JPS6113166B2 - - Google Patents

Description

[Detailed Description of the Invention] This invention relates to a flowmeter using a single-around method (transmitter,
The present invention relates to a one-loop type ultrasonic flowmeter (a method in which a transmission pulse is triggered by a signal received from an ultrasonic pulse propagated a certain distance between receivers), that is, a one-loop method.

The principle commonly thought of for ultrasonic flowmeters is to send ultrasound waves through a fluid medium in two directions, one upstream and one downstream, and propagation through paths of usually equal length. Concerning comparing time. Assuming that the speed of sound is constant, the propagation speed of the wave in the fluid medium is the same in both these paths, but the propagation time varies depending on the flow speed of the fluid medium, and the propagation time is shorter in the downstream path and faster in the upper path. The propagation time is longer in the flow path. From the difference in upstream and downstream propagation times, the flow velocity of the fluid medium can be calculated by time difference techniques. The advantage of using only one acoustic path is that it eliminates the differences caused by multiple path flows.

The basic theory of the time difference technique can be explained as follows. That is, it is assumed that a tube having a uniform flow with a flow velocity v includes two sets of transmission devices facing each other at a distance d , and that the acoustic wave path makes an angle θ with the tube axis. If the speed of sound in a stationary fluid is c , the downstream propagation time t _A and the upstream propagation time t _B are expressed by the following equations.

(1) t _A = d/c + v _p (2) t _B = d/c - v _p where v _p is the velocity component in the direction of the sound wave path, that is, v _p = V·cos θ. If pulses are sent to both paths at the same time, the received signals will arrive at different times by an amount equal to: That is, (3) △t = t _B - _{t A} = 2dv _p /c ² - v _p ² This flow velocity v , and therefore v _p , is in all practical applications of liquids much smaller than the speed of sound c in a stationary fluid. . In these applications, the approximate expression (4) Δt=2dv _p /c ² is very accurate. Therefore, Δt is proportional to v _p , and v _p is determined from the following relational expression. That is, (5) v _p =c ² △t/2d U.S. Pat. No. 3,653,259 describes an ultrasonic flowmeter device based on time difference technology, in which a flow rate is simultaneously transmitted upstream and downstream in a fluid through a propagation path. The delay time of the acoustic pulse is doubled by sending repeating pulses in sing-around fashion. This method has the advantage that very small differences in upstream and downstream transmissions do not need to be measured because of the cumulative effect of combining the delay times between upstream and downstream transmitted pulses for a period of time.

In the device of the aforementioned US patent, it is desirable to utilize only one pair of transmission devices with two sing-around circuits, one upstream and one downstream. In this manner, each transmission device must act as both a transmitter and a receiver. That is, each transmission device must be able to act as a receiver immediately after transmitting a wave. This allowed recovery time is a fraction of the sound wave propagation time, with typical recovery times of 3 or 4 inches (76 mm or
10 microseconds for a water flow meter with a 102 mm tube. To meet this requirement, some types of ultrasonic flowmeter transmission devices, particularly those with metal acoustic windows, have encountered the problem of having to very rapidly attenuate the ringing signal (internal reflection) that occurs after the transmitted pulse. We met. Since the received signal is attenuated while the ringing signal continues constant, it is more difficult to solve the problem with a fluid that strongly attenuates ultrasonic waves.

According to this invention, various problems caused by ringing that occur in a multiplication time difference type ultrasonic flowmeter in a transmission device that works as a receiver and a transmitter can be solved on the upstream and downstream sides of the transmitter and the receiver, respectively. By providing a transmission device consisting of a transmission device, and alternately changing the transmission direction of a continuous train of ultrasonic pulses from the transmitter of one transmission device and the transmission direction of the transmitter of the other transmission device. resolved. In this invention, a number of pulses are first sent upstream for a predetermined period of time, then a number of pulses are sent downstream for the same amount of time, and this process is repeated. The output from this type of doubling time differential ultrasonic flowmeter is determined by comparing two pulse trains of different periods, sing-around pulse trains reaching upstream and downstream. In this invention, since there is only one pulse train at a given time, an auxiliary pulse train is created separately to derive the two signals added to obtain the flow rate, and this auxiliary pulse train is connected to each of the upstream and downstream sing-around pulse trains. be compared. SUMMARY OF THE INVENTION An object of the present invention is to provide a flowmeter that can easily and accurately measure flow rate by eliminating the disadvantages and difficulties of conventional flowmeters of this type due to the ringing signal.

Specifically, according to the present invention, the upstream position and the downstream position are arranged opposite to each other so that they are in sonic contact with the fluid flow and the sound wave passage is aligned with the main component of the fluid flow. A pair of ultrasonic transmission devices are provided. A feedback circuit (sing-around circuit) is provided connecting the output of one transmission device to the input of the other transmission device, so that the signal transmitted from one transmission device to the other is is recirculated through the feedback circuit to one of the transmission devices to produce a unidirectional pulse train through the flow. A switching device is provided for switching the connection of each transmission device to the feedback circuit, thereby directing the unidirectional pulse train downstream from one transmission device with the switching device in one state, and The device can be placed in the other state and transmitted upstream from the other transmission device. It should be noted that a source of auxiliary pulses is provided whose pulse intervals are constant or which have essentially constant characteristics. the switching device in one state to generate a first signal proportional to the accumulation time difference between the auxiliary pulse and the recirculation pulse; and the switching device in the other state generating a first signal proportional to the accumulation time difference between the auxiliary pulse and the recirculation pulse. The first signal and the second signal may be added to derive an output signal proportional to the flow rate of the flow in which the transmission device is disposed. can.

In short, the outline of this invention is as follows.
That is, the present invention provides an ultrasonic flow rate system (two-detector type) equipped with two transmission devices such that pulse trains are transmitted alternately upstream and downstream, and the transmission direction is reversed at a relatively slow rate. It is related to the meter. Each transmission device acts only as a transmitter or receiver during each period of upstream and downstream transmission, i.e., upstream and downstream transmission does not occur simultaneously, resulting in some conventional The ringing problem encountered by ultrasonic flowmeters is resolved,
Conventionally, since the ringing condition remains, there is an effect of eliminating the drawback that the received signal is attenuated.

1, a tube 10 is shown through which a fluid flows in the direction of arrow V with a velocity v . On the wall of this tube 10 and in sonic contact with the fluid therein, two spaced apart ultrasound transmission devices 11 and 12 are provided facing each other. Transmission device 1 downstream from transmission device 12
The ultrasound pulse sent to 1 has a speed equal to c + v _p , where c is the sound velocity in a stationary fluid, and v _p is v cos θ, as described above, where v is the velocity (vector) of the fluid flowing through the tube, and θ is the angle between the tube axis and the sound wave path. If the two transmission devices are in line, as in a tube or free-stream location, θ = 0 and v _p =
It is v. In contrast, when a pulse is transmitted from transmission device 11 to transmission device 12, the wave energy velocity is c-v _p .

The apparatus shown in FIG. 1 includes a relay 14 which is energized for a predetermined period of time, then de-energized for the same period of time, energized again for the same period of time, and so on, and drives this relay. A driver 16 is included. In FIG. 2, waveform a shows the output waveform of the driver 16, and the equal on and off times are represented by ts. The relay 14 has a large number of contacts, the functions of which will be described later.

The sing-around circuit (feedback circuit) 18 of the present invention is shown within the dashed line in FIG. It includes an amplifier 20 having an input terminal connected to receive pulses. The output of this amplifier 20 activates a trigger circuit 24 to generate a trigger pulse (signal) at a predetermined portion of each received ultrasonic pulse (i.e., a burst of ultrasonic vibrations), particularly at the leading edge of the first or second half-wave. generate. This trigger signal activates the astable multivibrator 26 to change state, and the resulting multivibrator output triggers the blocking oscillator 28 to actuate the transmission device 11 or 1 in each case.
2 to complete the regenerative sing-around action.

The operation of the circuit of FIG. 1 can be better understood from FIG. Gating circuit 30 of FIG. 1 produces two gating signals, one appearing on lead 32 and the other appearing on lead 34, delayed by the signal on lead 32 by τ. lead 3
The purpose of delaying the fourth pulse is to prevent the sing-around pulse and the auxiliary pulse from coinciding at the beginning of each pulse train. This will be discussed later.

Gate waveform b in FIG. 2 shows a period t _ON during which the sing-around pulse, auxiliary pulse, and readout circuits are operated so as to be generated repeatedly with a repetition period T. Since the directional switching by relay 14 occurs at a very slow rate, these t _ON periods occur during each period t _S of upstream or downstream transmission. Therefore, most of the total time is represented by a cut in the gate waveform b in FIG. Figure 2 also shows that many sing-around repetitions occur during t _ON .

When a gate pulse of waveform b is first applied to the multivibrator 26, this multivibrator is activated to energize the blocking oscillator 28, thereby causing the burst of ultrasonic oscillator that energized the transmission device 11 to be applied to the transmission device 26. 11 to the transmission device 12. This burst received by transmission device 12 is amplified via lead 36 by amplifier 20 whose output is fed to trigger circuit 24.
The trigger circuit 24 again activates the multivibrator 26 to transmit a second pulse. As a result, as shown in waveform c in Fig. 2,
A series of sing-around pulses with a repeating period t _A results. At the same time, pulses from the gate circuit 30 are applied via lead 40 to a voltage controlled oscillator (VCO) 42 which activates the VOC 42, which generates a series of auxiliary pulses with a repeating period t _C illustrated by waveform d in FIG. produces a pulse. The repetition period t _S of downstream wave transmission is always larger than the repetition period t _A . In the case of upstream transmission, the auxiliary pulse passes through lead 44,
The signal is applied to flip-flop 46. Another input terminal to this flip-flop 46 is connected, in the case of upstream transmission, via a lead 48 and a contact of the relay 14 to a lead 38 from which a sing-around pulse of waveform c emerges. In this way, in the case of upstream transmission, the flip-flop 4
The waveform appearing at the output terminal of 6 is the right half of waveform e in FIG. As can be seen from FIG. 2, the pulse accumulation width during period t _ON of waveform e is proportional to the accumulation time difference between the pulses of waveform c and the pulses of waveform d. When transmitting waves downstream, the relay contacts in FIG. 1 are reversed, and the delayed gate signal on lead 34 is applied to VCO 42, whereas the main gate signal without delay on lead 32 is applied to multivibrator 26. Otherwise, the operation of this device is the same as for upstream transmission. At this time, the phase of the pulse of waveform c is more advanced than that of the auxiliary pulse of waveform d, and the waveform at the output terminal of flip-flop 46 becomes as shown in the left half of waveform e.

This waveform e represents a valid output pulse, and by "valid" we mean that the constant portion of the output pulse on lead 34 equal to the delay τ with respect to the output pulse on lead 32 is not related to the final output; This is not shown in the diagram. In a practical device, the auxiliary or sing-around pulse is delayed by a delay pulse in lead 34 so that the first pulses of waveforms c and d do not coincide. During the downstream transmission period shown in FIG. 2, the output pulse from flip-flop 46 is initiated by a sing-around pulse and terminated by an auxiliary pulse. However, during upstream transmission, the roles of these two pulse trains are reversed. If a delay, τ, is between the two pulse trains producing the output, a waveform consisting of pulses of constant width τ is subtracted from the average flip-flop output to produce the correct valid output, as in the device of U.S. Pat. No. 3,653,259. It is used to extract the voltage that gives .

In order for the flip-flop 46 to work, the early repetition period t _C must be midway between t _A and t _B. This is one of the important points of this invention, so I will explain it in some detail here.
In an ultrasonic flowmeter that utilizes the difference in propagation time between two ultrasonic pulses propagating in the upstream and downstream directions of a fluid, this difference in propagation time is very small compared to the total propagation time of each. Therefore, in a method in which the total propagation times in the upstream and downstream directions are measured separately and the difference between them is determined later, it is necessary to measure each propagation time with very high precision. In order to avoid this, the present invention employs a method of measuring only the time difference without measuring the total propagation time itself. In order to achieve this, we created an auxiliary pulse with a period that was the middle of the total propagation time in the upstream and downstream directions measured at different times, and compared each pulse with this auxiliary pulse. Therefore, the time difference is measured without measuring the total propagation time. For example, here, _if t _B and t _A are the upstream and downstream singaround repetition periods, and t _C is the repetition period of the auxiliary pulse train, then t _B - _{t C} and t _C −t _A is determined separately, and the sum of these is t _B −
Find _tA . Here, t _B -t _C and t _C -t _A are pulse widths, which must always take positive values.
Therefore, t _C must take a value intermediate between t _B and t _A. In order to maintain the repetition period t _C within the correct range under conditions where the speed of sound changes,
It is necessary to control the frequency of the VCO, 42, which is the repetition period t _C . In this regard, the waveform e at the output of flip-flop 46 is applied via lead 45 and the contacts of relay 14 to either low-pass filter 50 or 52 as e _B or e _A , and the output of that filter E _B or E _A is applied to the differential amplifier 54. This differential amplifier 54 is then connected to the VCO 42 by a lead 56.
Apply control voltage to In the example given here, pulse width (△t) _B is greater than pulse width (△t) _A.
Note that this is as shown in FIG. Therefore, if the repetition period t _C is increased, (Δt) _B becomes equal to (Δt) _A , and the respective outputs E _A and E _B transmitted upstream and downstream become equal. The output of flip-flop 46 is also applied to a low pass filter 58 to obtain a total output E _o that includes both upstream and downstream signals.

If t _B and t _A are the upstream and downstream sing-around repetition periods, and t _C is the auxiliary pulse train repetition period, the time difference between the upstream and downstream propagation periods is (6) (△t) _B = t _B - _{t C} (7) (△t) _A = t _C - t _A Therefore, the total time difference is (8) △ t = (△ t) _B + (△ t) _A = t _B - t _A that Therefore, the sum of the individual time differences is the desired amount _tB - _tA and is independent of _tC .

The speed of sound modification of the device of this invention occurs because the sing-around circuit operates at a fixed period (pulse width of the gate waveform). Its output can be expressed as Δt/t _A ·t _B , ie proportional to the fluid velocity component v _p in the direction of the acoustic wave path. Therefore, the output of the sound waves transmitted upstream and downstream of the device of this invention is expressed by the following equation.

(9) E _B =K・d/2・(△t) _B /t _B・t _C (10) E _A =K・d/2・(△t) _A /t _A・t
_C total output E _O is (11) E _O = E _B + E _A = K・d/2・(△t) _B・t _A + (△t) _A・t _B /t _A・t _B・t _C ( 12) E _O =E _B +E _A =K・d/2・(t _B −t _C )t _A +(t _C −t _A )t _B /t _A・t _B・t _C (13) E _O = E _B +E _A = K・d/2・△t/t _A・t _B =K・v _p That is, V _p =1/K (E _B +E _A ) where K is a constant and d is the distance between the transmission devices. It is distance. Therefore, the fluid velocity component v _p and therefore v is
It is proportional to E _B +E _A (the sum of the upstream and downstream pulses of waveform E), regardless of changes in the speed of sound due to temperature changes or other causes.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an embodiment of the present invention.
FIG. 2 is a waveform diagram illustrating the operation of the device shown in FIG. In Fig. 1, a pair of ultrasonic transmission devices...
...11,12, Feedback circuit...1,12
Connection circuit between and 18, switching device...14, 16,
Device that generates auxiliary pulses...40, 42, 4
4,48,46, Device that generates an output signal...
45, 50, 52, 54, 56.

Claims (1)

[Claims] 1 a pair of opposed ultrasonic transmission devices disposed along the flow of the fluid at a position in sonic contact with the fluid;
The electrical output of one of the ultrasound transmission devices is coupled to the electrical input of the other ultrasound transmission device such that a signal propagated from the one to the other ultrasound transmission device generates a unidirectional pulse train through the fluid flow. a feedback circuit that is recirculated to said one acoustic transmission device such that the connection of said respective transmission device to said feedback circuit is reversed so that said unidirectional pulse train is recirculated from one transmission device in one state; A switching device which serves to transmit downstream and upstream from the other transmission device in the other state, the period of the recirculated pulse in one state and the recirculated pulse in the other state by this switching device. a device for generating an auxiliary pulse whose period is controlled to a value intermediate to the period of the circulated pulse; and a device for generating an auxiliary pulse whose period is controlled to a value intermediate to the period of the circulated pulse; A flowmeter having a device for producing an output signal proportional to the sum of the accumulation time differences between the circulated pulse and the auxiliary pulse.