JPH11173880A - Ultrasonic flow meter - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To reduce power consumption, particularly average current consumption of an analog circuit section. Enables the realization of a battery-driven ultrasonic flowmeter. Eliminates unnecessary vibration of the receiving ultrasonic vibrator during time-division driving. Reduce the adverse effect on measurement accuracy due to unnecessary vibration. SOLUTION: At the time of forward measurement, a transmitter / receiver 2 controls transmission and a transmitter / receiver 3 controls reception. Upon receiving the first command signal from the control unit 6, the transmitter driving unit 7 excites the transmitter / receiver 2 to emit ultrasonic waves. The timer 12 transmits the ultrasonic wave to the transducer 3
The set signal is issued just before reaching. Then, the power control unit 9 of the reception wave detection unit outputs an ON signal, and power is applied to the analog amplifier circuit of the reception wave detection unit 8. At the first moment of application, the analog switch SW1 is closed to short-circuit both ends of the transmitter / receiver 3 on the receiving side, thereby preventing unnecessary vibration of the transmitter / receiver 3.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to an ultrasonic flowmeter.

[0002]

2. Description of the Related Art In FIG.
Assuming that the velocity of the flow of the fluid is V, if the propagation direction of the sound wave coincides with the direction along the flow (hereinafter referred to as forward direction), the propagation velocity becomes (C + V), and the direction opposite to the flow (hereinafter referred to as reverse direction). ) Is (CV).

When a pair of transducers 2 and 3 are disposed at a distance L from each other upstream and downstream of the flow tube 1 and ultrasonic waves are emitted from the transducer 2 in the forward direction, the Assuming that the time required for the ultrasonic wave to reach 3 is t ₁ and the time required for the ultrasonic wave to reach the receiver 2 when the ultrasonic wave is emitted from the transmitter 3 in the reverse direction is t ₂ , t ₁ = L / (C + V) (1) t ₂ = L / (C−V) (2)

The above propagation time t of the ultrasonic waves in the forward and reverse directions
₁ and t ₂ were measured, the flow velocity V was calculated from these, and the flow rate was further determined (integrated). The flow velocity V is as described in the above (1),
From equation (2), V = L [(1 / t ₁ ) − (1 / t ₂ )] / 2.

To increase the resolution of the propagation time measurement, 1
The next transmission in the same direction is performed simultaneously with the reception instead of the transmission / reception of the ultrasonic waves, and the transmission / reception in the same direction is repeated a plurality of times (n times) continuously, from the first first transmission to the last n-th transmission. Is measured, and the time from one transmission to reception, that is, the propagation time t ₁ or t ₂ is determined from the measured value.

A receiving wave detecting circuit for detecting a time at which an ultrasonic wave reaches a receiving transmitter / receiver, that is, a receiving device, is mainly constituted by an analog circuit for amplifying a signal and comparing it with a reference level. And the current consumption was large.

[0007] The signal of the receiving transducer is very small,
Since the frequency is large, it is necessary to use a high-performance amplifier to accurately detect the arrival time of the ultrasonic wave, and these amplifiers consume a large amount of current.

As described above, due to the large current consumption of the reception wave detection unit, a battery-driven ultrasonic flowmeter has not been put into practical use in terms of battery life. In order to realize a battery-driven ultrasonic flowmeter, time-division driving of an analog circuit unit that performs amplification of an ultrasonic signal and comparison with a reference level has been proposed. This is to shorten the power-on time of the analog circuit part that consumes a large amount of power as much as possible to reduce the power consumption on average.

In particular, the next transmission in the same direction is performed together with the reception, and the transmission and reception in the same direction are continuously repeated a plurality of times (n times).
In an ultrasonic flowmeter of the type that improves the resolution of the arrival time measurement by measuring a plurality (n) times of the propagation time (also called the arrival time) at a time, the time from the arrival time of the immediately preceding transmission / reception in the continuous transmission / reception Can be predicted (hereinafter also referred to as a reception point), so that the power supply
It is possible to make the N time as close as possible to the receiving point, which has been described by the applicant of the present application in Japanese Unexamined Patent Publication No. Hei 9-133560.
No., disclosed in the official gazette.

[0010]

As the transducer, an ultrasonic transducer such as PZT is used. When the power supply to the analog circuit unit is turned on, a slight but inevitable voltage is applied to the receiver-side transducer connected to the reception-wave detecting circuit, and the receiver-side transducer is temporarily (transiently) turned on. ). For this reason, accurate reception is not possible until the unnecessary vibration stops, and it is necessary to turn on the power of the analog circuit section as quickly as possible so that the unnecessary vibration is attenuated and does not adversely affect the reception.
This is a factor that makes it impossible to shorten the N time below a certain value, which is an obstacle to reducing the power consumption of the ultrasonic flowmeter.

In the reception wave detection circuit, a specific wave for each reception, for example, a zero-cross point of a third wave is detected and set as a reception point. However, the unnecessary vibration, which may be called noise, distorts a reception signal and generates a zero-cross point. Is moved, which is a factor of lowering the measurement accuracy of the arrival time. In particular, when the flow velocity is stable, the arrival time at each time is almost the same, and the unnecessary vibration is mixed with the received signal at almost the same timing (that is, the same phase) every time. Therefore, an adverse effect cannot be eliminated by averaging by repetition like ordinary random noise. Therefore, the unnecessary vibration has been a major obstacle in improving the accuracy of the ultrasonic flowmeter.

An object of the present invention is to provide an ultrasonic flowmeter capable of eliminating these obstacles.

[0013]

In order to achieve the above object, according to the first aspect of the present invention, at least one pair of ultrasonic transducers, which work on both a transmitting side and a receiving side, are provided, and the flow of the fluid is controlled. An ultrasonic flowmeter that transmits and receives ultrasonic waves from upstream to downstream and from downstream to upstream, and obtains the flow velocity and the flow rate from the arrival time in each direction.First, the transmitter on the transmitting side is transmitted, and the transmitting and receiving side on the receiving side is transmitted. When the received wave detection unit which receives the signal of the wave detector detects the received wave, the transmitter / receiver on the transmitting side is transmitted again, and this is repeated a fixed number of times (n times). The time until the reception of the number of times (the n-th time), that is, n times of the arrival time, is collectively measured, and the flow velocity and the flow rate are obtained from the result. The reception wave detection unit mainly includes an amplifier. It consists of analog circuits that Is supplied immediately before the reception wave arrives, and is cut off when the reception wave is detected, and both ends of the reception-side transducer are electrically short-circuited or opened. The ultrasonic flowmeter is characterized in that a switching element is arranged, and the moment when the power to the analog circuit unit is turned on is in a short-circuit state, and thereafter, when a reception wave arrives, it is in an open state.

When power is supplied to the analog circuit section, it is unnecessary to apply a voltage to the connected receiving-side transducer due to an imbalance between the rise of the positive power supply and the negative power supply of the amplifier. This is the cause of the vibration.

According to the present invention, when the power supply to the analog circuit section is turned on, the voltage is not applied to the transmitter / receiver since both ends of the transmitter / receiver on the receiving side are short-circuited. Therefore, the reception becomes possible in a short time without unnecessary vibration, and the power of the analog circuit unit can be turned on at a time as close as possible to the expected reception time (the expected reception point). As a result, the power supply O
Reception is possible even if the N period is extremely short, and the average current consumption can be reduced.

According to a second aspect of the present invention, there is provided at least one pair of ultrasonic transducers that work on both the transmitting side and the receiving side, and transmit and receive ultrasonic waves in a fluid flow from upstream to downstream and from downstream to upstream. An ultrasonic flowmeter that determines the flow velocity and the flow rate from the arrival time in each direction, first transmits the transmitter / receiver on the transmission side, and receives the signal from the receiver / receiver on the reception wave detector to receive the signal. When a wave is detected, the transmitter / receiver on the transmitting side is transmitted again, and this is repeated a certain number of times (n times), and the time from the first transmission to the reception of the certain number of times (n times), that is, the arrival time N times as large as
Based on the result, the flow velocity and the flow rate are obtained, and the reception wave detection unit is mainly configured by an analog circuit centered on an amplifier, and the power is supplied immediately before the reception wave arrives every time. A first switching element that is cut off when a received wave is detected, and electrically shorts and opens both ends of the receiving-side transducer; and a signal of the receiving-side transducer. And a second switching element for connecting / disconnecting the analog switching unit to / from the analog circuit unit. When the power supply to the analog circuit unit is turned on, the first switching element is short-circuited and the second switching element is disconnected. State, and when the reception wave arrives thereafter, the first switching element is set to the open state and the second switching element is set to the connected state.

According to the present invention, the power supply of the analog circuit is turned on.
In some cases, the signal of the receiving-side transducer is separated from the analog circuit section, and there is no transient adverse effect when the power is turned on, which is more effective.

According to a third aspect of the present invention, in the ultrasonic flowmeter of the first or second aspect, the switching element is controlled with a blunt waveform. Generally, a CMOS analog switch or the like can be used as a switching element. However, ON, OF of this type of switching element
The control signal of F may newly cause unnecessary vibration. This is because the control signal is applied to the receiving transducer through a very small capacitance.

According to the present invention, the control is performed with a blunted waveform, thereby preventing the control signal itself from causing unnecessary vibration. The invention of claim 4 provides at least one pair of ultrasonic transducers that work on both the transmitting side and the receiving side, and transmits and receives ultrasonic waves from upstream to downstream and from downstream to upstream in the flow of fluid. An ultrasonic flowmeter that determines the flow velocity and the flow rate from the arrival time in each direction, first transmits the transmitter / receiver on the transmitting side, and the received wave detector that receives the signal from the receiver / receiver detects the received wave. Then, the transmitter / receiver on the transmitting side is caused to transmit again, and this is repeated a fixed number of times (n times), and the time from the first transmission to the reception of the fixed number of times (n times), that is, n times the arrival time. Are collectively measured, and the flow velocity and the flow rate are obtained from the result, so that the arrival time of each of the n times of transmission and reception can be measured once, and the reception wave detecting unit mainly comprises: Is composed of analog circuits centered on amplifiers. It has, in its power, first of all
It is turned on a fixed time after the first transmission, and turned off when a received wave is detected. From the next transmission, it is turned on after a certain time has elapsed from the previous arrival time minus the previous arrival time. An ultrasonic flowmeter configured to be turned off when a reception wave is detected again and thereafter to continue the operation, wherein the constant time is changed for each transmission so as to have various values within a constant range. It is.

When the power of the analog circuit section is turned on, unnecessary vibration of the same shape occurs every time. Turn on the power in anticipation of the receiving point
In the case of N, if the flow velocity is stable, the reception point comes at the same timing with respect to the waveform of the unnecessary vibration, which is a major factor of the error.

According to the present invention, by shifting the power-on timing of the analog circuit unit every time with respect to the received wave, the influence is averaged during n repetitions and approaches zero, thereby improving the measurement accuracy.

According to a fifth aspect of the present invention, in the ultrasonic flowmeter of the first, second or third aspect, the reception wave detecting section is mainly constituted by an analog circuit mainly including an amplifier, and the power supply thereof is: It is supplied immediately before the received wave arrives each time, and is turned on after a certain period of time from the first transmission so that it is turned off when the received wave is detected, and turned off when the received wave is detected.
It will be turned on when a certain time has been subtracted from the previous arrival time from the current call.
Then, when the received wave is detected again, the signal is turned off, and thereafter, the operation is continued. The constant time is changed for each transmission so as to have various values within a certain range. It is characterized by suppressing unnecessary calls.

[0023]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, preferred embodiments of the present invention will be described with reference to the drawings. [Embodiment 1] The embodiment of FIG. 1 corresponds to the first aspect of the present invention.

A pair of transducers 2 and 3 are ultrasonic transducers such as PZT, which can be used for both transmission and reception. When one transducer is used for transmission, the other transducer is used. Is used for reception.

Switching between transmission and reception is performed by switching the changeover switches 4 and 5 with a transmission / reception switching signal from the control unit 6. In the state of FIG. 1, the transmitter / receiver 2 is connected to the transmitter driver 7 and is used as a transmitting side. The transducer 3 is connected to the received wave detector 8 and is used as a receiving side.

The two transducers 2 and 3 transmit and receive ultrasonic waves in the fluid from upstream to downstream and from downstream to upstream. The received wave detector 8 is turned on by the received wave detector power controller 9.
When the signal is “ON”, the power supply of the analog circuit unit, which is a part of the configuration, is turned on. When a reception wave is detected from a signal from the connected transmitter / receiver 3 on the reception side, the reception wave is received. Outputs a detection signal.

When the transmitter driver 7 receives the first transmission command signal from the controller 6, it first drives the transmitter / receiver 2 on the transmitting side, and thereafter every time it receives a received wave detection signal from the received wave detector 8. Drive the same transducer.

The first counter 10 counts the reception wave detection signal from the reception wave detector 8 and outputs the nth reception wave detection signal. This counter 10 has a control unit 6
Reset by the first transmission command signal.

The second counter 11 measures the time from the first transmission command signal to the nth received wave detection signal. The control unit 6 reads the time (count value). In this example, the count value is cleared to zero by the first transmission command signal, and counting of the reference clock from the reference clock generator, which is a component, is started.

The control section 6 switches the roles of the two transducers 2 and 3 by inverting the transmission / reception switching signal at regular intervals. After each switching, a first transmission command signal is output at a time when noise or the like due to the switching is settled every time. When the n-th received wave detection signal is input, the measured value (count value) of the counter 11 is read, and the flow rate flow rate is calculated and displayed using the measured value in the opposite direction performed immediately before. .

When the first transmission command signal is input from the control unit 6, the timer 12 starts counting time from that point in time, and the analog circuit starts from a certain time determined as the minimum possible ultrasonic arrival time. When a set signal is output after a time obtained by subtracting the unit stabilization time (time from when the power is turned on until reception becomes possible), and then a reception wave detection signal from the reception wave detection unit 8 is input, the time to that point is calculated. At the same time, the time counting is started from zero again.

Then, a set signal is output when a time obtained by subtracting the analog circuit stabilization time from the stored time has passed, and then a reception wave detection signal from the reception wave detection unit 8 is input. And the time counting is started again from zero. Then, a set signal is output when a time obtained by subtracting the analog circuit section stabilization time from the stored time has elapsed, and this is repeated thereafter.

SW1 is an analog switch as a switching element for electrically short-circuiting and opening both ends of the receiving-side transducer.
Is applied via the delay circuit 13 and the inverter 14 for operation. The illustrated lower end of the analog switch SW1 is grounded to an analog ground. The switch SW1 is connected to both ends of the transmitter / receiver 3 or 2 on the receiving side by the changeover switch 5.

FIG. 2 shows the configuration of the embodiment of the timer 12. When the first transmission command signal is input, the counter 1
5 is reset and counts the reference clock from the clock generator 16 to start counting time, and the memory 1
In 7, a value determined as a minimum arrival time considered from the distance between the transducers and the sound speed is preset (this value is output).

This value is input to the A input of the subtractor 18. A constant value equivalent to the analog section stabilization time is input to the B input, and a value corresponding to AB is input to the comparator 1.
9 is output. The counter 15 counts the reference clock, and this count value is another input of the comparator 19, and the comparator 19 outputs a coincidence signal when the two inputs become equal.

When the received wave detection signal is input, the count value at that moment corresponding to the arrival time is stored in the storage unit 17, and is reset at the same time and starts counting from zero again (reset after storage). ). Therefore, this time, when the count advances to a count value corresponding to a time obtained by subtracting the analog section stabilization time from the previous arrival time, a coincidence signal is output. Thereafter, the operation when the reception wave detection signal is input is the same. Thus, the above-described function is realized.

Power supply control unit 9 shown in FIG.
Is an ON signal which receives a coincidence signal from the timer 12 as a set signal and a received wave detection signal from the received wave detector 8 as a reset signal. The ON signal is "ON" by the set signal and is "OFF" by the reset signal. Is output to the reception wave detection unit 8. As a result, the power supply of the analog circuit unit of the reception wave detection unit 8 is supplied (ON) immediately before the reception wave arrives, and is cut off when the reception wave is detected.

The ON signal is also input to the delay circuit 13. In the embodiment, the CMOS analog switch SW1 is used as a short-circuit element. The ON signal was delayed by a delay circuit so as not to coincide with the ON of the analog circuit section, and further inverted by the inverter 14 to obtain a control signal for the analog switch SW1. Thus, the normally short-circuited analog switch SW1 is short-circuited at the moment when the power supply to the analog circuit section is turned on, and becomes open immediately after that, and becomes open when a reception wave arrives.

The analog circuit stabilization time is set to a value slightly longer than the actual stabilization time in consideration of the fact that the flow velocity becomes faster during the measurement. Further, the received wave detection unit power supply control unit 9 does not output an ON signal when receiving the nth received wave detection signal from the counter 10. That is, thereafter, no reception is performed, and the transmission / reception cycle is interrupted there.

[Embodiment 2] FIG. 3 shows an embodiment corresponding to the second aspect of the present invention. An analog switch SW2 that operates in the opposite direction to that of the analog switch SW1 is provided to make it more difficult for the effect of turning on the power to be transmitted. 13A is a buffer.

[Embodiment 3] FIG. 4 shows a third embodiment of the present invention in which the control signal of the analog switch SW1 is transmitted to the CR circuits 14B, 1B.
By shading with 4C, it is possible to prevent the control signal from causing unnecessary vibration.

[Embodiment 4] FIG. 5 shows an embodiment of a timer 12A used in claims 4 and 5. The lower 3 bits of the constant value corresponding to the analog circuit section stabilization time which is the B input of the subtractor is the output of the counter 20 of the 3-bit counter. The upper bits have a value that can secure the analog circuit section stabilization time regardless of the value of the three bits. Further, the counter 20 counts the reception wave detection signal.
Count up as 3, 4, 5, 6, 7, 0, 1,. Thus, the value of the input B changes by one every time within the range of the count value 8.

In the case of the embodiment, the frequency of the reference clock oscillator 16 is 2 MHz, and the frequency of the ultrasonic transducer used is approximately 2 MHz.
It is 50 kHz and the time for 8 clocks is made to coincide with one cycle. Similarly, the receiving point comes equally in one cycle of the unnecessary vibration which is considered to be about 250 kHz, and the influence disappears efficiently by averaging by repetition. I am aiming.

[0044]

Since the ultrasonic flowmeter of the present invention is configured as described above, the power ON time (operating time) of the reception wave detecting section mainly including an analog circuit consuming a large amount of current can be shortened. Power consumption can be reduced.

Further, it is possible to prevent the unnecessary vibration noise after the power is turned on from being synchronized with the received wave, and to substantially average and reduce the error due to the noise by repeating n times, thereby contributing to the improvement of the accuracy of the flowmeter. I do.

[Brief description of the drawings]

FIG. 1 is a block diagram of an embodiment of the present invention.

FIG. 2 is a block diagram of a timer shown in the block diagram of FIG. 1;

FIG. 3 is a block diagram of another embodiment of the present invention.

FIG. 4 is a block diagram of still another embodiment of the present invention.

FIG. 5 is a block diagram of a main part embodiment of the present invention.

FIG. 6 is a schematic diagram illustrating the principle of an ultrasonic flowmeter.

[Explanation of symbols]

2,3 Ultrasonic wave transmitter / receiver 4,5 Transmission / reception switch 6 Control unit 7 Transmitter driving unit 8 Received wave detection unit 9 Received wave detection unit Power supply control unit 10,11 Counter 12,12A Timer 14B, 14C CR circuit SW1 , SW2 Switching element (analog switch)

Claims (5)

[Claims] At least one pair of ultrasonic transducers that work on both a transmitting side and a receiving side are provided to transmit and receive ultrasonic waves in a fluid flow from upstream to downstream and from downstream to upstream. An ultrasonic flowmeter that obtains the flow velocity and the flow rate from the arrival time of the ultrasonic wave, transmits the transmitter / receiver on the transmission side, and when the reception wave detection unit that receives the signal of the reception side transducer detects the reception wave, again The transmitter / receiver on the transmitting side is made to transmit, and this is repeated a certain number of times (n times), and the time from the first transmission to the reception of the certain number of times (n times), that is, n times the arrival time, is collected. Measured, the flow velocity and the flow rate are determined from the result, the received wave detection unit is mainly configured by an analog circuit centered on an amplifier, the power supply, every time immediately before the received wave arrives And the received wave is detected. A switching element that electrically shorts or opens both ends of the receiving transducer is arranged, and the moment when the power supply to the analog circuit is turned on is in a short-circuit state. An ultrasonic flowmeter, which is opened when a reception wave subsequently arrives. 2. At least one pair of ultrasonic transducers, which act on both the transmitting side and the receiving side, transmit and receive ultrasonic waves in a fluid flow from upstream to downstream and from downstream to upstream. An ultrasonic flowmeter that determines the flow velocity and the flow rate from the arrival time of the ultrasonic wave transmitter, first transmits the transmitter / receiver on the transmission side, and when the reception wave detection unit that receives the signal of the reception side transducer detects the reception wave, The transmitter / receiver on the transmitting side is made to emit again, and this is repeated a fixed number of times (n times), and the time from the first transmission to the reception of the fixed number of times (n times), that is, the arrival time n
The received wave detection unit is mainly composed of an analog circuit centered on an amplifier, and the power supply thereof receives the received wave every time. A first switching element that is supplied immediately before reaching, and is cut off when a reception wave is detected, and electrically shorts or opens both ends of the reception-side transducer. A second switching element for connecting / disconnecting the signal of the receiving side transducer to / from the analog circuit unit is arranged, and at the moment when the power to the analog circuit unit is turned on, the first switching element is short-circuited, and The second switching element is disconnected, and when a reception wave arrives thereafter, the first switching element is opened and the second switching element is connected. Sound flow meter. 3. The ultrasonic flowmeter according to claim 1, wherein the switching element is controlled with a blunt waveform. 4. At least one pair of ultrasonic transducers, which work on both the transmitting side and the receiving side, transmit and receive ultrasonic waves in a fluid flow from upstream to downstream and from downstream to upstream. An ultrasonic flowmeter that determines the flow velocity and the flow rate from the arrival time of the ultrasonic wave transmitter, firstly transmits the transmitter / receiver on the transmission side, and when the reception wave detector that receives the signal of the reception side transducer detects the reception wave, The transmitter / receiver on the transmitting side is made to emit again, and this is repeated a fixed number of times (n times), and the time from the first transmission to the reception of the fixed number of times (n times), that is, the arrival time n
The times are measured collectively, and the flow velocity and the flow rate are obtained from the result. The arrival time of each of the n times of transmission and reception can be measured once. It is mainly composed of an analog circuit centered on an amplifier, and its power supply is first turned on a fixed time after the first transmission, and when a received wave is detected, the power is turned on.
From now on, it is turned on when a certain time has been subtracted from the previous arrival time, and turned off when a received wave is detected again. An ultrasonic flowmeter configured to change the constant time for each transmission so as to have various values within a constant range. 5. The received wave detecting section is mainly composed of an analog circuit mainly composed of an amplifier, and its power is supplied immediately before the received wave arrives each time, and is cut off when the received wave is detected. As shown in the figure, the signal is first turned on a fixed time after the first transmission, and turned off when a received wave is detected. From the next transmission, a certain time is subtracted from the previous arrival time from the current transmission. ON after a lapse of a given time, and OFF again when a received wave is detected, and thereafter continue, and the constant time is changed for each transmission so as to have various values within a constant range. Claims 1 and 2
Or the ultrasonic flowmeter according to 3.