JPS6050287B2 - Ultrasonic measuring device - Google Patents

Description

Detailed Description of the Invention This invention measures the flow rate, level, etc. by detecting the time until the ultrasonic pulse is delivered after transmitting an ultrasonic pulse, etc. using an ultrasonic flowmeter, an ultrasonic level meter, etc. The present invention relates to an ultrasonic measuring device.

Ultrasonic flowmeters require highly accurate detection to detect the point in time when a particular wave of an ultrasonic carrier wave is received in a received ultrasonic pulse.

Misdetection of that particular wave will result in large measurement errors. For example, the received pulse may become instantaneously larger or smaller due to the presence of bubbles or dirt contained in the fluid being measured. detection, which results in a measurement error of one wave number or more. The present invention is designed to eliminate such measurement errors.

First, we will specifically point out the problems with conventional ultrasonic flowmeters and then explain the present invention. As shown in Fig. 1, the ultrasonic flowmeter has a pair of ultrasonic transducers 12 and 13 installed diagonally opposite to each other with respect to the axis of the pipe in a pipe 11 having an inner diameter of D. There is.

The distance between the transducers 12 and 13 is 1, and the transducer 1
The angle between the line connecting 2 and 13 and the conduit 11 is O, the conduit 11
When the flow velocity of the fluid to be measured flowing through the tube is V1 and the sound speed of the ultrasonic wave in the fluid is c, the time T1 required for the ultrasonic pulse transmitted from the transducer 12 to be received by the transducer 13 is The arrival time T of the ultrasonic pulse between the transducers 12 and 13 when the wave is transmitted along the flow of the fluid flowing in the path 11 is as follows.

On the other hand, the time required for the wave to be transmitted from the transducer 13 and received by the transducer 12 is as follows.

Since l is -y-, the relationship between equations (1) and (2) is
The following equation (3) is derived from the COSO section.

Since D and 0 are constant, the time it takes for the ultrasonic pulse to propagate between the transducers 12 and 13 is measured in the direction along and against the flow of the fluid to be measured, and the difference in the reciprocals of each is found. The flow velocity of the fluid to be measured can be obtained.

Incidentally, the received ultrasonic pulse generally has a carrier wave envelope that gradually rises and then gradually falls, as shown in FIG. 2A. A comparator detects the part of the wave larger than the reference level L1, which is a certain level above the 0 level, to obtain a square wave output as shown in FIG. The pulse of the second wave from the rise of the ultrasonic pulse is used for measurement.

However, when the amplitude of the received ultrasonic pulse decreases and becomes as shown in Figure 2C, the portion exceeding the reference level L1 is shown in Figure 2D.
As shown in the figure, it becomes the third wave. This third wave is detected as the second wave from its rise, that is, as a normal wave, and this is used as the arrival point of the received pulse, and an error E of one cycle of the carrier wave is eliminated in measuring the arrival time of the ultrasonic pulse. occurs. Ultrasonic flowmeters generally need to measure the transmission time of ultrasonic pulses with high accuracy of several nanoseconds.

However, when the carrier frequency of the ultrasonic pulse is 1 MHz, if an error E for one cycle occurs as shown in FIG. 2, this will be about 1 microsecond. This error reaches the required accuracy of 20@, making it impossible to perform correct measurements. Conventionally, in order to reduce the influence of changes in the amplitude of received ultrasonic pulses, automatic gain control has been used to keep the amplitude of received ultrasonic pulses constant.

Furthermore, when a received ultrasonic pulse cannot be obtained, that is, when a received pulse disappears momentarily, the measurement results up to that point are held to prevent the measured value from changing significantly. However, when controlling the received ultrasonic pulse to a constant amplitude using automatic gain control, each time an ultrasonic pulse is received, the set value is compared with the amplitude of the received ultrasonic pulse, and the gain of the variable gain amplifier is controlled depending on the magnitude. I will do it. Therefore, received pulses with a constant amplitude can be obtained on average. However, the amplitude of the received pulse actually received cannot be set to a constant value. In other words, after receiving ultrasonic pulses, the gain is controlled by comparing them, and if the next received pulse has the same amplitude as the previous pulse, it is kept constant, and the received pulse before this control is A constant pulse is not possible. The amplitude of the first received pulse whose amplitude has changed cannot be kept constant. In reality, the amplitude of the received pulse fluctuates considerably because bubbles and foreign matter are mixed into the fluid to be measured. It has been impossible to prevent errors based on this variation by automatic gain control. Also, as mentioned earlier, if the received ultrasonic pulse is not detected, even if the measured value up to that point is retained, if the amplitude of the received ultrasonic pulse becomes large, the wave one or more earlier than the normal wave will be detected. It is detected as a normal wave, and therefore no error prevention action is taken against such an error. Also, if the received wave does not disappear but is slightly attenuated and the normal wave drops slightly below the reference level, the next wave or the wave after that will be detected as a normal wave, and as shown in Figure 2. This produces the error E as described above. The purpose of this invention is to accurately measure the propagation time by detecting a predetermined regular wave of the carrier wave of the received ultrasonic pulse without fail, even if the amplitude of the received ultrasonic pulse changes instantaneously, as long as it is above a reference level. However, it is an object of the present invention to provide an ultrasonic measuring device that can hold the measurement data of the propagation time up to now if it is below the reference level. In general, the measured value does not fluctuate rapidly, so the time of reception of the ultrasonic pulse does not change suddenly, and the change in the measured value is generally quite slow relative to the repetition rate at which repeated measurements are taken. The reception time of the next received pulse can be predicted from the measurement time up to that point.

In the present invention, normal waves are detected from the received pulses only in a narrow range before and after this predicted time point. In this way, it is possible to prevent errors caused by amplitude fluctuations.
That is, a variable delay circuit is driven in synchronization with the transmission of an ultrasonic pulse, and from the delayed output of the variable delay circuit, a pulse having a constant time width corresponding to approximately one cycle of the carrier wave of the ultrasonic pulse is generated by a pulse generation circuit. let

On the other hand, when the received ultrasonic pulse exceeds the first reference level, the comparator generates an output, and the time difference detection circuit extracts the time difference between the output of the comparator and the output pulse from the previous pulse generation circuit. An output corresponding to the time difference is supplied to a time constant circuit to average out fluctuations, and the amount of delay of the variable delay circuit is controlled by the output of the time constant circuit. As a result, the pulse of the pulse generating circuit temporally follows the output of the comparator. As mentioned earlier, the output pulse of the pulse generation circuit is a narrow pulse of approximately one period of the carrier wave, and in a steady state, it is compared only with the part corresponding to the normal wave in the next received pulse. In other words, the pulse follows the regular wave. Therefore, a reception detection pulse is extracted using a gate circuit based on the pulse of the pulse generation circuit, and the output pulse of this gate circuit is used as a regular reception detection pulse to measure the time from transmission to reception of the ultrasonic pulse. Correct time measurements can be made in this way. Even if the amplitude of the received pulse changes instantaneously, it is averaged by the time constant circuit, so it is not affected by such instantaneous fluctuations.

However, when the reception time gradually changes, the pulse generation time of the pulse generation circuit changes in accordance with the reception time. The time difference detection described above is used to advance the phase of the pulse from the pulse generation circuit by a fixed value so that the center of the pulse width coincides with the reference point of the regular wave, for example, the point where it passes the O level. A constant value can be added to the output of the circuit and supplied to the time constant circuit. Furthermore, when the amplitude of the received pulse fluctuates significantly, there is a possibility that the previous wave will be erroneously received compared to the normal wave because the number of waves existing before it is small to begin with. It is more likely that the rear wave will be mistakenly detected as a regular wave.

From this point of view, the conversion gain of the time difference detection circuit should be set so that the conversion gain when the comparator output is ahead of the pulse of the pulse generation circuit is larger than the conversion gain when the comparator output lags behind the pulse of the pulse generation circuit. It is preferable. Next, an example in which the ultrasonic measuring device according to the present invention is applied to an ultrasonic flow meter will be explained with reference to FIG.

The ultrasonic pulse generation circuit 16 is driven by the rising edge of the clock pulse from the input terminal 15. The ultrasonic pulses from the ultrasonic pulse generation circuit 16 are excited by the transducer 12, and the ultrasonic pulses from this propagate within the fluid to be measured in the conduit 11 and reach the transducer 13. The ultrasonic pulse received by the transducer 13 is received and amplified in the receiving circuit 17, and its output is compared with a first reference level in the comparator 18. For example, as shown in FIG. 4A, the received pulse of the output of the receiving circuit 17 is compared with the first reference level L1 in the comparator 18, and when it exceeds L1, it rises and reaches the second reference level (for example, zero level). An output falling at 0 is obtained as shown in FIG. 4B.

A pulse (FIG. 4C) that rises at the falling edge of the output of the comparator 18 is generated by a reception detection pulse generating circuit 19 as a reception detection pulse. On the other hand, the variable delay circuit 21 is driven by the rising edge of the clock from the terminal 15.

The delay amount of the variable delay J circuit 21 is controlled by a control signal, and the pulse generation circuit 22 is driven by the delay output of the variable delay circuit 21. In the present invention, the pulse width of this pulse generating circuit is set to a time width i corresponding to approximately one cycle of the carrier wave of the ultrasonic pulse.

The time difference between this pulse and the leading edge (rising edge) of the output from the comparator 18 is detected by the time difference detection circuit 23. A voltage proportional to the time difference between the leading edge of the output of the comparator 18 and the rise of the output pulse of the pulse generation circuit 22 is obtained from the time difference detection circuit 23, and this output voltage is integrated in the time constant circuit 24. The signal is supplied to the variable delay circuit 21 as a control signal for controlling the amount of delay. By this control, the rising edge of the output of the comparator 18 and the rising edge of the output pulse of the pulse generating circuit are made to coincide. In other words, in FIG. 4, the pulse shown in FIG. 4D, which coincides with the rising edge of the pulse in FIG. The variable delay circuit 21 is controlled so as to be obtained from the signal 22. The gate circuit 25 is opened by the output pulse of this pulse generation circuit 22, and the detection pulse generation circuit 1 receives this gate circuit 25.
9, that is, the reception detection pulse shown in FIG. 4C passes through and is supplied to the output terminal 26.

In other words, although not shown in the figure, a normal reception detection pulse is supplied through the terminal 26 to a measuring circuit similar to a conventional time difference measuring circuit.

The time from the transmission of the ultrasonic pulse to this regular reception detection pulse is measured. In this example, by such measurements, the times T and T of the equations (1) and (2) are measured,
Furthermore, the flow velocity V1 is calculated from equation (3), and the flow rate is calculated using this. In such a configuration, in the initial state, the delay amount of the variable delay circuit 21 is 0, and therefore the pulse of the pulse generation circuit 22 gradually advances with respect to the leading edge of the output of the comparator 18, so that the variable delay Control is performed to increase the delay amount of the circuit 21, and the pulse of the pulse generating circuit 22 gradually comes to coincide with the leading edge of the output of the comparator 18.

When these match, the amplitude of the received pulse changes abnormally due to air bubbles, foreign matter, etc., and the output of the comparator 18 momentarily shifts by one wavelength of the ultrasonic carrier wave, moves forward, lags behind, or shifts several times. Changes by wavelength, hours. Even if the detected value of the difference detection circuit 23 suddenly changes from the previous value, it is averaged by the time constant circuit 24, and the delay amount of the variable delay circuit 21 is not controlled to a large extent. Therefore, if the next received pulse with a normal amplitude is received, and the pulse amplitude does not vary greatly, the time difference between the leading edge of the output of the comparator 18 obtained from the normal wave and the pulse of the pulse generation circuit 22 Detection is performed. However, if the flow rate of the fluid to be measured in the pipe line 11 changes, the leading edge of the output of the comparator 18 will also gradually move back and forth accordingly.
Since a time difference occurs between the two pulses and this always occurs, the variable delay circuit 21 is controlled and the comparator 1
The pulse of the pulse generating circuit 22 follows the leading edge of the output of the pulse generator 8.

Therefore, only the regular reception detection pulse is obtained from the gate circuit 25, and the time difference between this and the time point at which the ultrasonic pulse is transmitted is measured. Even if the amplitude of the received ultrasonic pulse suddenly increases and the wave before the regular wave exceeds the reference level, only the regular received detection pulse is obtained from the gate circuit 25, as understood from the above explanation. It will be done. However, when the amplitude of the received ultrasonic pulse suddenly decreases and the regular wave becomes below the reference level, no pulse is output from the gate circuit 25, and therefore the regular received detection pulse is not shown in the figure. , is not output to the time difference measuring circuit connected to the output terminal 26. However, if the regular reception detection pulse is not input,
This time difference measuring circuit, like the conventional time difference measuring circuit, holds the immediately preceding measurement value. In this manner, according to the present invention, the time difference between the normal received detection pulse and the transmitted pulse is measured, so that accurate flow rate measurement of the fluid to be measured is possible. Generally, the normal wave used for the detection signal in the received ultrasonic pulse often uses the wave at the rising edge of the received pulse, for example, the wave at the rising edge as shown in FIG. 2 is used.

For this reason, if the amplitude of the received pulse fluctuates significantly, the output of the comparator 18 may output a wave that is not a regular wave as a regular wave. Since there are fewer waves before the regular wave, the amplitude of the received pulse decreases and is detected as a later wave than the regular wave. There are more opportunities to do so. In other words, there are, for example, only two waves in front of the regular wave, but there are about ten waves in the rear. Therefore, in the time difference detection circuit 23, the conversion gain of the comparator 18 for the pulse from the pulse generation circuit 22 is
If the output of is set equal whether it is early or late, then if the detection of an earlier wave and a later wave occur randomly for a normal wave, in that case, the pulse The output of the comparator often lags behind the pulses of the pulse generation circuit 22, and when averaged by the time constant circuit 24, it is determined that the pulses generated by the pulse generation circuit 22 are ahead, and a control signal to delay them is determined. will appear.

From this point of view, for example, as shown in FIG.
It is preferable to increase the conversion gain for the region Td on the side where the output of the comparator 18 is delayed, and to decrease the conversion gain for the region Td on the side where the output of the comparator 18 is delayed, for example, to set the gain of the latter to about 115 to 1110 relative to the former.

Such a time difference detection circuit 23 can be configured as shown in FIG. 6, for example.

That is, the flip-flops 28 and 29 are reset in advance for each measurement by a reset signal from the terminal 31.
The outputs of flip-flops 29 and 28 are set by the output of comparator 18 and each rising edge from pulse generating circuit 22, respectively. These flip-flops 28, 29
Outputs of mutually opposite polarity and not corresponding to each other are supplied to NAND gates 32 and 33. That is, the Q output of the flip-flop 28 and the O output of the flip-flop 29 are supplied to the NAND gates 32 and 33, respectively. The output side of the NAND gate 32 is connected to the inverting input side of the operational amplifier 35 through an input resistor 34, and the output side of the NAND gate 33 is connected to the operational amplifier 35 through a resistor 36.
connected to the non-inverting input side of the This non-inverting input side is grounded through a resistor 37. Further, a feedback resistor 38 is connected between the output side and the inverting input side of the operational amplifier 35. The output of the operational amplifier 35 is integrated by an integrating circuit 39, and the integrating capacitor 41 of the integrating circuit 39 is reset by closing a switch 42 for each measurement prior to each measurement. now,
If the output pulse of the pulse generation circuit 22 is ahead of the output pulse of the comparator 18, the flip-flop 2
8 is set first, and the output of the NAND gate 32 is at a low level from the rise of the pulse of the pulse generating circuit 22 to the rise of the output of the comparator 18, and this is inverted and amplified by the operational amplifier 35, during which time the output of the NAND gate 32 remains at a high level. The output is supplied to an integration circuit 39 and integrated.

On the other hand, if the pulse of the pulse generating circuit 22 lags behind the rise of the output of the comparator 18, the flip-flop 29 is set first, and the output of the NAND gate 32 remains at a high level.
However, the output of the NAND gate 33 is at a low level during the time difference when the flip-flops 28 and 29 are set, and this low level is supplied to an integrating circuit 39 through an amplifier 35.

In this way, an output with a polarity corresponding to which one is leading with a magnitude proportional to the time difference between the rise of the output pulse of the pulse generation circuit 22 and the rise of the output of the comparator 18 is sent to the output side of the integration circuit 39 with a time difference. It is obtained as the output of the detection circuit 23. The rising edge of the output of the comparator 18 is detected by the pulse generation circuit 22.
In the region earlier than the rise of the pulse, an output is generated at the NAND gate 33, and in this case, the gain of the operational amplifier 35 is determined by the resistance values of the resistors 36 and 37, and the gain is made large, while the comparator 18 If the rise of the output of is slower than the rise of the pulse of the pulse generation circuit 22, the NAND gate 3
2, the gain of the operational amplifier 35 is then determined by the resistance values of the resistors 34, 38 and is chosen to be smaller than in the previous case.

In this way, the time difference detection circuit 23 having the characteristics shown in FIG. 5 is obtained. If the amplitude of the received pulse often instantaneously changes to an abnormally small value, and if no output is obtained from the gate circuit 25 in Fig. 3, this is detected and, for example, a light emitting diode is turned on. It can be understood from the display that a foreign object or air bubble is contained in the channel 11. It is not necessary to directly supply the output of the comparator 18 to the time difference detection circuit 23 to compare the output of the pulse generation circuit 22 and the output of the comparator 18. For example, the output pulse of the received pulse detection circuit 19 (FIG. 4C) ) may be supplied to the time difference detection circuit 23.

That is, as shown in FIG.
The output of the pulse generation circuit 22 and the output of the pulse generation circuit 22 are supplied to a time difference detection circuit 23. In this case, the reception detection pulse (C in FIG. 4) is sent to the gate circuit 2 by the pulse of the pulse generation circuit 22.
5, it is preferable that the rising edge of the pulse 7 coincides with the center of the pulse S of the pulse generating circuit 22. For this purpose, for example, the output of the time difference detection circuit 23 is supplied to an adder circuit 44, where it is added to a constant voltage from a power source 45. 9
The output of this adder circuit 44 is supplied to the time constant circuit 24.

In this manner, the reception detection pulse can be positioned approximately at the center of the pulses of the pulse generating circuit 22 in the steady state. As understood from the explanation of FIG. 2, the time width of the pulse of the pulse generating circuit 22 is set to approximately one cycle of the ultrasonic carrier wave, since a plurality of waves must not be detected at the same time.

If this pulse width is made too short, the gate circuit 25 will not be able to detect it. When no output is obtained from the gate circuit 25, as described above, the time difference measurement values up to that point are held in the same manner as in the prior art. As described above, in the ultrasonic flowmeter using the present invention, even if the amplitude of the received pulse changes instantaneously, the measured value does not undergo large fluctuations corresponding to one wavelength of the ultrasonic carrier wave. Can be measured with high accuracy.

The present invention is applicable not only to ultrasonic flowmeters but also to ultrasonic level meters and other devices that measure the time from the transmission of an ultrasonic pulse to the reception of an ultrasonic pulse with high precision. be able to.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing the relationship between the pipe line and the transducer to explain the ultrasonic flowmeter, Fig. 2 is a waveform diagram to explain the state in which the received detection pulse is extracted from the received ultrasonic pulse, and Fig. 3
The figure is a block diagram showing an example of applying the present invention to an ultrasonic flowmeter, FIG. 4 is a waveform diagram for explaining its operation, and FIG. 5 is a diagram showing an example of conversion gain characteristics of a time difference detection circuit. FIG. 6 is a connection diagram showing an example of a time difference detection circuit, and FIG. 7 is a block diagram showing a partial modification of FIG. 3. 11: Pipe line, 12, 13: Transducer/receiver, 15: Clock pulse input terminal, 16: Transmitting circuit, 17: Receiving circuit, 18
: Comparator, 19: Reception detection pulse generation circuit, 21: Variable delay circuit, 22: Pulse generation circuit, 23: Time difference detection circuit, 25: Gate circuit.

Claims (1)

[Claims] 1 Repeatedly transmitting ultrasonic pulses, receiving the ultrasonic pulses or reflected ultrasonic pulses, detecting a specific wave of the ultrasonic carrier wave in the received ultrasonic pulses, using this as a regular reception detection pulse, and using the ultrasonic pulse as described above. In an ultrasonic measuring device that measures the time from transmitting a sonic pulse to obtaining the regular reception detection pulse, a variable delay circuit that is driven in synchronization with the transmitting of the ultrasonic pulse and can change the delay time; A pulse generation circuit that is driven by the output of the variable delay circuit and generates a pulse with a time width corresponding to approximately one cycle of the carrier wave of the ultrasonic pulse; and a pulse generation circuit that generates an output when the received ultrasonic pulse exceeds a first reference level. a time difference detection circuit for detecting the time difference between the output of the comparator and the output pulse of the pulse generation circuit; and a variable delay circuit for reducing the time difference to zero by the output of the time difference detection circuit. a time constant circuit that generates a control signal for controlling delay time; a reception detection pulse generation circuit that generates a pulse when the received ultrasonic pulse passes through a second reference level after exceeding the first reference level; An ultrasonic measurement device comprising: a gate circuit that is controlled by the output of the pulse generation circuit and passes the output pulse of the reception detection pulse generation circuit as the normal reception detection pulse.