JP3622613B2 - Ultrasonic flow meter - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an ultrasonic flowmeter.
[0002]
[Prior art]
Conventional ultrasonic flowmeters are generally as shown in FIG. This apparatus includes an ultrasonic transducer 2 installed in a measurement flow path 1 through which a fluid flows, a drive circuit 3 that drives the ultrasonic transducer 2, a control unit 4 that outputs a start signal to the drive circuit 3, an ultrasonic wave A propagation time measuring unit 5 that measures the propagation time, a calculation unit 6 that receives measurement data from the propagation time measuring unit 5, an ultrasonic transducer 7 that receives ultrasonic waves transmitted from the ultrasonic transducer 2, and an ultrasonic transducer 7 and the reception detection circuit 9 that compares the output of the amplifier 8 with the reference voltage and stops the propagation time measurement unit 5 when the magnitude relationship is inverted.
[0003]
In the ultrasonic flowmeter, the drive circuit 3 that has received the start signal from the control unit 4 performs pulse driving of the ultrasonic transducer 2 for a certain period of time, and at the same time, the propagation time measurement unit 5 receives time from the signal from the control unit 4. Start measuring. Ultrasound is transmitted from the pulse-driven ultrasonic transducer 2. The ultrasonic wave transmitted from the ultrasonic transducer 2 propagates through the fluid to be measured and is received by the ultrasonic transducer 7. The reception output of the ultrasonic transducer 7 is amplified by the amplification factor set by the control unit 4 in the amplifier 8. Then, the reception detection circuit 9 receiving the output of the amplifier 8 determines reception of the ultrasonic wave and stops the propagation time measuring unit 5. Then, the control unit 4 obtains the flow velocity from the time information t obtained from the propagation time measuring unit 5 by (Equation 1) (however, the measurement time obtained from the propagation time measuring unit 5 is t and the flow direction between the ultrasonic transducers is determined. The effective distance is L, the speed of sound c, and the flow velocity of the fluid to be measured is v).
[0004]
v = (L / t) -c (Formula 1)
The received signal has a waveform that rises gently, and the level of the received signal changes depending on the temperature characteristics of the ultrasonic transducer and the flow velocity. If the relationship between the reference voltage and the level of the received signal is not appropriate, the operation of the reception detection circuit 9 is not stable and the measurement accuracy is deteriorated.
[0005]
As another measurement method, the determination result of the reception detection circuit 9 may be returned to the drive circuit 3 by the feedback circuit instead of the propagation time measurement unit 5 and transmitted again. There was also a method of performing such a repetitive operation a predetermined number of times, measuring the time, and obtaining the flow velocity by calculation of (Equation 2) based on the measurement time (provided that the number of repetitions is n, the measurement time is ts, The effective distance in the flow direction between the ultrasonic transducers is L, the sound velocity is c, and the flow velocity of the fluid to be measured is v).
[0006]
v = L / (ts / n) -c (Formula 2)
According to this method, it is possible to measure with a higher n-fold resolution than the method of (Equation 1).
[0007]
There is also a method of switching the ultrasonic transducer 2 and the ultrasonic transducer 7 and measuring the respective propagation times from upstream to downstream and downstream to upstream of the fluid to be measured, and obtaining the velocity v from (Equation 3). (However, the propagation time from upstream to downstream is t1, and the propagation time from downstream to upstream is t2.)
[0008]
v = L / 2 ((1 / t1)-(1 / t2)) (Formula 3)
According to this method, the flow velocity can be measured without being affected by the change in the sound speed, and thus it is widely used for measuring the flow velocity, the flow rate, the distance, and the like.
[0009]
[Problems to be solved by the invention]
However, with conventional ultrasonic flowmeters, the timing of reception detection is shifted due to changes in waveform and amplitude due to flow fluctuations, noise, etc., and accurate flow measurement cannot be performed or the measured flow volume increases, Disturbances such as vortices occur in the propagation path of the sound wave, the received signal fluctuates greatly in a short time, the reception timing is shifted, and erroneous measurement may occur, but it cannot be determined as erroneous measurement.
[0010]
An object of the present invention is to discriminate between the above-described erroneous measurement and normal measurement, and to prevent a decrease in measurement accuracy due to the erroneous measurement.
[0011]
[Means for Solving the Problems]
In order to solve the above problems, the present invention compares the propagation time of the ultrasonic wave obtained for measuring the flow velocity of the fluid to be measured with the propagation time during normal measurement, and determines whether or not the flow measurement has been performed normally. By providing the measurement determination means, it is possible to prevent a decrease in measurement accuracy due to erroneous measurement.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
The ultrasonic flowmeter according to the first means of the present invention includes a pair of ultrasonic transducers capable of transmitting and receiving ultrasonic signals, and an ultrasonic signal transmitted from one of the ultrasonic transducers and propagating a fluid. A propagation time measurement unit that measures the propagation time of the ultrasonic wave until the ultrasonic transducer receives, a calculation unit that obtains the flow rate of the fluid that fills between the ultrasonic transducers by calculation from the propagation time, and a flow during flow measurement The propagation time in the direction and the propagation time in the reverse flow direction, and the propagation time in the flow direction and the propagation time in the reverse flow direction when it can be measured normally are stored, and the propagation time is stored each time the measurement is normally completed. The propagation time storage means to be updated, the absolute value of the change in the flow direction propagation time during flow rate measurement and the flow direction propagation time stored in the propagation time storage means, and the reverse flow direction propagation time during flow measurement And recorded in the propagation time storage means By comparing the absolute value of the propagation time and the amount of change in the reverse flow direction, by providing an erroneous measurement determining means for determining an erroneous measurement when there is a difference greater than a predetermined magnitude between the amount of change, not It is possible to prevent measurement accuracy from deteriorating due to erroneous measurement due to regular flow fluctuations or electrical noise. In addition, it becomes possible to discriminate erroneous measurement due to irregular flow rate fluctuations and electrical noise rather than fluctuations in propagation time.
[0013]
【Example】
Embodiments of the present invention will be described below with reference to the drawings.
[0014]
Example 1
FIG. 1 is a block diagram showing an ultrasonic flowmeter according to the first means of the present invention. The basic configuration is the same as in the description of the conventional example. The difference between the present example and the conventional example is that the ultrasonic transducers 2 and 7 can transmit and receive, and the changeover switch 10 is provided so that the flow direction and the reverse flow are reversed. That is, the propagation time in the direction can be measured and the erroneous measurement determination means 11 is provided. The operation of the erroneous measurement determination unit will be described with reference to FIG. First, the average value h of the propagation times t1 and t2 in the flow direction and the reverse flow direction measured by the propagation time measurement unit 5 is obtained, and the difference between the preset average value H of the propagation times T1 and T2 during normal measurement is obtained. . Although the propagation time varies depending on the flow size, the average value in the flow velocity direction and the reverse flow direction is constant regardless of the flow size. Therefore, if the average value changes significantly, it is considered that there is some abnormality in the measurement system. Therefore, if the difference between the average values is larger than the predetermined value A, it can be determined that the measurement is incorrect. Here, A is a value that takes into account fluctuations due to environmental changes during propagation time measurement.
[0015]
(Example 2)
FIG. 3 is a block diagram showing an ultrasonic flowmeter according to the second means of the present invention. The basic configuration is the same as that of the first embodiment of the present invention, and the difference between the present embodiment and the first embodiment is that a propagation time storage means 12 is provided. The propagation time storage means 12 is set in consideration of changes in the propagation time due to changes in the surrounding environment, etc., because the normal propagation time used for judgment by the erroneous measurement judgment means 11 is updated every time measurement ends normally. Since the predetermined value A can be made smaller than that of the first embodiment, erroneous measurement can be determined with higher accuracy.
[0016]
(Example 3)
FIG. 4 shows the erroneous measurement determination means 11 of the ultrasonic flowmeter according to the third means of the present invention. The difference between the present embodiment and the first embodiment is that the fluctuation values in the flow direction and the reverse flow direction are used for determination of erroneous measurement without using the average value of the propagation time. When the flow rate changes, the propagation time changes ts1 and ts2 in the flow direction and the reverse flow direction have the same sign but opposite in magnitude, and when the temperature of the measurement fluid changes, the flow direction and the reverse flow direction Since the propagation time changes ts1 and ts2 are the same, if the difference between the absolute values of the propagation time changes in the flow direction and the reverse flow direction is greater than or equal to the predetermined magnitude A, it can be regarded as an erroneous measurement.
[0017]
As described above, according to each embodiment of the present invention, the following effects can be obtained.
[0018]
Compared to conventional ultrasonic flowmeters, it can be determined that flow measurement has not been completed normally due to irregular flow fluctuations or electrical noise, so that it is possible to prevent measurement accuracy from being lowered due to erroneous measurement.
[0019]
In addition, by updating the normal propagation time, it is not necessary to set a large predetermined size A as a determination reference in consideration of fluctuations in the propagation time due to environmental changes, so the determination accuracy of erroneous measurement can be further improved. .
[0020]
Furthermore, even if the sound speed itself changes due to a change in the ambient temperature of the ultrasonic flowmeter, it is not erroneously determined as an erroneous measurement, and a decrease in measurement accuracy can be further prevented.
[0021]
【The invention's effect】
As described above, according to the ultrasonic flowmeter according to the first means of the present invention, the flow measurement cannot be normally terminated due to irregular flow fluctuations or electrical noise as compared with the conventional ultrasonic flowmeter. Therefore, it is possible to prevent the measurement accuracy from being lowered due to erroneous measurement. Further, even when the sound speed itself changes due to the change in the ambient temperature of the ultrasonic flowmeter, it is not erroneously determined to be an erroneous measurement, and it is possible to further prevent a decrease in measurement accuracy.
[Brief description of the drawings]
FIG. 1 is a configuration diagram of an ultrasonic flowmeter in Embodiment 1 of the present invention. FIG. 2 is a diagram showing a procedure for determining erroneous measurement of the same flow. FIG. 3 is a configuration of an ultrasonic flowmeter in Embodiment 2 of the present invention. FIG. 4 is a diagram showing an erroneous measurement determination procedure of an ultrasonic flow meter in Embodiment 3 of the present invention. FIG. 5 is a configuration diagram of a conventional ultrasonic flow meter.
DESCRIPTION OF SYMBOLS 1 Measurement flow path 2 Ultrasonic vibrator 3 Drive circuit 4 Control part 5 Propagation time measurement part 6 Calculation part 7 Ultrasonic vibrator 8 Amplifier 9 Reception detection circuit 10 Changeover switch 11 Incorrect measurement determination means 12 Propagation time memory means

Claims (1)

A pair of ultrasonic transducers capable of transmitting and receiving ultrasonic signals, and an ultrasonic propagation time until the other ultrasonic transducer receives an ultrasonic signal transmitted from one ultrasonic transducer and propagating through a fluid. A propagation time measurement unit for measuring, a calculation unit for obtaining a flow rate of the fluid that fills between the ultrasonic transducers by calculation from the propagation time, a propagation time in the flow direction and a propagation time in the reverse flow direction during flow measurement , Propagation time storage means for storing the propagation time in the flow direction and the propagation time in the reverse flow direction when the measurement can be normally performed, and updating the propagation time every time measurement is normally completed, and the flow direction during flow measurement The absolute value of the amount of change between the propagation time in the flow direction and the propagation time in the flow direction stored in the propagation time storage means, the propagation time in the reverse flow direction during flow rate measurement, and the propagation in the reverse flow direction stored in the propagation time storage means Absolute amount of change with time Comparing the values, ultrasonic flowmeter having the erroneous measurement determining means for determining an erroneous measurement when there is a difference greater than a predetermined magnitude between the amount of change.

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