JP4425415B2 - Flow measuring device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a flow rate measuring device that measures the flow rate of a fluid such as a gas.
[0002]
[Prior art]
A conventional flow measuring device of this type will be described with reference to FIGS. This flow rate measuring device includes an instantaneous or analog flow detection means 2 for detecting a fluid flow state in a part of a flow path 1, and an output signal of the flow detection means 2 is amplified or digitized by a signal processing means 3. ing.
[0003]
When there is a periodic fluctuation in the fluid flow state, the fluid flow rate measurement value varies depending on the timing of measurement by the flow detection means 2. For example, in a gas meter that measures household gas consumption, pressure fluctuation occurs when a gas engine is operated nearby. When the flow rate fluctuates as a result, the signal is averaged by the averaging means 4 and the average flow rate is calculated by the flow rate calculation means 5. FIG. 6 is a diagram showing the flow rate waveform at this time, and the flow rate indicated by the line A actually flows.
[0004]
Since the instantaneous measurement device measures the flow rate intermittently, values such as flow rate Q1 (time t1), flow rate Q2 (time t2), flow rate Q3 (time t3) are obtained, and the flow rate is calculated by the microcomputer. It was. In the case of an analog type, continuous signals from time t0 to t4 are averaged through an integrator.
[0005]
In addition, using a pressure sensor or the like, the flow measurement is started or stopped in synchronization with the pressure of the fluid, and as shown in FIG. 7, between the time t1 and t2, that is, one cycle of the pressure fluctuation waveform (a cycle of an integral multiple of that). In some cases, the average flow rate was calculated by measuring the flow state.
[0006]
[Problems to be solved by the invention]
However, in order to measure the accurate flow rate at the time of pressure fluctuation in the conventional flow rate measuring device, since the digital type intermittently samples, it is necessary to increase the number of times of measurement and average the measured value, so that the measurement time is In the case of an analog type, it has to be continuously measured, and there is a problem that power consumption increases in any case.
[0007]
In addition, in the case where the flow rate measurement is started or stopped using the pressure sensor, the timing may not be accurately obtained, and an error may occur in the measured flow rate value. That is, in FIG. 7, when the measurement is stopped at time t2 ′ without being accurately synchronized with the pressure, an error occurs in the average flow rate because it deviates from one cycle. In particular, in the vicinity of time t2, the rate of change of pressure is large, so the flow rate that changes is large, and even a small time error causes a large flow rate error. Although the accuracy can be improved by increasing the number of measurements in order to eliminate this error, the power consumption increases accordingly.
[0008]
Accordingly, the present invention solves the above-described problems, and in a flow rate measuring device that is used for a long time with a battery such as a gas meter, the flow rate measurement can accurately measure the flow rate of the fluid at the time of pressure fluctuation with low power consumption. An object is to provide an apparatus.
[0009]
[Means for Solving the Problems]
In order to achieve the above object, the present invention provides a flow rate measuring means for measuring a flow rate based on a signal of a flow detecting means for detecting a flow state of a fluid in a flow path, a pressure detecting means for detecting a pressure of the fluid, Measurement start / stop means for outputting a measurement start signal for starting the flow rate measurement of the flow rate measurement means and a measurement stop signal for stopping the flow rate measurement, and a variation measurement control means for controlling the flow rate measurement means via the measurement start / stop means The fluctuation measurement control means includes a pressure fluctuation value detected by the pressure detection means, a preset L level pressure set value, and an H level pressure set value higher than the L level pressure set value. comparing, as the vicinity of the peak value of the pressure variation value falls in the middle of the H-level pressure set value and the L level pressure setting value, and the variable gain amplifying means for varying the amplification degree of the pressure variation value When the pressure fluctuation value output from the variable gain amplifying means exceeds the L level pressure set value, the signal is output to the measurement start / stop means to output a measurement start signal from the measurement start / stop means. Comparing means for outputting a signal to the measurement start / stop means and outputting a measurement stop signal from the measurement start / stop means when the fluctuation value exceeds the L level pressure set value is provided. is there.
[0010]
According to the present invention, the variable gain amplifying means of the fluctuation measurement control means amplifies the AC component of the pressure fluctuation value of the pressure detection means so that it can be compared with the comparison set value, and the amplified pressure fluctuation value is compared with the comparison means. The flow rate measurement of the flow rate measuring means is started or stopped via the measurement start / stop means at the timing when the magnitude has changed to a predetermined level. Therefore, even when the pressure changes, the pressure waveform is automatically corrected to an appropriate level, and flow measurement can be started or stopped near the peak value of the pressure waveform, that is, at a portion where the changing flow rate is small. Even if a time error occurs, the average flow rate can be maintained with high accuracy. And since there is no need to increase the number of measurements and averaging, the power consumption can be reduced, and the flow rate can be accurately measured with low power consumption even during pressure fluctuations with a flow meter such as a gas meter that can be used for a long time with batteries. Can do.
[0011]
Moreover, since the vicinity of the peak value of the pressure variation waveform so as to control the variable gain amplifying means so as to be positioned between the L-level pressure setpoint and H-level pressure setting, the flow rate error hardly occurs pressure waveform in the vicinity of the peak value can be automatically corrected to allow flow measurement, Ru can be specifically carried out the action with a simple structure in.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
[0013]
FIG. 1 is a block diagram showing a flow rate measuring apparatus according to a first embodiment of the present invention. In this flow rate measuring device, a first transmitter / receiver 8A that transmits or receives ultrasonic waves and a second transmitter / receiver 8B that receives or transmits ultrasonic waves are arranged in the flow direction in the middle of the flow path 7 and are switched by the switching means 16. Transmission and reception can be switched, and the flow state of fluid such as gas is detected. Reference numeral 9 denotes a flow rate measuring means for processing the signal of the flow detection means 8 to measure the flow rate. Reference numeral 10 denotes a transmission means. The trigger means 11 drives the first transmitter / receiver 8A toward the second transmitter / receiver 8B, that is, upstream. Ultrasonic waves are transmitted downstream. The amplifying means 12 amplifies the signal received by the second transmitter / receiver 8B, the amplified signal is compared with the reference signal by the comparing means 13, and after the signal equal to or higher than the reference signal is detected, the repeating means 14 triggers again. Transmission is performed from the means 11, and the above transmission / reception is repeated a predetermined number of times, and each time value is measured by the time measuring means 15 such as a timer counter.
[0014]
Next, the switching means 16 switches between transmission / reception of the first transmitter / receiver 8A and the second transmitter / receiver 8B, and transmits an ultrasonic signal from the second transmitter / receiver 8B to the first transmitter / receiver 8A, that is, from downstream to upstream. Is repeated as described above, and each time value is measured. Then, the flow rate value is obtained by the signal processing means 17 in consideration of the size of the flow path 7 and the flow state of the fluid from the difference in propagation time of the ultrasonic waves between the first transceiver 8A and the second transceiver 8B. The flow path 7 is provided with pressure detection means 18 for detecting flow rate fluctuations by pressure. The pressure signal detected by the pressure detection means 18 is processed by the fluctuation measurement control means 19, and based on the signal of the fluctuation measurement control means 19. Then, the measurement of the flow rate measuring means 9 is started or stopped via the measurement start / stop means 20. The fluctuation measurement control means 19 includes a variable gain amplification means 19A for amplifying the signal of the pressure detection means 18 and a comparison means 19B for comparing the signal of the variable gain amplification means 19A with a preset reference value (comparison set value). Then, a signal is sent to the measurement start / stop means 20. The variable gain amplification means 19A can change the amplification degree by setting. Reference numeral 21 denotes a measurement control means having a timer means 21A therein, and sends a measurement request command to the measurement start / stop means 20 at a timing designated by the microcomputer.
[0015]
Next, the operation will be described. When the flow state of the fluid in the flow path 7 is relatively gentle and the value of the pressure detecting means 18 does not vary, normal flow rate measurement is performed. That is, when the switching means 16 is set to transmit ultrasonic waves from the first transmitter / receiver 8A to the second transmitter / receiver 8B, and the first measurement start signal is transmitted from the measurement start / stop means 20, the time measuring means is transmitted. At the same time as resetting 15, an ultrasonic signal is transmitted from the first transmitter / receiver 8 </ b> A via the transmitting means 10. When the propagation of the ultrasonic signal is detected by the amplification means 12 and the comparison means 13 after being received by the second transmitter / receiver 8B, the signal is sent again to the trigger means 11 by the repeat means 14 and the second ultrasonic wave is transmitted. To do. The repeat means 14 is set with a repeat count, and at the same time as the predetermined repeat count is reached, the time measuring means 15 measures the time between the first transceiver 8A and the second transceiver 8B to calculate the flow rate.
[0016]
When the fluid in the flow path 7 fluctuates, the pressure detection means 18 detects the flow fluctuation by pressure, sends a signal to the fluctuation measurement control means 19, and flows through the measurement start / stop means 20 according to the timing of the change in magnitude. The measuring means 9 is controlled. Sampling for flow rate measurement is performed once every few seconds, and if there is a periodic fluctuation in the flow in the flow path 7, the flow rate measurement value fluctuates and can be determined. The measurement control means 21 has a timer means 21A. When a predetermined time is reached, the fluctuation measurement control means 19 is activated to capture the fluctuation signal value. This signal is amplified by the variable gain amplifying means 19A and is compared by the comparing means 19B. When a signal of a predetermined level or higher is detected, the measurement start / stop means 20 starts measuring the flow rate measuring means 9.
[0017]
When the measurement is started in synchronization with the pressure waveform, the error is smaller in the measured flow rate value when the measurement is started or stopped near the peak value of the pressure waveform. This is because the flow rate waveform is 90 degrees out of phase with the pressure waveform, and the vicinity of the peak value is the central value of the flow rate (close to the average value), and the pressure fluctuation is small and the fluctuation flow rate is also small. That is, even if the timing for starting or stopping the measurement shifts and an error occurs in time, the error can be reduced where the flow rate fluctuates is small.
[0018]
FIG. 2 is a diagram showing the output of the measurement control means 21, the fluid pressure fluctuation waveform, the output of the comparison means 19B, and the output of the measurement start / stop means 20. The output of the comparison means 19B is turned on when the pressure fluctuation waveform is larger than the pressure fluctuation value compared with the comparison set value, and turned off when the pressure fluctuation waveform is smaller than that. Since the pressure fluctuation waveform A has a small level and does not reach the comparison set value, a signal for starting measurement cannot be obtained. The pressure fluctuation waveform B is a waveform obtained when the amplification factor of the variable gain amplifying means 19A is increased for the signal of the pressure fluctuation waveform A. The pressure fluctuation waveform B becomes equal to or higher than the comparison set value near the peak value, and can be detected.
[0019]
At time t1, a measurement request signal is sent from the measurement control means 21, but since the signal of the comparison means 19B of the fluctuation measurement control means 19 is OFF, it is in a state of waiting for measurement, and at time t2, the signal of the pressure detection means 18 is When the output of the comparison means 19B is changed to ON, a signal is sent to the measurement start / stop means 20, and the flow rate measurement means 9 starts the flow rate measurement means 9 from the trigger means 11. Then, a signal is sent to the measurement start / stop means 20 at time t3 when the comparison means output is turned off and turned on again. When this signal repeatedly passes the signal to the means 14, the measurement of the flow rate measuring means 9 is stopped, and the time propagation means 15 calculates the ultrasonic propagation time. In this way, measurement is started near the peak value of the pressure fluctuation waveform, and measurement is ended near the peak value after measurement for one period. Further, the switching means 16 is switched and the transmission direction is reversed, and measurement is performed in the same manner as described above. In this embodiment, the pressure fluctuation waveform is similar to a sine wave, but the same effect can be obtained with other waveforms.
[0020]
The fluctuation measurement control means 19 of the second embodiment of the present invention is shown in FIG. The comparison means of the fluctuation measurement control means 19 includes an L level comparison means 19C and an H level comparison means 19D. As shown in FIG. 4, the L level comparison means 19C has a low comparison set value, and the H level comparison means 19D has a high comparison set value. The variable gain amplifying means 19A can vary the degree of amplification, and the variable gain amplifying means 19A is automatically set so that the L level comparing means 19C is higher than the L comparison set value and the H level comparing means 19D is lower than the H comparison set value. Change the degree of amplification. As shown in the time chart of FIG. 4, the variable gain amplification means 19A amplifies the amplified pressure signal so that the peak value of the amplified pressure signal is between the L level comparison set value and the H level comparison set value. Transmission to the measurement start / stop means 20 is performed at times t3 and t5 which are rising signals of the L level comparison means 19C. As a result, the measurement is started and stopped near the peak value of the fluctuation waveform.
[0021]
【The invention's effect】
As is clear from the above description, according to the flow rate measuring device of the present invention, even if the pressure level changes, the fluctuation value is automatically corrected to a size that can be used to start or stop the measurement, Measurement can be performed in synchronization with the pressure fluctuation waveform accurately, and even if the timing is shifted, the flow rate error can be reduced and the average flow rate can be measured accurately. In addition, since there is no need to increase the number of measurements and averaging, the power consumption is reduced, and the flow rate is accurately measured with low power consumption even when the pressure fluctuates with a flow meter such as a gas meter that is used for a long time with batteries. Can do.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a flow rate measuring device according to a first embodiment of the present invention.
FIG. 2 is a time chart showing flow rate measurement when the flow rate is changed in the embodiment.
FIG. 3 is a block diagram showing a main part (variation detection control means) of a flow rate measuring device according to a second embodiment of the present invention.
FIG. 4 is a time chart showing flow rate measurement when the flow rate is changed in the embodiment.
FIG. 5 is a block diagram showing a conventional flow rate measuring apparatus.
FIG. 6 is a time chart showing flow rate measurement when the flow rate is changed in a conventional example.
FIG. 7 is a time chart showing flow rate measurement at the time of flow rate fluctuation in another conventional example.
[Explanation of symbols]
8 Flow detection means 9 Flow measurement means 18 Pressure detection means 19 Fluctuation measurement control means 19A Variable gain amplification means 19B Comparison means 19C L level comparison means 19D H level comparison means 20 Measurement start / stop means

Claims (1)

A flow rate measuring means for measuring a flow rate based on the signal flow detecting means for detecting the fluid flow conditions in the flow path, a pressure detecting means for detecting the pressure of the fluid, the measurement starting the flow measurement of the flow rate measuring means A measurement start / stop means for outputting a start signal and a measurement stop signal for stopping the flow rate measurement, and a fluctuation measurement control means for controlling the flow rate measurement means via the measurement start / stop means, the fluctuation measurement control means, a pressure fluctuation value detected by the pressure detecting means is compared with the H-level pressure setpoint of preset L level pressure setpoint and higher than the L level pressure setpoint, the peak value of the pressure variation value near to enter the middle between the H level pressure set value and the L level pressure setting value, and the variable gain amplifying means for varying the amplification degree of the pressure variation value, is output from the variable gain amplifying means When the measured pressure fluctuation value exceeds the L level pressure set value, the signal is output to the measurement start / stop means and a measurement start signal is output from the measurement start / stop means, and then the pressure fluctuation value becomes the L level pressure set value. A flow rate measuring apparatus comprising: a comparison unit that outputs a signal to the measurement start / stop unit and outputs a measurement stop signal from the measurement start / stop unit.

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