JP2010066083A - Method for measuring flow of fluid - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To make the power-on timing of an amplification means approach the receiving timing of an ultrasonic signal in order to save power. <P>SOLUTION: At first set time immediately before the end of a propagation time of an ultrasonic signal estimated by a propagation time estimation means 14, power supply by a power source 7 is started when a high-resistance resistor is selected as a connecting resistor between a receiving-side ultrasonic transmitter 2 or a receiver 3 and the amplification means 9. and vibration noise generated on that occasion between terminals of the receiving-side ultrasonic transmitter and the receiver is rapidly attenuated. After that, at a second set time, the connecting resistor between the receiving-side ultrasonic transmitter and the receiver and the amplification means 9 is switched to a low-resistance resistor to receive the ultrasonic signal. Consequently, the start timing of the power supply to the amplification means is made to approach the receiving timing. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a flow measurement device that measures a physical quantity such as a flow velocity and / or a flow rate of a fluid by measuring a propagation time of an ultrasonic signal.

  Conventionally, in this type of flow meter, a technique called the reciprocal difference method is widely known. In this method, ultrasonic transmitters / receivers are arranged on the upstream and downstream sides of the fluid flow direction, respectively, and the time during which the ultrasonic waves propagate between the two ultrasonic transmitters / receivers, that is, the propagation time is measured. This is based on the fact that the propagation time in the direction is different from the propagation time in the reverse direction.

  More specifically, the measurement is performed based on the property that the reciprocal difference of the mutual propagation time is proportional to the flow rate.

  FIG. 3 shows a flow measurement device using the reciprocal difference method, and a pair of ultrasonic transceivers 102 and 103 are arranged on the upstream and downstream sides so that the ultrasonic wave obliquely crosses the fluid flowing through the fluid flow path 101. The reception and transmission conditions of these ultrasonic transceivers 102 and 103 are controlled by the control unit 104, and the ultrasonic propagation time difference between the ultrasonic transceivers 102 and 103 is measured by the measurement unit 105, Originally, the flow velocity and flow rate of the fluid are calculated by the calculation unit 106.

  Here, the sound velocity is C, the flow velocity is v, the distance between the ultrasonic transmitters / receivers 102 and 103 is L, the angle formed by the ultrasonic wave propagation direction and the fluid flow direction is θ, and the upstream ultrasonic transmitter / receiver. When t1 is the propagation time when the ultrasonic wave is transmitted from 102 and received by the ultrasonic wave transmitter / receiver 103 on the downstream side, and t2 is the propagation time in the reverse direction, t1 and t2 can be obtained by the following equations. .

t1 = L / (C + v cos θ) (1)
t2 = L / (C−v cos θ) (2)
Equation 1 and Equation 2 are modified, and the flow velocity v is obtained by Equation 3 below.

v = L · (1 / t1-1 / t2) / 2 cos θ (3)
The flow rate of the fluid can be obtained by multiplying the value obtained by Equation 3 by the cross-sectional area of the fluid flow path 101.

  As is apparent from the above-described measurement principle, the ultrasonic flow measuring device has a structure that does not have a mechanical moving part, so that it is a mechanical so-called membrane that is currently widely used in domestic and overseas gas meters. It is expected to replace the gas meter.

  Most gas meters are installed outdoors where commercial power cannot be secured, and, unlike consumer appliances, are required to be maintenance-free.

  Therefore, it is necessary to guarantee operation for 10 years by battery operation. Therefore, it is desired that the power consumption be extremely small.

  On the other hand, the ultrasonic signal output from the ultrasonic transmitter / receiver is generally extremely attenuated in gas. For example, when the level of the transmission wave is 5v, the level of the reception wave may be attenuated to the μv order.

  As described above, it is necessary to amplify a very small reception signal by using an amplifier, and there is a situation in which an increase in power consumption cannot be avoided.

  From the above, in order to satisfy the long life, it is essential to shorten the operation time of the receiving circuit including the amplifier as much as possible.

  As a method of shortening the operation time, a method of executing power supply only near the reception point of the ultrasonic signal can be considered. In such a configuration, when the circuit power is turned on, a transient large voltage fluctuation occurs at both ends of the ultrasonic transmitter / receiver, which causes unnecessary vibration in the ultrasonic transmitter / receiver. Since this unnecessary vibration is superimposed on the received signal, there is a problem that the measurement accuracy is deteriorated.

As means for solving this problem, at the start of power supply to the receiving circuit, the receiving-side ultrasonic transmitter / receiver is disconnected from the receiving circuit, and after the power supply voltage is stabilized, the transmitter / receiver is connected to the receiving circuit. The thing is considered (for example, refer patent document 1).
Japanese Patent Laid-Open No. 11-173880

  However, even in the configuration as described above, the transient change applied to both ends of the transmitter / receiver at the moment when the receiving-side ultrasonic transmitter / receiver is connected to the receiver circuit is not completely eliminated, and a slight but unnecessary vibration is not generated. Inviting is inevitable.

  On the other hand, as described above, since the attenuation of the ultrasonic signal propagating in the gas is particularly severe, it is necessary to considerably increase the amplification factor of the amplifier circuit.

  Therefore, the slight unnecessary vibration that occurs when the receiving-side ultrasonic transmitter / receiver is connected finally results in a large amplification.

  Therefore, before the received signal arrives, in addition to the power supply voltage stabilization wait time, a wait time is required until the unnecessary vibration that occurs at the time of connecting the receiving side ultrasonic transceiver and the receiving circuit is settled, There was a problem that the power supply time for the receiving circuit could not be shortened as much as expected, and the power consumption could not be reduced as intended.

  The present invention solves such a conventional problem and aims to shorten the power supply time to the receiving circuit as much as possible.

In order to solve the above-described conventional problems, the fluid flow rate measuring device of the present invention is set to at least a pair of ultrasonic transmitters / receivers disposed on the upstream side and the downstream side of the fluid flow path, and to the reception side. Amplifying means connected to the one ultrasonic transceiver via a load resistor, a power switch for switching supply / stop of power to the amplifying means, and the one ultrasonic transceiver set on the receiving side And a resistance value switching means for switching the connection resistance value of the amplification means, a reception determination means for judging reception of the ultrasonic signal based on the output of the amplification means, and a propagation time from transmission to reception of the ultrasonic signal. Timer to measure, propagation time prediction means for determining the next predicted propagation time based on the past propagation time measured by the timer, and reception control for controlling the power switch and resistance switching means And the reception control means starts supplying power to the amplification means by the power switch at a first set time before the predicted propagation time, and the first set time and the predicted propagation time The connection resistance between the ultrasonic transducer / amplifier and the amplifying unit is set to the reception / reception side by the resistance value switching unit at a second set time in between. By switching the resistance value to a low resistance value that can be regarded as almost zero, the power supply start timing of the amplifying means is brought close to the reception timing.

  Since the fluid flow measuring device of the present invention can make the power supply start timing of the amplifying means closer to the reception timing, highly accurate measurement is possible while maintaining power saving performance.

  According to a first aspect of the present invention, at least a pair of ultrasonic transmitters / receivers arranged on the upstream side and downstream side of the fluid flow path and the one ultrasonic transmitter / receiver set on the receiving side are connected via a load resistor. Amplifying means, a power switch for switching supply / stop of power to the amplifying means, and a resistance value switching means for switching the connection resistance value of the one ultrasonic transceiver set on the receiving side and the amplifying means A reception determination unit that determines reception of an ultrasonic signal based on an output of the amplification unit, a timer that measures a propagation time from transmission to reception of the ultrasonic signal, and a past propagation time measured by the timer. Propagation time prediction means for determining the next predicted propagation time based on the original, and reception control means for controlling the power switch and resistance switching means, the reception control means is based on the predicted propagation time. Power supply to the amplifying means is started by the power switch at a previous first set time, and the resistance value switching means at the second set time between the first set time and the predicted propagation time. The connection resistance between the ultrasonic transmitter / receiver and the amplification means is switched from a high resistance value equivalent to the impedance of the one ultrasonic transmitter / receiver set on the receiving / receiving side to a low resistance value that can be regarded as almost zero.

  Therefore, just before the predicted propagation time, first, the receiving-side ultrasonic wave generated when the power is supplied by turning on the power of the amplifying unit with the connection resistance between the receiving-side ultrasonic transmitter / receiver and the amplifying unit being high resistance. After attenuating vibration noise between the transmitter and receiver terminals rapidly, the connection resistance with the amplification means is switched to a low resistance and the ultrasonic signal is received, so the power supply start timing of the amplification means is brought close to the reception timing. Therefore, it is possible to measure with high accuracy while maintaining power saving performance.

  In the second invention, particularly in the first invention, the transmission / reception switching which enables measurement in both the forward direction and the reverse direction of the flow by switching the roles of the transmission side ultrasonic transmission / reception unit and the reception side ultrasonic transmission / reception unit. Means and a computing means for calculating a fluid flow velocity and / or flow rate based on a propagation time measured by a timer, and the reception control means includes a first based on the individual estimated propagation time in the forward direction and the reverse direction of the flow. And the second set time are set, so by setting the power-on timing separately in the forward and reverse directions of the flow, the optimal control timing can be set regardless of the flow rate fluctuation, and power saving performance The flow can be measured with higher accuracy while maintaining

  According to a third aspect of the invention, particularly in the first or second aspect of the invention, the temperature estimation means for estimating the ambient temperature of the apparatus based on the measured propagation time, and the reception-side ultrasonic transceiver according to the estimated temperature of the temperature estimation means Impedance estimation means for estimating impedance, and the reception control means is configured to control the value on the high resistance side of the connection resistance of the reception-side ultrasonic transceiver and amplification means according to the output of the impedance estimation means. The connection resistance between the receiving-side ultrasonic transmitter / receiver and the amplification means can be optimized according to the temperature characteristics of the ultrasonic transmitter / receiver.

  Embodiments of the present invention will be described below with reference to the drawings. The embodiments do not limit the present invention.

(Embodiment 1)
In FIG. 1, a pair of ultrasonic transmitters / receivers 2, 3 are arranged on the upstream / downstream side so that the ultrasonic wave obliquely crosses the fluid flowing through the fluid flow path 1.

  These ultrasonic transmitters / receivers 2 and 3 are connected to a subsequent processing block via transmission / reception switching means 4 that reverses the role of transmission / reception.

  The transmission / reception switching means 4 is composed of four switches. When the contact a is closed, the ultrasonic transmitter / receiver 2 is on the transmission side, the ultrasonic transmitter / receiver 3 is on the reception side, and when the contact b is closed, the ultrasonic transmitter / receiver 3 is closed. Is the transmitting side, and the ultrasonic transceiver 2 is the receiving side.

  The transmission-side ultrasonic transceiver is connected to the transmission means 5, and the reception-side ultrasonic transceiver is connected to the subsequent reception circuit via two variable resistors 6.

  The receiving circuit includes a battery power supply 7 for supplying circuit driving power, a power switch 8 for switching power supply and stop of the power supply 7, an amplifying means 9 for amplifying the output of the receiving side ultrasonic transceiver, and an output from the amplifying means 9 It is comprised with the reception determination means 10 which detects reception of a sound wave signal.

  The variable resistor 6 is a volume resistor having a double structure, and is configured so that both have the same value in conjunction with each other.

  The trigger unit 11 outputs a trigger signal instructing the start of a series of measurement operations, and the timer 12 starts measuring the elapsed time after starting the ultrasonic measurement in synchronization with the trigger signal.

  The measurement value of the timer 12 when the reception determination means 10 determines the propagation of the received wave is the propagation time of this measurement.

  This propagation time is output to the calculation means 13, where various values related to flow measurement such as flow velocity and flow rate value are calculated.

  Here, one of the calculated values is an average value of propagation times for a predetermined number of times (for example, 8 times). This value is stored in the propagation time prediction means 14.

  The reception control means 15 controls the switching timing of the power switch and the resistance value of the variable resistor 6. The control timing at this time is based on the past measurement results stored in the propagation time prediction means 14. To be determined.

  The operation of the fluid flow measuring apparatus configured as described above will be described.

  First, the operation when the ultrasonic transmitter / receiver 2 is set as the transmission side will be described. First, a trigger signal instructing the start of measurement is output from the trigger means 11. At this time, the contact a of the transmission / reception switching means 4 is closed, and as a result, the ultrasonic transceiver 2 and the transmission means 5 are connected. The subsequent receiving circuit is connected via the ultrasonic transmitter / receiver 3 and the variable resistor 6.

  The variable resistance value at this time is set to a value (for example, 300Ω) that is substantially the same as the impedance of the reception-side ultrasonic transceiver.

  Furthermore, the contact of the power switch 8 is open, and the power supply to the receiving circuit is stopped.

In synchronization with the output of the trigger signal output from the trigger unit 11, a drive signal (for example, an AC signal of 500 kHz) is output from the transmission unit 5, and an ultrasonic signal is output from the vibration ultrasonic transmitter / receiver 2.

  In synchronization with this, the timer 12 starts and measurement of the elapsed time after the output of the ultrasonic signal starts.

  The ultrasonic signal output from the vibration ultrasonic transmitter / receiver 2 eventually reaches the receiving circuit, but its propagation time hardly changes unless the environmental conditions and flow rate change greatly. Therefore, the latest measured value is used. Predictable.

  By realizing a configuration in which power supply is started immediately before the propagation time based on the prediction data, it is possible to significantly reduce power consumption compared to the case where power is always supplied.

  The reception control means 15 obtains the first set time that is the switching timing of the power switch 8 and the second set time that is the resistance value switching timing of the variable resistor 6 based on the data stored in the propagation time prediction means 14. The switching signal is output at those times.

  As these setting time optimization methods will be described later, first, operations in the first and second setting times will be described first.

  When the measured value of the timer 12 started from the trigger signal output reaches the first set time, a control signal is output from the reception control means 15, the contact of the power switch 8 is closed, and the amplification means 9 and the reception from the power supply 7 are closed. Driving power is supplied to the determination means 10.

  At this time, due to the discontinuous voltage change that occurs, a slight potential difference is transiently generated between both terminals of the ultrasonic transceiver 3 on the receiving side. This potential difference becomes an energy source of unnecessary vibration of the reception-side ultrasonic transceiver 3.

  However, since this energy is not continuously supplied, it is consumed by the load resistance of the receiving circuit and eventually disappears.

  At this time, the consumption of vibration energy is faster when the resistance value of the receiving circuit is larger. At the moment when the power is turned on, since the connection resistance value of the ultrasonic transmitter / receiver 3 on the receiving side and the amplifying means 9 is set to the same value as the impedance of the transmitter / receiver 3, the transmitter / receiver and the load resistance are matched. Therefore, vibration energy can be consumed most efficiently.

  In addition, since the variable resistor 6 is used, even if the impedance differs for each receiving transducer due to individual variations, or even when using an ultrasonic transducer that has completely different characteristics for each model, the receiving side An optimum value can be set for the connection resistance value between the ultrasonic transceiver and the amplification means each time.

  When the measured value of the timer 12 reaches the second set time after the vibration energy is consumed, a control signal is output from the reception control means 10 to switch the resistance value of the variable resistor 6 to zero.

  After the second set time, when the ultrasonic signal propagated in the flow path reaches the ultrasonic transmitter / receiver 3, the signal output is output to the amplifying means 9 via the variable resistor 6. Since the connection resistance is switched to zero, the received signal voltage at both ends of the ultrasonic transceiver 3 can be transmitted to the amplifying means 9 with high efficiency.

The reception signal amplified by the amplifying unit 9 is output to the reception determining unit 10 where reception determination processing is performed. Although details of the reception determination means 10 are omitted, here, a specific part of the reception waveform is determined as a reception point, and specifically, a reception point determination is made on the falling edge of the zero-cross point in the third period of the reception waveform. And

  When reception determination is made by the reception determination means 10, the time measurement of ultrasonic propagation in the forward direction of the flow with the ultrasonic transmitter / receiver 2 as the transmission side and the ultrasonic transmitter / receiver 3 as the reception side ends.

  At the end of measurement in the forward direction, the measurement value of the timer 12 is output to the computing means 13 as the propagation time in the forward direction of the flow. At the same time, a control signal for switching transmission / reception is output from the reception control means 15.

  Upon receiving this control signal, the contact b of the transmission / reception switching means 4 is closed, the ultrasonic transmitter / receiver 3 and the transmitting means 5 are connected, the ultrasonic transmitter / receiver 2 and the receiving circuit are connected, and the transmission / reception relationship is reversed. To do. Further, the contact of the power switch 8 is opened, and the power supply from the power source 7 to the amplifying unit 9 and the reception determining unit 10 is stopped.

  The reception control unit 15 outputs a reset signal to the trigger unit 11 after a predetermined delay. The trigger unit 11 receives the reset signal and outputs a trigger signal for starting measurement to the timer 12 and the transmission unit 5.

  From here, measurement with the ultrasonic transmitter / receiver 3 as the transmission side is started. In the subsequent operation, a series of processes up to the reception determination in the reception determination means 10 is executed in the same manner as the procedure described above only by changing the transmission / reception relationship between the two transceivers.

  When reception determination is performed by the reception determination means 10, the time measurement of ultrasonic propagation in the direction opposite to the flow is completed with the ultrasonic transmitter / receiver 3 as the transmission side and the ultrasonic transmitter / receiver 2 as the reception side.

  At the end of the measurement in the reverse direction of the flow, the measurement value of the timer 12 is output to the calculation means 13 as the propagation time in the reverse direction of the flow. At the same time, a control signal for switching transmission / reception is output from the reception control means 15.

  In response to this control signal, the contact a of the transmission / reception switching means 4 is closed, the ultrasonic transceiver 2 and the transmission means 5 are connected, the ultrasonic transceiver 3 and the reception circuit are connected, and the transmission / reception of both transceivers is performed. The relationship is reversed again. Further, the contact of the first switch 12 is opened, and the power supply from the power source 7 to the amplifying unit 9 and the reception determining unit 10 is stopped.

  The reception control unit 15 outputs a reset signal to the trigger unit 11 after a predetermined delay, and this time, measurement using the ultrasonic transceiver 2 as a transmission side is started.

  As described above, every time measurement is performed, the measurement is continued while switching the transmission / reception relationship between the two ultrasonic transmitters / receivers while setting a certain delay time.

  When the predetermined number of times (e.g., 8 times in the forward direction and 8 times in the reverse direction) is completed, the calculation means 13 determines the average value of the propagation times separately for each of the forward direction and the reverse direction. , And the value is stored in the propagation time prediction means 14. Further, a flow rate value is obtained based on the average propagation time value.

  Next, a method for optimizing the first set time and the second set time using the propagation time average value stored in the propagation time predicting means 14 will be described.

  The value of the propagation time does not change abruptly in a short time unless a foreign gas is mixed in the flow path or the gas is intentionally replaced. Can be considered as an approximate expected value for the next eight measurements.

  Assuming that the forward propagation time average value of the flow is Ta, in the next eight forward measurements, vibration noise generated at both ends of the vibrator related to the first set time and the second set time is measured. Each control timing may be set in anticipation of an appropriate margin so as to be sufficiently small in the vicinity of the elapsed time Ta after the start.

  If the time until the vibration level converges after closing the power switch 8 is α, and the resistance value of the variable resistor 6 is switched to zero and the time until the vibration level converges is β, the value of the timer 12 The time when the elapsed time from the start of measurement shown in FIG. 4 becomes Ta− (α + β) is the first set time T1, and the time when the elapsed time becomes Ta−β is the second set time T2, and the variable resistance of the power switch 8 6 may be switched.

  As described above, in the fluid flow measurement device according to the present embodiment, based on the predicted propagation time stored in the propagation time prediction unit 14, the reception-side ultrasonic transceiver and the amplification unit 9 immediately before that time. The power of the amplifying means 9 is turned on in the state where the connection resistance is equal to that of the transmitter / receiver, and the vibration noise between the reception side ultrasonic transmitter / receiver generated at the time of power supply is rapidly attenuated. After that, since the ultrasonic signal is received after switching the connection resistance between the receiving-side ultrasonic transceiver and the amplifying unit 9 to zero, the power supply start timing of the amplifying unit 9 can be made closer to the received waveform. Therefore, high-precision measurement is possible while maintaining power saving performance.

  In addition, by setting the power-on timing separately in the forward and reverse directions of the flow, it is possible to set the optimal control timing regardless of flow rate fluctuations, enabling more accurate flow measurement while maintaining power saving performance. It becomes.

(Embodiment 2)
FIG. 2 shows the second embodiment, and the same reference numerals are given to the components that perform the same operations as those in FIG. 1, and the details of the first embodiment are used.

  The temperature detecting means 16 estimates the temperature of the fluid from the forward propagation time and the reverse propagation time obtained by the computing means 13. The reception control means 15 changes the first set time and the second set time according to the temperature estimated here.

  It is well known that the temperature of a gas and the speed of sound propagating in the gas are given by a first-order approximation.

  Therefore, if the distance between the ultrasonic transceivers and the gas type are known, it is possible to easily obtain the sound speed using the measured propagation time.

  This utilizes the fact that the sum of forward propagation time and reverse propagation time hardly changes even when the flow velocity changes.

  According to this property, it can be concluded that the average value of the two propagation times does not change under the same temperature condition. In other words, it can be said that the temperature can be known from the average value of the propagation time.

  In general, the impedance of the receiving-side ultrasonic transmitter / receiver changes slightly depending on the temperature. If the temperature is known as described above, the temperature characteristic is corrected and the resistance value on the high resistance side of the variable resistor 6 is changed. Just do it.

  As described above, in the embodiment of the present invention, the resistance value at the start of power supply of the amplifying unit 9 is controlled according to the estimated temperature in the apparatus estimated by the temperature estimating unit 16. Depending on the characteristics, it is possible to optimize the connection resistance between the reception-side ultrasonic transceiver and the amplification means.

  As described above, the fluid flow measuring device according to the present invention can bring the power-on timing of the amplifying means closer to the reception timing of the ultrasonic signal, and can save power. It can be applied to gas meters, water meters and the like.

1 is a block diagram of a fluid flow measurement device according to Embodiment 1 of the present invention. Block diagram of fluid flow measurement apparatus in embodiment 2 of the present invention Block diagram of a conventional fluid flow measurement device

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Fluid flow path 2,3 Ultrasonic transmitter / receiver 4 Transmission / reception switching means 6 Variable resistance 7 Power supply 8 Power switch 9 Amplification means 10 Reception determination means 12 Timer 13 Calculation means 14 Propagation time prediction means 15 Reception control means 16 Temperature estimation means 17 Impedance Estimating means

Claims (3)

At least a pair of ultrasonic transmitters / receivers disposed on the upstream side and downstream side of the fluid flow path, amplification means connected to the one ultrasonic transmitter / receiver set on the receiving side via a load resistor, and A power switch for switching the supply / stop of power to the amplification means, a resistance value switching means for switching the connection resistance value of the one ultrasonic transmitter / receiver set on the receiving side and the amplification means, and an output of the amplification means A reception determination means for determining reception of an ultrasonic signal based on the above, a timer for measuring a propagation time from transmission to reception of the ultrasonic signal, and a next predicted propagation based on a past propagation time measured by the timer A propagation time predicting means for determining a time; and a reception control means for controlling the power switch and the resistance switching means. The reception control means includes a first setting prior to the predicted propagation time. Power supply to the amplifying means is started by the power switch at a time, and the ultrasonic wave transceiver and the ultrasonic transmitter / receiver by the resistance value switching means at a second set time between the first set time and the predicted propagation time A fluid flow measuring device characterized in that the connection resistance with the amplifying means is switched from a high resistance value equivalent to the impedance of the one ultrasonic transmitter / receiver set on the receiving / receiving side to a low resistance value which can be regarded as almost zero. . By switching the roles of the transmitting-side ultrasonic transmitter / receiver and the receiving-side ultrasonic transmitter / receiver, transmission / reception switching means that enables measurement in both the forward and reverse directions of the flow, and the fluid based on the propagation time measured by the timer Calculating means for calculating the flow velocity and / or flow rate, wherein the reception control means determines the first and second set times based on the individual predicted propagation times in the forward direction and the reverse direction of the flow. The fluid flow measuring device according to claim 1. Temperature estimation means for estimating the ambient temperature of the apparatus based on the measured propagation time, and impedance estimation means for estimating the impedance of the reception-side ultrasonic transceiver according to the estimated temperature of the temperature estimation means, the reception control means, 3. The fluid flow measuring device according to claim 1, wherein a value on a high resistance side of a connection resistance between the reception-side ultrasonic transceiver and the amplification unit is controlled in accordance with an output of the impedance estimation unit.

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