JPS5948328B2 - ultrasonic flow meter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an ultrasonic flowmeter, and more particularly to an ultrasonic flowmeter equipped with a time constant circuit suitable for stably averaging measured output.

BACKGROUND OF THE INVENTION FIG. 1 is a circuit diagram of a conventional ultrasonic flowmeter, in which electroacoustic transducers 1a and Ib are acoustically coupled to a conduit 3 through which a fluid 2 flows through contacts 4a and 4b. It has been done.

The electroacoustic transducers 1a and Ib are electrically connected to a flow rate measurement circuit 5, and the voltage output of the flow rate measurement circuit 5 is input to an input terminal T of a time constant circuit 6. Flow rate measurement circuit 5
is a circuit that measures the flow rate (or flow rate) of fluid flowing through the pipe line 3 and outputs a voltage output proportional to the flow rate, and various systems have been devised and put into practical use at present. FIG. 2 is a block diagram of a circuit using a voltage controlled oscillator illustrating the first embodiment. In FIG. 2, electroacoustic transducer elements 1a, I
b are drive circuits 22a, 22b and amplifier circuit 23a, respectively.
, 23b.

The outputs of the amplifier circuits 23a and 23b become one input of the phase comparison and integration circuits 26a and 26b, respectively, and the outputs of the N frequency divider circuits 25a and 25b become one input of the phase comparison and integration circuits 26a and 26.
This is the other input of b. Phase comparison and integration circuit 26a
, 26b serve as inputs to the voltage controlled oscillators 24a, 24b. The output side of the voltage controlled oscillators 24a and 24b is
Drive circuits 22a, 22b, ! ■N frequency divider circuit 25
a, 25b, and further connected to the frequency difference measuring circuit 2T. Further, the output of the timing circuit 21 is transmitted to the drive circuits 22a, 22b and the N frequency divider circuit 25a,
25b. Now, when the fluid 2 flows in the pipe line 3 in the direction of the arrow shown in the figure and the ultrasonic wave propagates through the fluid 2 at an angle θ, the ultrasonic propagation time Ti from the electroacoustic transducer 1a to Ib is expressed by the following equation. It will be done.

T1= (C+ri, sin θ)'cos θ ゜゜゜゜゜' (c Also, the electroacoustic transducer element 1b opposite to the flow direction of the fluid 2
The ultrasonic propagation time T2 from 1a to 1a is expressed by the following equation.

In the configuration shown in FIG. 2, the electroacoustic transducers 1a and 1b emit ultrasonic waves into the fluid 2 in response to signals from the drive circuits 22a and 22b, which are transmitted to the electroacoustic transducers 1b and 1a after times Tl and T2, respectively. and is amplified by the amplifier circuits 23a and 23b.

Assuming that the oscillation frequencies of the voltage controlled oscillators 24a and 24b are Fl and f2, respectively, the 1 drive circuits 22a and 22b and the N frequency divider circuits 25a and 25b start operating simultaneously by the signal from the timing circuit 21, and the N frequency divider circuit 25a
, 25b divide the signals of frequencies Fl and f2 from the voltage controlled oscillators 24a and 24b N times (N is an integer). The phase comparison and integration circuits 26a and 26b are each an amplifier circuit 23.
a, 23b and the outputs of the N frequency divider circuits 25a, 25b are input signals, their phases are compared, and when there is a phase difference, an output proportional to the phase difference is sent out, and the voltage controlled oscillator 24a
, 24b, respectively. The lube is constructed in this way. As a result, the following equation is obtained.
The output Δf of the frequency difference measuring circuit 27 is as follows. From this, it can be seen that Δf is proportional to the flow velocity v of the fluid 2.

In this way, a signal proportional to the flow rate (or flow rate) of the fluid 2 is obtained. In FIG. 1, appropriate braking is applied by passing a signal proportional to the flow velocity of the fluid 2 flowing in the conduit 3 of the flow rate measurement circuit 5 obtained in this way through the time constant circuit 6VC. The time constant circuit 6 has an input terminal 7 and an output terminal 8, between which are a differential amplifier circuit using an operational amplifier 9, an integrating circuit using an operational amplifier 10, and a resistor 11.
, 12, 13, 14, a variable resistor 15, and a capacitor 16 are connected as shown. Now, the resistance values of resistors 11 to 14 and variable resistor 15 are Rll to Rl6R, respectively.
15, the capacitance of the capacitor 16 is Cl6, and the input terminal 7 is
The voltage of e! , the voltage at the output terminal 8 is input to the EOl operational amplifier 9
When the output voltage of is EO, the resistance value Rll~Rl4
Consider the case where there is the following relationship between At this time, the output voltage EO of the operational amplifier 9 is obtained from the following equation. Further, the output voltage EO of the operational amplifier 10 is obtained from the following equation.

From equations (8) and (9), the relationship between e1 and EO is as follows.

Equation (10) shows that the output EO of the time constant circuit 6 becomes a first-order lag of the input e1, and the time constant τ is determined by the equation (11).

The time constant τ can be set to any value by changing the resistance value R15 of the variable resistor 15. The purpose of the time constant circuit 6 is to change the time constant of the output change of the flow rate measuring circuit 5.

In ultrasonic flowmeters, it is important to note that slight changes in flow,
Alternatively, the output of the flow rate measurement circuit 5 fluctuates due to the presence of vortices or bubbles. There are times when it is necessary to follow such fluctuations sequentially, and times when it is desired to obtain a time-averaged output of seconds or more.This depends on the usage conditions of the ultrasonic flowmeter, but as an ultrasonic flowmeter, It is necessary to be able to deal with this by appropriately selecting an output time constant using a time constant circuit. By the way, when the time constant circuit 6 as shown in FIG. 1 is used, this must be done by adjusting the resistance value of the variable resistor 15, which naturally requires a mechanical sliding part, which causes wear of the contacts. etc., resulting in deterioration of characteristics and lower reliability. In particular, in an ultrasonic flowmeter, the time constant setting is often changed, and a configuration using the variable resistor 15 cannot be used stably for a long time.
Also, if bubbles form or foreign objects get into the fluid,
Another drawback was that the ultrasonic waves were reflected and scattered, the received waves changed significantly, and the output of the flow rate measurement circuit was also greatly disturbed. OBJECTS OF THE INVENTION An object of the present invention is to eliminate the drawbacks of the prior art described above, and to provide an ultrasonic flowmeter in which the time constant circuit has no mechanical sliding parts and the output signal is not disturbed even if an abnormality occurs in reception. Our goal is to provide the following.

Summary of the Invention The present invention is characterized in that the time constant of a time constant circuit is adjusted by using a fixed resistor and a switching element connected in series with the fixed resistor, and by controlling the opening/closing period of the switching element. In addition to changing the time constant, the output of the reception abnormality detection circuit is also related to the opening and closing of the switching element.
When an abnormality occurs in the wave reception, fluid flow rate measurement is temporarily interrupted, and at the same time, the normal value immediately before the abnormality is maintained.

Embodiments of the Invention The present invention will be described in detail below with reference to the embodiment shown in FIG. 3 and FIG.

FIG. 3 is a circuit diagram showing an embodiment of the time constant circuit of the present invention, and the same parts as those in FIG.

The difference from FIG. 1 is that a series circuit consisting of a fixed resistor 36 and a semiconductor switch 35 is used instead of the variable resistor 15 in FIG. Then, the semiconductor switch 35 divides its opening/closing period by a frequency dividing circuit 32 that divides the oscillation frequency of the oscillator 31 by the number of divisions set by the setting section 33, and divides the frequency at the output of the frequency dividing circuit 32. Therefore, the monostable oscillator 34 is caused to oscillate and controlled by the output of the monostable oscillator 34. The flow rate measuring circuit 5 is also provided with a reception abnormality detection circuit 41, and the output of the reception abnormality detection circuit 41 and the output of the monostable oscillator 34 are connected to the control input of the semiconductor switch 35 via an AND circuit 42. It's becoming a traffic light.

In FIG. 3, the inverting input terminal of the operational amplifier 9 is connected to the input terminal ? through a resistor 11. It is also connected to the output terminal of the operational amplifier 9 via a resistor 12.

The non-inverting input terminal of the operational amplifier 9 is grounded via a resistor 14, and the operational amplifier 10 is connected via a resistor 13 to the ground.
is connected to the output terminal of A semiconductor switch 35 and a fixed resistor 36 are connected in series between the output terminal of the operational amplifier 9 and the inverting input terminal of the operational amplifier 10.
The inverting input terminal of the operational amplifier 10 is connected to the output terminal of the operational amplifier 10 via the capacitor 16, and the non-inverting input terminal is grounded. The output side of the operational amplifier 10 is connected to the output terminal 8 of the time constant circuit 6. Although 35 is a semiconductor switch, other switching elements may be used. Now, the oscillation frequency of the oscillator 31 is F
O) If the frequency division number set by the setting unit 33 is M (integer) and the oscillation signal width of the monostable oscillator 34 is t, the frequency of the output of the frequency dividing circuit 32 is FO/M, and the monostable oscillator When the oscillation frequency of the monostable oscillator 34 is FO/M and the oscillation period at this time is T, the output waveform of the monostable oscillator 34 is as shown in FIG. 4a. That is, it becomes a rectangular wave oscillation signal with period T and duty cycle t/T. Since the signal in FIG. 4a becomes the control input signal for the semiconductor switch 35,
The semiconductor switch 35 is conductive for a period of time t and is cut off at other times. Such a series circuit of the semiconductor switch 35 and the fixed resistor 36 sets the resistance value of the fixed resistor 36 to R3.
6, it equivalently becomes a resistance with a resistance value t/T·R36. Therefore, the resistance value R1l of the resistors 11 to 141 is
If there is a relationship between Rl4 as shown in equations (6) and (7),
The relationship between equations (10) and (11) above is as follows. (12
) formula shows that the output EO of the time constant circuit 6 becomes a first-order lag of the input e1, which is the same as the formula (10) in the conventional case, but the time constant τ is determined by the formula (13). It can be set by the frequency division number M. In addition, if an abnormality occurs in the received wave signal due to bubbles or foreign matter entering the fluid, flow rate measurement will be stopped for that period, and a signal proportional to the flow rate before the abnormality will be maintained. Continue to output the signal, and when the received signal returns to normal, you can start measuring the flow rate again.

That is, the reception abnormality detection circuit 41 extracts the necessary signal from the flow rate measurement circuit 5, and as shown in FIG. When the signal becomes abnormal, it is configured to output a signal of F7Ol level, and only when the receiving abnormality detection circuit 41 is normally receiving the signal and outputting a signal of 211W level, the time constant The time constant of the circuit 6 is changed.In FIG. 4, (a) is the output of the monostable oscillator 34, and (c) is the output of the AND circuit 42, which becomes the control input signal for the semiconductor switch 35. In this way, when the received signal is normal, the same operation as in FIG. Regardless, the output before the semiconductor switch 35 is cut off is maintained.Then, when the received signal returns to normal, flow rate measurement is started again.Therefore, when the received signal becomes abnormal, flow rate measurement is temporarily stopped. This has the advantage that it is not only possible to interrupt the process, but also to continue to maintain the output before the abnormality occurred.
Note that the flow rate measuring circuit 5 is used instead of the oscillator 31 in FIG.
It is also possible to use a voltage controlled oscillator 24a or 24b.

This is effective when the flow rate measurement circuit 5 of the ultrasonic flowmeter is of the voltage controlled oscillator type, and in this case there is no need to provide the oscillator 31, and other effects are the same as in FIG. 3. Effects of the Invention As explained above, according to the present invention, a highly reliable time constant circuit without mechanical sliding parts can be obtained, and even if the received wave is disturbed by the inclusion of bubbles or foreign matter, the output can be maintained. An ultrasonic flowmeter whose signal is not disturbed can be obtained.

[Brief explanation of the drawing]

Figure 1 is a time constant circuit diagram of a conventional ultrasonic flowmeter, Figure 2 is a block diagram showing an example of the measurement circuit of an ultrasonic flowmeter, and Figure 3 is a time constant circuit diagram of a conventional ultrasonic flowmeter.
The figure is a circuit diagram showing one embodiment of the time constant circuit of the ultrasonic flowmeter of the present invention, and FIG. 4 is a waveform diagram for explaining the operation of FIG. 3. 1a, 1b... electroacoustic transducer element, 2... fluid, 3
...Pipe line, 5...Flow rate measuring circuit, 6...Time constant circuit, 9, 10...Operation amplifier, 24a, 24b...
Voltage control oscillator, 31... Oscillator, 32... Frequency dividing circuit, 33... Setting section, 34... Monostable oscillator, 35
...Semiconductor switch, 36...Fixed resistor, 41...
- Receiving abnormality detection circuit, 42...AND circuit.

Claims (1)

[Claims] 1 at least one pair of electroacoustic transducers, a flow rate measuring circuit connected to the electroacoustic transducing elements, a reception abnormality detection circuit for detecting an abnormality in a received signal of the flow rate measuring circuit, a differential amplification circuit using an operational amplifier; , a time constant circuit comprising a series circuit of a switching element and a fixed resistor, and an integrating circuit using an operational amplifier, and averages the output signal of the flow rate measuring circuit, and the time constant of the time constant circuit is set. An ultrasonic flowmeter comprising a constant setting means, and configured to turn on and off the switching element according to the output of the reception abnormality detection circuit and the output of the time constant setting means.