JPS584766B2 - Ultrasonic fluid measuring device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a fluid measuring device using ultrasonic waves, and is designed to reduce the influence of delay time of a sing-around loop in a sing-around method.

A common ultrasonic fluid measurement device utilizes the principle that the speed at which ultrasonic waves propagate through a stationary fluid is apparently different from the speed at which they propagate through a moving fluid.

One type of fluid measuring device based on such a principle is a sing-around type device.

FIG. 1 is a block diagram showing an example of a conventional single-around type fluid measuring device, in which 1 and 2 are ultrasonic transducers, 3 is a pulse generator, and 4 is an amplifier.

The ultrasonic transducers 1 and 2 convert an electric pulse into an ultrasonic pulse when applied, and conversely convert it into an electric pulse when an ultrasonic pulse is applied. They are arranged so as to form an ultrasonic propagation path on the sides, and constitute a pair of ultrasonic transducers.

Note that the example in FIG. 1 shows an example in which the ultrasonic transducer 1 is used as a transmitter (hereinafter abbreviated as Tx) and the ultrasonic transducer 2 is used as a receiver (hereinafter abbreviated as Rx). ,
With a changeover switch, it is also possible to use complementary switching between Tx and Rx and Rx and Tx.

The pulse generator 3 (hereinafter abbreviated as PG) generates an electric pulse for driving the Tx, and the amplifier 4 (hereinafter abbreviated as AMP) amplifies the electric pulse output from the Rx to a predetermined size. It is for.

These Tx, Rx, PG, and AMP are connected to form a closed circuit, forming a sing-around loop.

Thereby, the ultrasonic signal sent out from Tx propagates through the fluid, is received by Rx, and is converted into an electric pulse.

Then, this electric pulse is amplified by the AMP, then added to the PG, and is again converted into an ultrasonic signal from the Tx and sent out.

In such a configuration, if the distance between Tx and Rx, that is, the propagation length of the ultrasonic signal, is L, the speed of sound in a stationary fluid is C, and the flow velocity of the fluid is ■, then the appearance of the ultrasonic signal in the positive direction of the flow is The propagation time t1 above is as follows, and the apparent propagation time t2 of the ultrasound signal in the opposite direction of the fluid flow is as follows.

Note that in equations (1) and (2), it is assumed that the ultrasonic signal is incident parallel to the fluid flow.

Further, Jo is the sum of delay times of Tx, Rx, AMP, and PG, and is a value that can be determined experimentally.

Although the flow velocity (2) can be determined from the time difference between these propagation times 11 and 12, it is not preferable because it is affected by changes in the sound velocity C.

Therefore, the corresponding frequencies f1 and f2 are determined from these propagation times t1 and t2, respectively, and the flow velocity (2) is determined from the difference between these frequencies.

That is, from equations (1) and (2), f1=1/t1,
As f2=1/t2, it becomes.

However, even in such a conventional single-around method, an error occurs when JoC/L becomes large.

The present invention solves these conventional drawbacks, and will be described in detail below with reference to the drawings.

FIG. 2 is a block diagram for explaining the principle of the present invention, and parts equivalent to those in FIG. 1 are given the same reference numerals.

That is, in FIG. 2, 5 is a delay circuit (hereinafter abbreviated as D), which can set an arbitrary delay time, and is inserted and connected between AMP and PG forming a sing-around loop. ing.

Assuming that the delay time of D is Jd, the total delay time J in the sing-around loop shown in FIG. 2 is as follows: J=Jo+Jd (4).

In such a configuration, the apparent propagation time 11/ of the ultrasonic signal in the forward direction of the flow and the apparent propagation time t2' of the ultrasonic signal in the reverse direction are respectively the first
Similarly to the case in the figure, the following equation is obtained, and the difference Δf1 between the frequencies f1' and f2' corresponding to these propagation times 11' and 12' is as follows.

In this equation (7), the error term is JC/L,
As shown in equation (4) above, the delay time J can be set to an arbitrary time depending on the set time of the delay time Jd of D.

Therefore, the delay time Jd of D is such that J=L/C.
By setting, the above equation (7) becomes △f'-f1'-f2'=V/2L (8)
Therefore, the delay time J of the conventional single-around loop is J.

Errors caused by this can be reduced.

FIG. 3 is a block diagram showing an example of a specific circuit configuration of FIG. 2, and the same parts as in FIG. 2 are given the same reference numerals.

That is, in FIG. 3, 51 is a switch element (hereinafter abbreviated as SW), 52 is an integrator (hereinafter abbreviated as INT), 5
3 is a zero detector (hereinafter abbreviated as DET), and 54 is a flip-flop (hereinafter abbreviated as FF).

The reference voltage Es1 is applied to the ON contact of the SW, and the OFF
A reference voltage Es2 of opposite polarity to the reference voltage Es1 is applied to the contact point.
is applied and the movable contact of this SW is connected to INT.

The output terminal of INT is connected to the input terminal of DET, and the output terminal of mDET is connected to the PG0 human power terminal.

The output terminal of PG is connected to the input terminal of Tx and FF is connected to M.
is connected to the set input terminal S of.

The reset input terminal H of the FF is connected to the output terminal of the AMP, and the non-inverting output terminal Q of the FF is connected to the ON control terminal of the SW.

In such a configuration, the FF is set at the same time as the pulse signal is sent from the PG, and the SW is connected to the ON contact by the output of the FF.

As a result, INT integrates the reference voltage Es1.

Then, when the ultrasonic signal sent from the Tx is received by the Rx and a pulse signal corresponding to the ultrasonic signal is sent from the AMP, the FF is reset and the SW is connected to the OFF contact by the output of the FF. Ru.

As a result, the reference voltage -Es2 of the opposite polarity is applied to INT, and after a certain period of time, the output of INT becomes zero.

DET detects this zero and sends a drive signal to PG.

The PG sends out a pulse signal again in accordance with the drive signal from the DET, the FF is set by this pulse signal, and the same operation is repeated thereafter.

Here, the time when the FF is in the set state, that is, the time when SW is connected to the ON contact, corresponds to the reference voltage Es1, and the time when the FF is in the reset state, that is, when SW is connected to the ON contact.
The time during which the FF contact is connected corresponds to the reference voltage -Es2.

Therefore, by adjusting the reference voltage Es1 or -Es2, J=L/C can be realized.

Note that the reference voltage Es1 or -Es2 may be adjusted so that J=L/C is satisfied approximately at the center of the measurement range.

FIG. 4 is a block diagram showing another example of the specific circuit configuration of FIG. 2, in which the same parts as in FIG. 3 are given the same reference numerals.

That is, in FIG. 4, 55 is a control circuit (hereinafter CT
56 is an adder (hereinafter abbreviated as ADD).

The CTL compares the signal obtained by sampling and holding the INT output signal just before the SW switches to the OFF contact with the reference voltage ER, and generates an output according to the difference, and the output terminal is A.
Connected to one input terminal of DD.

The output terminal of ADD is connected to the OFF contact of SW, and the reference voltage -Es2 is applied to the other input terminal.

Here, the reference voltage ER is J=L at approximately the center of the measurement range.
The reference voltage Es is adjusted so that /C is satisfied.
It is a voltage equal to an integral value signal of 1.

With this configuration, a voltage corresponding to the change in propagation time is sent from the CTL, and a voltage corresponding to the change in propagation time is applied to the OFF contact of the SW, resulting in more accurate operation. can be realized.

In the embodiment, an example in which J=L/C is set has been described, but JoCL/C may be established.

As described above, according to the present invention, it is possible to reduce the influence of the delay time of the sing-around loop in the sing-around method, and to realize a highly accurate superfunctional wave fluid measuring device.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing an example of a conventional device, Fig. 2 is a block diagram for explaining the principle of the present invention, and Figs. 3 and 4 each show a specific example of the circuit shown in Fig. 2. It is a block diagram. 1... Ultrasonic transducer, transmitter Tx, 2... Ultrasonic transducer, receiver Rx, 3... Pulse generator PG, 4...
- Amplifier AMP, 5...Delay circuit D.

Claims (1)

[Claims] 1 Ultrasonic wave transmitter/receiver arranged to form an ultrasonic propagation path between the upstream and downstream sides of the fluid flow whose flow velocity or flow rate is to be measured, and a delay means capable of setting a time. An ultrasonic fluid that forms a around loop, and the delay time of the delay means is set so that the sum of the delay times in the single around loop is approximately equal to the ratio of the propagation length of the ultrasonic propagation path to the speed of sound. measuring device.