JPS6025543Y2 - ultrasonic flow meter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an ultrasonic flowmeter, and particularly to discrimination of received signals.

An example of a conventional configuration of an ultrasonic flowmeter is shown in FIG.

A pair of shoes 2A, 2B1 and ultrasonic transducers 3A, 3B are attached to the flow path 1 through which fluid flows.

The operation will be explained below using waveforms of each part shown in FIG.

The drive circuit 4B is operated by the signal PA from the synchronization circuit 6, and the ultrasonic vibrator 3B generates sound waves in the fluid in the flow path via the shoe 2B.

After time T1, the sound wave reaches the ultrasonic transducer 3A and generates a signal RA at the output of the receiving circuit 5A.

At this time, switches IIA, 11B, and IIC are connected to the positions shown.

On the other hand, the counter 10 receives a signal from the synchronous circuit 6, starts counting operation, and counts the output of the voltage controlled oscillator 9A.

When the counter 10 counts the output of the voltage controlled oscillator 9A by N pulses, it generates a signal S and supplies it to the time difference voltage conversion circuit 7.ζThe time difference voltage conversion circuit 7 receives the signal RA and the signal -8. Find the time difference between and convert it into a voltage signal I according to the time difference.

This voltage signal {circle around (2)} becomes an input signal to the integrating circuit 8A via the switch 1'IB, and modifies its output signal.

As a result, the output frequency f□ of the voltage controlled oscillator 9A changes in accordance with the time difference. When the time difference between the signal RA and the signal S disappears, the output frequency of the voltage controlled oscillator 9A becomes stable.

- As shown in FIG. 2, the signal PB is generated from the synchronization circuit 6 after an appropriate amount of time has elapsed since the signal PA was generated from the synchronization circuit 6.

At this time, the switches IIA, 11B, and IIC are connected to contacts opposite to those shown in the figure by the output of the synchronous circuit 6.

Therefore, in this case, the drive circuit 4A causes the transducer 2A to emit ultrasonic waves into the fluid, and the ultrasonic waves are received by the receiving circuit 5B via the transducer 2B.

Similarly, the output of the voltage signal oscillator 9B is sent to the counter 10.
When N pulses are counted at , the callan 10 generates a signal S.

The time difference voltage conversion circuit 7 generates a voltage signal (2) according to the time difference between the signal PB and the signal S, and controls the output frequency f2 of the voltage controlled oscillator 9B via the integrating circuit 8B.

In this way, the output frequencies of the two voltage controlled oscillators are controlled alternately, but if this operation is repeated several times, the arrival times of the signal RA or RB and the signal S will become the same.
An equilibrium state is reached in which the signal I is not generated, that is, the outputs of the integrating circuits 8A and 8B do not change.

Now, if the fluid is flowing at a velocity V in the direction shown in Figure 1, then D is the diameter of the tube, θ is the angle between the plane perpendicular to the tube axis and the direction of the sound wave, C is the speed of sound in water.

From this, the flow rate Q becomes , so if we find a signal proportional to the difference f2 - f between the two output frequencies in the output circuit 12, □
The flow rate can be controlled by instructions.

As described above, the ultrasonic flowmeter transmits and receives sound waves through the fluid. Receiving circuits 5A and 5B receive ultrasonic waves transmitted through the road wall.
In the input of □, as shown in FIG. 3, noise, sound and sound waves UAI, and signal sounds and waves UA2 coexist.

Therefore, only the signal sound wave UA2 is extracted and the noise sound wave UA2 is extracted.
1 must be removed to prevent malfunctions in flow measurement.

Therefore, as shown in FIG.
The gate signal GA (GB) must be supplied to the gate signal GA (GB).

If the time width of this gate signal GA (G8) is narrow, only the accurate signal sound wave UA□ will be passed through, thereby further improving the accuracy of flow rate measurement.

Therefore, an object of the present invention is to provide an ultrasonic flowmeter that improves measurement accuracy by narrowing the time width of the gate signal as much as possible.

The present invention is a distant relative of the above-mentioned object by using the integrated value of the output pulses of the oscillator as a reference, and supplying a gate signal with a predetermined time width to the receiving circuit when this integrated value reaches a preset value. It is something.

Specifically, the time N/f from when the synchronous circuit 6 emits the signal PA or PB until when the counter 10 generates the signal S
Noting that □ or N/f2 is almost equal to the propagation time T□ or T2 of the sound wave regardless of the fluid temperature, ) to predict when the signal S will be generated, and based on that, the gate signal GA or GIll is generated.
is generated.

An embodiment of the present invention is shown in FIG.

The same parts as in FIG. 1 are denoted by the same reference numerals and the operations are the same, so a detailed explanation will be omitted.

In this embodiment, the end point detection circuit 18 predicts the time when the signal S will be generated from the content X of the counter 10, and the receiving circuit 17A
Alternatively, the configuration is such that a signal Z for opening the gate is applied to 17B.

Figure 5' showing details of the counter 10 and the receiving circuit 17A or 17B end point detection circuit, and Figure 6, which is an explanatory diagram of its operation.
This example will be explained using figures.

The counter 10 is composed of a grand counter 19, whose contents X are set to an initial value N from the outside by a signal from the synchronous circuit 6 when the signal PA or PB is generated, and whose contents are set by the signal from the voltage controlled oscillator 9A or 9B. signal f1 or f
The content X of the counter 10 is inputted to one side of the digital/rucon notator 20 that constitutes the end point detection circuit 18 and generates the signal S when the content of the counter 10 becomes 0. Setting circuit 21
When the signal Y from the signal X and the signal Y become equal, a signal 2 is generated and is applied to the receiving circuit 17A or 17B.

The one-shot multivibrator 14 in the receiving circuit 17A or 17B that receives the signal Z is brought into conduction with the analog switch 15 to generate a gate signal GA or GB that passes the signal UA or Ur3 through the amplifier 16.

In this way, the frequency f of the voltage controlled oscillator 9A or 9B
1 or f2 is controlled to be N/lower or N/lower 2, so the signal Y from the digital setting circuit 1 can be set to a value close to O, and the width of the gate signal GA or GB can be made very narrow. can.

As described above, according to one embodiment of the present invention, the gate width for removing noise from the signal UA or UB can be made very narrow, and the noise removal effect can be improved.

FIG. 7 shows another embodiment of the present invention, which is even more effective.

In this embodiment, a signal from the power-on timing detection circuit 22 is applied to the analog switch 15 via the OR gate 23.

In the embodiment of FIG. 5, the voltage controlled oscillator 9A or 9B
It is effective when the frequency of the voltage controlled oscillator 9A or 9B is approximately equal to N/T□ or N/lower 2, but the frequency of the voltage controlled oscillator 9A or 9B is not determined when the circuit is powered on, so the gate signal GA or GB cannot be used. It is quite possible that the signal cannot be detected.

Therefore, in this embodiment, the analog switch 15 is kept in the on state by the signal from the power-on timing detection circuit 22 for an appropriate time after the power is turned on, regardless of the signal from the one-shot multivibrator 14, and during that time, the voltage controlled oscillator 9A Alternatively, control the frequency of 9B to N/T□ or N/lower 2, and then use the one-shot multivibrator 14
The noise removal effect is improved by using the gate signal from.

As described above, according to this embodiment, no matter what the frequency of the voltage controlled oscillator 9A or 9B is when the power is turned on, and even no matter what the temperature of the fluid is, after a certain period of time, noise is generated by the narrow gate signal GA or GB. Only the signal that has been removed can be extracted.

When using such gate signals GA and Ga, it is better to have a narrow gate time width in order to increase this effect, but since the sound speed in water changes depending on the temperature at a rate of 5%/20 deg, it is necessary to use weather-resistant fluids. It is necessary to consider the gate width in consideration of the range of temperature changes.

In FIGS. 5 and 7, the analog switch 15 is used as the gate function element, but a digital gate element is used on the output side of the amplifier 16, and the gate signal is generated as described above. It is also possible to control the gate by

In the above explanation, the drive circuits 4A, 4B, and the reception circuit 5At5B
Although two sets of each are shown in the figure, a configuration in which only one set is used may also be used.

Further, although the timing at which the signal S will be generated is predicted from the contents of the counter 10, a separate counter may be newly provided and the output pulses of the oscillator may be counted and predicted by this counter.

As explained above, according to the present invention, since a narrow gate signal can be used, it is possible to obtain an ultrasonic flowmeter that does not malfunction even when installed in a flow path with a lot of acoustic noise and has good measurement accuracy. can.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the configuration of a conventional ultrasonic flowmeter, and FIG. 2 is a diagram illustrating the operation of FIG. 1. FIG. 3 is a diagram for explaining the principle operation of the present invention, FIG. 4 is a diagram showing an embodiment of the present invention, FIG. 5 is a diagram showing one configuration of the receiving circuit in FIG. 4, and FIG. 5 is a diagram showing waveforms of various parts to explain the operation of FIG. 5, and FIG. 7 is a diagram showing another configuration of the receiving circuit in FIG. 4. 4A, 4B...drive circuit, 5A, 5B...
...Reception circuit, 6...Synchronization circuit, 7...
・Time difference voltage conversion circuit, 8A, 8B...Integrator circuit, 9A, 9B...Voltage controlled oscillator, 10...
...Counter, IIA, 11B, IIC...
・Switch, 14... One shot multi-by-break, 15... Analog switch, 16.
...Amplifier, 18...End point detection circuit, 2
2...Power-on timing detection circuit, 23...
・Orgate.

Claims (1)

[Claims for Utility Model Registration] A pair of ultrasonic transducers installed in a flow path through which a fluid flows, and a receiving circuit that receives ultrasonic waves emitted from one transducer into the fluid using the other transducer. J oscillator, a counter that counts the output of this oscillator and generates an output when it reaches a predetermined value, and a time difference conversion circuit that calculates the time difference between the output of this counter and the output of the receiving circuit, In an ultrasonic flowmeter that measures the flow rate of the fluid by changing the output frequency of the oscillator in accordance with the output of a time difference conversion circuit, when the total and integrated value of the output of the oscillator reaches a preset value. An ultrasonic flowmeter characterized in that an end point detection circuit is provided that can input an ultrasonic signal from the vibrator to the receiving circuit for a predetermined time interval when the ultrasonic flowmeter is activated.