JPH08110252A - Karman's vortex flowmeter - Google Patents

Abstract

PURPOSE: To simplify a calibrating/testing work when the actual flow rate of a Karman's vortex flowmeter is calibrated, by obtaining a correct, corrected flow rate even if the flow rate of a calibration fluid is not matched to a value of a calibration point. CONSTITUTION: Arm EPROM 9 is provided at a transmitting part 2 of the Karman's vortex flowmeter, which writes and holds values of the flow fate and the correction amount of the flow rate at a flow rate calibration point measured by a reference flowmeter to calibrate/test the actual flow rate. When a linear correction flag indicates to execute a correction operation, namely, when the flag indicates a normal measurement, a measured value of the flow rate obtained by processing an output pulse of a flow rate detection part 1 is linearly interpolated with the use of values of the flow rate and correction amount held in the EPROM 9 thereby to operate and output tone correction amount. If the linear correction flag indicates not to execute the correction operation, that is, when the actual flow rate is to be calibrated/tested, the measured value obtained at the frequency/flow rate operation process is output as it is thereby to obtain the flow rate and correction amount at the flow rate correction point to be written in the EPROM 9.

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 correcting means in a Karman vortex flowmeter 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 orthogonal to the flow direction at a cycle inversely proportional to the flow velocity of the fluid. This is a flow meter that utilizes the phenomenon of The Karman vortex flowmeter uses a Karman vortex sensor consisting of a piezoelectric element that captures slight pulse-like pressure fluctuations of the fluid when an vortex is generated by an obstacle, and a weak pulse output by the piezoelectric element. A waveform shaping circuit that amplifies and outputs the signal is provided, and since the pulse signal of the frequency corresponding to the flow rate of the fluid is transmitted from the flow rate detection unit, the pulse signal transmitted by the flow rate detection unit in the transmission unit. The flow rate of the fluid is measured and output by measuring the frequency or period of the above and performing arithmetic processing.

The frequency of the pulse signal transmitted by the Karman vortex flow rate detection unit is basically proportional to the flow rate of the fluid flowing through the flow rate detection unit, but when high-accuracy flow rate measurement is required, the flow rate reference is set in advance. Flow rate of the flow rate calibration point to the Karman vortex flow rate detection unit using the instrument to obtain the deviation between the detected flow rate value and the reference flow rate value as the flow rate correction amount. Vortex Flow rate is calculated from the pulse signal detected by the flow rate sensor In the process of the calculation process performed by the transmission section, the flow rate measurement value is obtained by directly performing linear correction on the measured value using the previously calculated flow rate correction amount. Is output as.

The linear correction according to the prior art is carried out by using a predetermined flow rate calibration point, for example, a flow rate correction amount obtained by fixing at 25%, 50%, 75% and 100% of the measured full scale. This is the method, and in the actual flow rate calibration test for obtaining the flow rate correction amount, it is necessary to accurately match the flow rate of the calibration fluid flowing to the flow rate detection unit to the flow rate value at the flow rate calibration point for testing.

[0005]

In the test for obtaining the flow rate correction amount for the Karman vortex flowmeter which performs the linear correction calculation process according to the conventional technique described above, the flow rate detecting portion was adjusted to the flow rate at the flow rate calibration point accurately. It is necessary to flow the calibration fluid, but setting this flow rate is a laborious and difficult task, and if the calibration of the flow rate calibration point to the flow rate value is inaccurate, an incorrect flow rate correction amount is determined. Therefore, there is a problem that accurate flow rate measurement cannot be performed even if linear correction calculation processing is performed.

The present invention provides a linear correction calculation processing means which does not require the flow rate of the calibration fluid to be flown to the flow rate detecting section to be accurately matched to the flow rate calibration point in the actual flow rate calibration test for obtaining the flow rate correction amount. It is an object of the present invention to realize a Karman vortex flowmeter capable of highly accurate flow rate measurement while simplifying the calibration test.

[0007]

In order to achieve the above object,
According to the present invention, the linear correction flag indicating the execution / non-execution of the linear correction calculation for the flow rate measurement value in the transmission unit, the flow rate value and the flow rate correction amount at the flow rate calibration point measured by the reference flow meter in the actual flow rate calibration test. , And a memory consisting of an EPROM for writing and holding, and a correction calculation work area for temporarily storing the count value and the mantissa value generated in the linear correction calculation process in the RAM of the microcomputer. Then, when the transmission unit performs the calculation process of measuring the output pulse signal of the flow rate detection unit to obtain the flow rate, if the linear correction flag indicates the linear correction calculation, the output pulse of the flow rate detection unit is set to the frequency. -For the flow rate measurement value obtained by the flow rate calculation processing, the EPROM is used.
If the linear correction flag does not instruct the linear correction calculation, the correction value is calculated and output by linear interpolation using the flow rate value and the value of the flow rate correction amount read from the flow rate calibration point. The Karman vortex flowmeter is configured so that the output pulse is processed as it is and the flow rate measurement value obtained by the frequency / flow rate calculation processing is output.

[0008]

[Function] With the EPROM having a data holding function regardless of the presence or absence of the power source, the flow rate and the corrected flow rate value at the flow rate calibration point obtained in the actual flow rate calibration test of the Karman vortex flowmeter are held, and the linear correction flag is linearly calculated. In the case of the flow rate measurement mode set to execution, the flow rate measurement value obtained by frequency / flow rate calculation processing of the output pulse of the flow rate detection unit is applied to both the flow rate at the calibration point read from the EPROM and the corrected flow rate. The correction value is calculated and output by linear interpolation using the value.

On the other hand, in the case of the actual flow rate calibration test in which the linear correction flag is set to the non-execution of the linear correction calculation, the flow rate measurement value obtained by performing the frequency / flow rate calculation processing on the output pulse of the flow rate detection unit is output as it is. Therefore, from this flow rate measurement value and the reference flow rate value indicated by the reference flow rate meter used in the actual flow rate calibration test, the flow rate value and the corrected flow rate value at the calibration point to be written and stored in the EPROM can be obtained.

[0010]

FIG. 1 shows a schematic structure of an embodiment of the Karman vortex flowmeter according to the present invention. In FIG. 1, reference numeral 1 denotes a flow rate detection unit including a Karman vortex sensor that generates a pulse signal at a period that is inversely proportional to the flow velocity of a fluid, and a waveform shaping circuit that amplifies and outputs the pulse signal of the Karman vortex sensor. .

Reference numeral 2 is a transmission unit for calculating and outputting a flow rate value using the Karman vortex pulse signal transmitted by the flow rate detecting unit 1 as an input signal. In this transmission measurement unit 2,
Reference numeral 3 is a microcomputer that receives the output pulse signal from the vortex flow rate detection unit 1 and performs a process of calculating and outputting the flow rate. Reference numeral 4 is an output pulse signal from the Karman vortex flow rate detection unit 1. It is a reference period timer that determines the basic unit of the period of the measurement calculation process to be performed, and the execution timing of each step of the measurement calculation is determined based on the unit period given by this timer.

Reference numeral 5 is a pulse interval measurement counter for measuring the time interval between the pulse signals transmitted by the flow rate detection unit 1, and this pulse interval measurement counter is provided for each measurement calculation processing cycle determined by the reference cycle timer. The frequency of the pulse in the measurement calculation processing cycle can be obtained by the cumulative value of the time intervals between pulses measured in 1 and the number of measured pulses.

The ROM 8 is a read-only storage means in which the operating process of the microcomputer 3 is stored, and the storage program samples the output pulse signal of the flow rate detection unit 1 every measurement calculation processing cycle and this cycle is used. A frequency / flow rate measurement program that calculates the flow rate by measuring the frequency of the pulse signal at
It contains an output program that displays and outputs the flow rate value based on the flow rate measurement results.

The RAM 7 is a RAM serving as a storage means capable of writing / reading at any time for temporarily storing codes (flags) and count values that need to be temporarily stored during the execution of the arithmetic processing of the microcomputer 3. And 6
Is a setting device for setting and inputting a constant value, an operating condition, and the like relating to the measurement target to the transmission unit 2 of this Karman vortex flowmeter.

On the other hand, reference numeral 9 indicates the values of the flow rate and the corrected flow rate at the flow rate calibration points determined by the actual flow rate calibration test of this Karman vortex flowmeter, and the execution or non-execution of the linear correction operation of the flow rate performed using these values. Is an EPROM which holds the state of the linear correction flag indicating the switching of the above and retains it regardless of the presence or absence of the power supply. Next, in FIG.
Shows the flow of the basic operation of the Karman vortex flowmeter as an example. First, the basics of this Karman vortex flowmeter operation will be described with reference to this figure, and then the steps of the actual flow rate calibration test will be described.

The transmission section 2 of the Karman vortex flowmeter according to the present invention illustrated in FIG. 1 sets the interrupt from the reference period timer 4 as the higher order when the initial condition is set and the standby state and the output of the flow rate detection section 1 Enters the interrupt standby state with lower interrupts. Then, when the reference period timer 4 counts up, it is determined whether or not the sampling period set as a multiple of the reference period has elapsed. If it is determined that the sampling time is not reached, the interrupt is immediately returned to wait for the sampling time to elapse. When the state is continued and it is determined that the sampling time has elapsed, the next frequency / flow rate calculation processing program is executed.

In the frequency / flow rate calculation process, the frequency of the pulse signal transmitted by the Karman vortex flow rate detection unit during the sampling period is calculated based on the measured value by the pulse interval measurement counter and corresponds to this frequency. The flow rate value is temporarily stored in the uncorrected flow rate value buffer PF secured in the frequency / flow rate calculation work area of the RAM 7, and the process proceeds to the execution of the output processing program.

When the process of output processing is started, the linear correction flag is first referred to, and when this flag designates non-execution of linear correction calculation, the output processing program causes the output flow program to store the measured flow rate stored in the uncorrected flow rate value buffer PF. When the linear correction flag specifies the execution of the linear correction calculation, the linear correction calculation program provided in the output processing program is executed to output the correction value. After that, it returns to the state of waiting for a new sampling time.

When calibrating the actual flow rate of the above Karman vortex flowmeter, the flow rate detecting section 1 is connected to a flow rate standard and tested according to the procedure shown in FIG. First, the setting device 6 of the transmission unit 2
The non-execution of the correction is set in the linear correction flag secured in the EPROM 9 by the so as to start the Karman vortex flowmeter (S
2). With the linear correction flag set as described above so that the measured flow rate data stored in the uncorrected flow rate value buffer PF is displayed and output as is, first, the flow rate of the calibration fluid is set to the full Karman vortex flowmeter to be calibrated. About 25% of scale
A corresponding value is set (S3), and the difference LV1 = PF1-Q1 between the indicated value Q1 of the flow rate reference device and the indicated value PF1 of the Karman vortex flowmeter and the indicated value Q1 of the flow rate reference device at this time is set through the setting device 6 to the EPROM 9 Flow rate calibration point secured in the storage area for flow rate value and flow rate correction amount (LP1) (LV
Write to (1) (S4) (S5).

Subsequently, the flow rate of the calibration fluid is set to about 50%, 75%, and 100% of the full scale of the flowmeter, and the indicated value Qi (i = 2,3,4) and Karman vortex of the flow rate standard are set. The difference between the indication value PFi (i = 2,3,4) of the flow meter and the indication value Qi of the flow rate standard is read and the flow rate value at the flow rate calibration point of the EPROM 9 and the flow rate correction are read through the setter 6. Write to the amount storage area (LP1) (LV1) (S
6) to (S14).

After the above operation is completed, the setting device 6 rewrites the linear correction flag of the EPROM 9 to the correction execution (S2) and ends the calibration test (S16). As a result, the flow rate calibration point flow rate value (LPi) of the EPROM 9
In the storage area of the flow rate correction amount (LV1), the true value of the flow rate is obtained by the line approximation correction from the flow rate value directly measured by the Karman vortex flowmeter. A calibration for drawing a calibration line graph as illustrated in FIG. The data will be stored and held in pairs.

Next, the flow of the arithmetic processing embodiment executed by the linear correction arithmetic program of the output processing program using the calibration data stored in the EPROM 9 is shown in FIG. 5 to explain the correction arithmetic processing. The Karman vortex flowmeter according to the present invention in which the values of the flow rate value (LPi) and the flow rate correction amount (LVi) at each flow rate calibration point obtained by the actual flow calibration test are written in the EPROM 9 is attached to the measurement target flow passage for measurement. When the sampling period elapses, the frequency / flow rate calculation process is executed and the flow rate measurement value is
It is stored in the uncorrected flow rate value buffer PF in the frequency / flow rate calculation work area of AM7, and the processing shifts to output processing.

The output processing program refers to the linear correction flag in the first step (L2). Since this flag is set to the linear correction execution when the actual flow rate calibration test is finished as described above, the following (L4 ) Execute the correction calculation program after the process. Process of correction calculation program (L
In 4), the position of the break point of the polygonal line approximation correction of the following formula (1) is first determined by using the flow rate value (LPi) and the flow rate correction amount (LVi) value at the flow rate calibration point stored in the EPROM 9. The calculation is performed and the correction calculation constant table is temporarily stored in the calculation buffer PFi (i = 1, 2, 3, 4) provided in the linear correction calculation work area of the RAM 7.

[0024]

## EQU1 ## PFi = LPi + LVi (1) However, i = 1, 2, 3, and 4 are successively measured during the current sampling period stored in the uncorrected flow rate buffer PF in the frequency / flow rate calculation work area of the RAM 7. The calculated flow rate value PF is sequentially compared with the break point value stored in the calculation buffer PFi, and the break point position value that is closest to and exceeds the stored value in the uncorrected flow rate value buffer PF is stored. The operation buffer PFi is detected (L5) (L7) (L9), and the operation buffer PFi detected subsequently and the operation buffer PFi-1 corresponding to the break point before the break point corresponding to this calculation buffer are connected to each other. The following formula (2) for obtaining the constant that represents the straight line when approximating the line
Or (6) is performed and the calculated values secured in the linear correction calculation work area of the RAM 7 are temporarily stored in the corresponding calculation buffers (PFS, PFZ, LPS, LPB) (L6) (L8) (L10). (L11).

[0025]

## EQU00002 ## PFS = PFi-PF (i-1) (2)

[0026]

(3) PFZ = PFi (3)

[0027]

## EQU00004 ## LPS = LPi-LP (i-1) (4)

[0028]

## EQU00005 ## LPB = LPi (5) where i = 1, 2, 3, 4 and PF0 = 0 L
P0 = 0 By the above, the value necessary for determining the constant of the equation representing the straight line in the case where the section to which the flow rate value PF measured in the current sampling period belongs is linearly interpolated by the calibration data is obtained. The flow rate true value PFL linearly corrected by the calibration data corresponding to the calculated flow rate value PF is calculated and this value is output (L12) (L13).

[0029]

(Equation 6)

The linearly corrected true value PF of the above flow rate
When the output processing of L is completed, the output processing program returns to the frequency measurement program controlled by the reference period timer interrupt (L14). In the case of the actual flow calibration test in which the linear correction flag is set to non-execution of the linear correction, R
The flow rate measurement value PF stored in the uncorrected flow rate value buffer PF in the AM7 frequency / flow rate calculation work area is the true flow rate value PFL.
(L3) and output as is (L1
3).

[0031]

In the transmission section of the Karman vortex flowmeter according to the present invention, the reference flow rate value at the flow rate calibration point obtained by the reference flowmeter when performing the actual flow rate calibration and the Karman vortex flowmeter to be calibrated. The value of the difference between the directly measured flow rate value and the reference flow rate value is written and stored in the EPROM, and the flow rate true value is obtained by linearly interpolating between the flow rate calibration points according to the stored value in this EPROM. At the time of calibration, it is not necessary to adjust the flow rate of the calibration fluid to be passed through the flow rate detection unit to the flow rate value at the flow rate calibration point, and the effect of improving the efficiency of the calibration work is first obtained. Then, since the linear correction calculation is performed using the reference flow rate value at the flow rate calibration point measured by the reference flow meter, there is no error due to the difference between the reference value and the set value, and an accurate and highly reliable measurement value can be obtained. The effect of being able to be obtained is also obtained.

[Brief description of 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 illustrating a flow rate measuring operation of the flow meter of FIG.

FIG. 3 is a diagram illustrating a procedure of an actual flow rate calibration test.

FIG. 4 is a diagram illustrating a polygonal line approximation correction.

FIG. 5 is a flowchart illustrating details of output processing.

[Explanation of symbols]

 1 Karman vortex flow rate detector 2 Transmitter 3 Microcomputer 4 Reference period timer 5 Pulse interval measurement counter 6 Setter 7 RAM 8 ROM 9 EPROM FRB Frequency / flow rate calculation work area buffer LRB Frequency register FLG Linear correction flag LPi (i = 1 , 2,3,4) Flow rate calibration point Flow rate value area LVi (i = 1,2,3,4) Flow rate correction value area

Claims (1)

[Claims] 1. A Karman vortex flow rate detection unit having a Karman vortex sensor as a flow rate detection end, a micro-computer and peripheral devices for measuring and calculating output pulse signals of the flow rate detection unit and performing output processing. A Karman vortex flowmeter comprising a transmission unit and a linear correction flag indicating switching of execution / non-execution of a linear correction calculation to the flow rate measurement value, and a Karman vortex flowmeter measured by a reference flowmeter in an actual flow rate calibration test. The EPROM for writing and holding the flow rate value and the flow rate correction amount value at the flow rate calibration point and the RAM of the micro computer are provided, and the flow rate value and the flow rate correction amount value are used for the flow rate calibration point. The transmission unit includes a correction calculation work area for temporarily storing the count value and the mantissa value generated in the process of linear correction calculation of the flow rate. If the linear correction flag indicates the linear correction calculation when the calculation process of measuring the output pulse signal of the flowmeter to obtain the flowrate is performed, the output pulse of the flowrate detection unit is obtained by the frequency / flowrate calculation processing. With respect to the measured flow rate, the correction value is calculated by linear interpolation using the flow rate value of the flow rate calibration point and the value of the flow rate correction amount read from the EPROM, and output processing is performed, and the linear correction flag instructs the linear correction calculation. If not, the Karman vortex flowmeter is characterized in that the output pulse of the flow rate detector is subjected to frequency / flow rate calculation processing and the flow rate measurement value obtained is directly output processed.