almost zero even if it flows, or "pulse missing" occurs, and a pulse signal that should raise the measurement end flag (EDF) is transmitted from the flow detecting unit 1. This means that the status has not been set.

Therefore, in the pulse missing determination processing, first, the pulse period measurement flag (PSF) is checked (E1) PS
When F remains at 0, the flow rate detection unit 1 does not transmit any pulse during this sampling period, so that "missing pulse" should not occur, so that the "missing pulse" is set in the missing pulse determination flag (PDF). Set 0 to indicate none (E
2), it is determined that the fluid is not flowing through the flow rate detecting section 1 and a zero value is written into the pulse number buffer NPB and the integration cycle buffer TTB (E5).

On the other hand, if the pulse period measurement flag (PSF) is 1, indicating that at least one pulse has been input from the flow rate detection unit 1, the measurement end flag (ED
In order to determine whether F) is not set to 1 on the end side because the flow rate of the fluid is almost 0 or "pulse missing" has occurred, the pulse missing determination flag (PDF) is inspected. (E3) When the PDF remains at 0 set in the step S4 of the fixed-cycle timer interrupt process at the start of the sampling cycle, the flow rate detection unit 1 is set to the time at which the measurement end flag (EDF) should be raised in the current sampling cycle. It is determined that a “pulse missing” in which no transmitted pulse is detected has occurred and the pulse missing determination flag (P
DF) is set to 1 indicating "pulse missing" (E)
4) When 1 is set in the PDF, since the frequency of the pulse signal transmitted by the flow rate detection unit 1 is extremely low even in the previous sampling cycle, the measurement end flag (EDF) is set during the sampling cycle. Although a pulse signal to be set to 1 on the end side was not input, at least one pulse is received from the flow rate detection unit 1 so that 1 indicating "pulse missing" is set in the pulse missing determination flag (PDF). It is determined that the flow rate of the fluid is almost zero, and the zero value is written to the pulse number buffer NPB and the integration period buffer TTB so that the flow rate measurement result becomes zero (E5).

Setting of the above-mentioned pulse missing determination flag (PDF) (E4) or writing a zero value to the pulse number buffer (NPB) and the integration period buffer (TTB) (E5)
When any of the processes is completed, the process returns from the pulse missing determination process (E6). If "pulse missing" occurs for the first time in this sampling period, the pulse number buffer (NPB) and the integration period buffer (TTB) are stored in the previous time. Since the data measured in the sampling period is held, the flow rate calculation result to be output holds the measurement value in the previous sampling period. on the other hand,
If no pulse is received from the flow rate detector 1 or a pulse is received over two or more sampling periods, but the measurement end flag (EDF) is not set to 1 on the end side, and a pulse missing judgment is made. When the flag (PDF) is set to 1 indicating occurrence of "pulse missing", the state where the flow rate of the fluid is zero or almost zero continues, and the frequency of pulse transmission from the flow rate detection unit 1 is extremely low. The transmission unit outputs a measurement result with a zero flow rate.

[0028]

In the transmission section of the Karman vortex flow meter according to the present invention, when the fixed-period timer counts up the sampling period, the microcomputer calculates the flow rate during the sampling period determined by the fixed-period timer. The pulse signal that terminates the time interval measurement between pulse signals during the sampling period despite the fact that the period measurement counter has started measuring the time interval between pulse signals by the transmitted pulse signal of the Karman vortex flow detector is Kalman. If the time interval measurement between pulse signals is not completed without being input from the vortex flow detector, it is determined that "pulse missing" has occurred, and the flow detection value in the previous sampling cycle is held. A pulse missing discrimination process is set to zero, and during the sampling period, Since the flow rate of the fluid in the sampling cycle is calculated by calculation based on the data stored in the pulse number counter area and the accumulation cycle counter area, the flow rate value becomes smaller and the output of the Karman vortex sensor in the flow rate detector becomes smaller. Even in a situation where it is difficult to detect the rise or fall of the signal in the waveform shaping circuit and “pulse missing” occurs, “pulse missing”
The occurrence of erroneous flow measurement results in the previous sampling cycle with less error due to recognition of the occurrence of erroneous flow measurement results is eliminated, and the reliability of flow measurement by the Karman vortex flow meter is improved. The effect is obtained.

[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 program flow chart of a fixed-cycle timer interrupt process.

FIG. 3 is a program flow chart of a flow rate detection unit output pulse interrupt processing;

FIG. 4 is a program flow chart of pulse missing determination processing.

[Explanation of symbols]

 1 Karman vortex flow detector 2 Transmitter 3 Microcomputer 4 System clock 5 Fixed period timer 6 Pulse period measurement counter 7 RAM PSF Pulse period measurement flag EDF measurement end flag PDF Pulse missing judgment flag NPC Pulse number counter NPB Pulse number buffer TTC Integration Period counter TTB Integration period buffer 8 ROM 81 Fixed period interrupt program 82 Period measurement program 9 Output signal converter

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-5-164590 (JP, A) JP-A-60-56220 (JP, A) JP-A-61-96414 (JP, A) Patent 3217661 (JP, A) B2) Patent 3216766 (JP, B2) Patent 3216768 (JP, B2) (58) Fields investigated (Int. Cl. ⁷ , DB name) G01F 1/32

Claims (1)

(57) [Claims] 1. A Karman vortex sensor as a flow detecting end,
A Kalman vortex flow rate detection unit comprising a waveform shaping circuit for shaping an output signal of the sensor into a pulse signal, and a Kalman comprising a transmission unit for performing a calculation and an output process for measuring the output pulse signal of the flow rate detection unit to obtain the flow rate A vortex flowmeter, wherein the transmission unit performs a calculation and an output step process at a timing given by a system clock, and a pulse period for measuring a time interval between pulse signals transmitted by the Karman vortex flow detection unit. A measurement counter, a fixed-period timer for measuring a transmission pulse signal of the Karman vortex flow detection unit by this pulse period measurement counter and providing a sampling period as a time interval for executing a calculation process for obtaining a flow rate, and a Kalman vortex flow detection unit The pulse number counter that counts the number of pulse signals to be transmitted and the pulse Each time the time interval between the pulse signals is output, an accumulation period counter for accumulating and storing the time interval, and a code (flag) and a count value indicating a state requiring temporary storage in the course of arithmetic processing executed by the microcomputer are temporarily stored. A ROM in which an area to be set is set, a ROM storing a program for arithmetic processing executed by the microcomputer, and an output unit for outputting a result of the arithmetic processing, wherein the ROM is used when the fixed-cycle timer counts up a sampling cycle. Although the microcomputer calculates and executes the flow rate calculation program, the period measurement counter receives the pulse signal of the Karman vortex flow rate detector during the sampling period and starts measuring the time interval between the pulse signals. The measurement of the time interval between pulse signals is completed during the sampling period. When the pulse signal to be input is not input from the Karman vortex flow rate detection unit and the time interval measurement between the pulse signals is not completed, it is determined that "pulse missing" has occurred and the flow rate detection value in the previous sampling cycle is held, In other cases, the apparatus includes a pulse omission determination process that sets the flow rate value to zero, and the flow rate of the fluid in the sampling cycle is obtained based on the data acquired and stored in the pulse number counter and the area of the integration cycle counter during the sampling cycle. The Karman vortex flowmeter is characterized in that it is a process for obtaining by calculation.