JP4835068B2 - Fluid flow measuring device - Google Patents

Description

  The present invention relates to a fluid flow measurement device that detects the flow velocity of a fluid by measuring the propagation time of an ultrasonic signal and measures the flow rate of the fluid as necessary.

  Conventionally, this type of flow measurement device has been proposed using a technique called a sing-around method that increases measurement resolution by repeating transmission and reception between two vibrators a plurality of times (see, for example, Patent Document 1). ).

  FIG. 8 is a block diagram of a flow rate measuring apparatus using the sing-around method. A first vibrator 32 that transmits ultrasonic waves and a second vibrator 33 that receives the transmitted ultrasonic waves are disposed in the flow direction in the middle of the fluid conduit 31, and the pair of vibrators 32 and 33. And a control unit 35 for controlling the measurement unit 34, and a calculation unit 36 for determining the flow velocity and / or flow rate of the fluid based on the measurement result of the measurement unit 34. Has been.

  Here, the sound velocity is C, the flow velocity is v, the distance between the pair of transducers 32 and 33 is L, and the angle between the ultrasonic wave propagation direction and the flow direction is θ, and is arranged upstream of the fluid conduit 31. When the ultrasonic wave is transmitted from the first vibrator 32 and received by the second vibrator 33 disposed on the downstream side, the propagation time is t1, and the reverse propagation time is t2, t1 and t2 are It can be obtained by an expression.

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

v = L · (1 / t1−1 / t2) / 2 cos θ (Formula 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 conduit 31.

  By the way, in (Equation 3), the term in parentheses can be transformed as in (Equation 4).

(T2-t1) / t1 · t2 (Formula 4)
Here, the denominator term in (Equation 4) has a substantially constant value regardless of the change in flow velocity, whereas the numerator term has a value that is substantially proportional to the flow velocity. Therefore, it is necessary to accurately measure the difference between the two propagation times.

  For this reason, as the flow rate becomes slower, it is necessary to obtain a minute time difference, and in order to measure as a single phenomenon, the measurement unit 34 needs to have a very small time resolution on the order of nanoseconds, for example. It is difficult to realize such a time resolution, and even if it can be realized, power consumption is increased by increasing the time resolution.

As a result, the necessary time resolution is realized by repeatedly measuring the transmission of ultrasonic waves and obtaining the average value. That is, if the time resolution of the measurement unit 34 is TA and the number of repetitions is M, the measurement resolution of the propagation time can be set to TA / M by continuously operating the measurement unit 34 during this repeated measurement. it can. Therefore, high-resolution measurement can be realized without increasing power consumption.
JP 2000-310550 A

  However, since the conventional configuration is based on the premise of repeated continuous operation, the time required for a series of measurement operations becomes longer and current consumption increases. Therefore, in a system such as a home gas meter that requires battery-operated yearly operation guarantee, it is necessary to leave a certain period of pause after repeating measurement once in order to reduce current consumption as much as possible. there were.

  As a result, only local information of the fluid can be obtained, and there is a problem that followability is poor with respect to a variable flow repeated at a relatively short period.

  The present invention solves the above-described conventional problems, and an object of the present invention is to provide a fluid flow measurement device that can set a measurement interval freely and has high followability to changes in flow rate and the like.

  In order to solve the above-described conventional problems, the fluid flow measurement device according to the present invention is configured to detect a predetermined number of zero-cross points that are generated a plurality of times in succession by an ultrasonic signal, and a detection unit. It has time measuring means to measure the elapsed time to each zero cross point and time calculation means to find the propagation time by calculating the average value of the elapsed time obtained by the time measuring means, so only the number of detection times of zero cross points Since the measurement resolution of the time measuring means is increased and a high resolution can be realized without performing continuous repeated measurement, the degree of freedom of the measurement interval is increased and the followability to the flow rate change can be improved.

  The flow rate measuring apparatus of the present invention can realize high resolution without performing continuous repeated measurement.

According to a first aspect of the present invention, a first transducer that is provided in a fluid conduit and transmits an ultrasonic signal, a second transducer that receives an ultrasonic signal transmitted from the first transducer, and the second transducer Detecting means for detecting a predetermined number of zero-cross points that are generated a plurality of times in succession by the ultrasonic signal received at the time, and a zero-cross point that is activated from the start of transmission of the first transducer and detected by the detecting means Time measuring means for stopping after measuring each elapsed time, time calculating means for calculating a propagation time using an average value of values measured by the time measuring means, and measurement by the time measuring means are completed a predetermined number of times. Switching means for switching the transmission / reception roles of the first vibrator and the second vibrator every time, and calculation means for calculating the flow velocity and / or flow rate using the bidirectional propagation time obtained by the time calculation means. , The flow rate calculation As the flow rate obtained by the means increases, the number of zero cross points detected by the detecting means is reduced, so that the detecting means detects a predetermined number of zero cross points of the ultrasonic signal, and the time measuring means Since the propagation time is obtained by calculating the average value of the elapsed time from the measured transmission start to each zero cross point, the measurement resolution of the time measuring means is increased by the number of times of detection of the zero cross point, and continuous repetition Since high resolution can be realized without performing measurement, it is possible to freely set the measurement interval and improve followability with respect to flow velocity and / or flow rate change. Furthermore, as the flow rate obtained by the calculation means increases, the number of zero-cross points detected by the detection means is reduced, thereby reducing the operating time of the device at high flow rates and / or high flow rates. The current can be reduced.

  In the second invention, in particular, the time measuring means of the first invention is composed of a synchronous clock and a timer counter, and the oscillation period of the synchronous clock and the oscillation period of the ultrasonic signal are determined to be in a relatively prime relationship. Since the phase of the synchronous clock at the point is different every time, the measurement resolution can be more reliably increased.

In the third invention, the measurement can be performed without being affected by the reverberation or reflection of the ultrasonic signal by prohibiting the next measurement for a predetermined time after the measurement of the time measuring means of the first or second invention is completed. Therefore, measurement accuracy can be improved.

  According to the fourth aspect of the invention, in particular, as the flow velocity and / or flow rate obtained by the computing means of the first or second invention is reduced, the number of times of measurement until the switching means switches between transmission and reception is increased, so that the arithmetic processing is performed. Therefore, the power consumption can be reduced.

  According to the sixth aspect of the invention, it is possible to always measure the propagation time accurately by adding correction to the propagation time obtained by the time calculation means, particularly according to the number of zero cross points detected by the detection means of the fifth invention. As a result, measurement accuracy is improved.

  According to the seventh aspect of the invention, in particular, by setting the number of zero cross points detected by the detection means of the sixth invention to an even number, an accurate propagation time can be obtained regardless of the output characteristics of the detection means. As a result, measurement accuracy is improved.

  In the eighth aspect of the invention, in particular, the zero cross point detected by the detection means of the sixth aspect of the invention is limited to only the rising or falling edge of the AC signal, so that an accurate propagation time can be obtained regardless of the output characteristics of the detection means. As a result, the measurement accuracy is improved.

(Embodiment 1)
In FIG. 1, a first vibrator 2 that transmits ultrasonic waves is arranged in the middle of the fluid conduit 1 on the upstream side of the flow, and a second vibrator 3 that receives ultrasonic waves transmitted from the first vibrator 2 is provided. Located downstream of the flow.

  The first vibrator 2 and the second vibrator 3 are connected to a subsequent processing block through switching means 4 that reverses the role of transmission and reception. That is, by the action of the switching means 4, it is possible to make the first vibrator 2 the transmitting side and the second vibrator 3 the receiving side. The trigger means 5 outputs a trigger signal that instructs the start of measurement, and an ultrasonic drive signal is output from the transmission circuit 6 in synchronization with this signal.

  An output signal of the transmission circuit 6 is output to the first transducer 2 via the switching unit 4, and an ultrasonic signal is output from the first transducer 2. The ultrasonic signal transmitted from the first transducer 2 and received by the second transducer 3 is amplified by the amplification circuit 7 via the switching unit 4 and then output to the detection unit 8. The detection means 8 compares the size of the ultrasonic signal, which is an AC signal, with its zero point, determines that the point where the magnitude relationship is reversed is the zero cross point, and detects the zero cross point by a predetermined number. Stop the operation.

  And the elapsed time about each zero crossing point detected by the detection means 8 is measured by the time measuring means 9 which started measurement simultaneously with the output of the trigger means 5. The measurement result of the time measuring means 9 is once outputted to the storage means 10 and then outputted to the time calculating means 11 and converted into ultrasonic propagation time by performing necessary calculations.

  The time from the trigger signal output by the trigger means 5 to the stop of the time measuring means 9 is regarded as one measurement operation, and after one measurement operation is completed, an appropriate time interval (much longer than one propagation time). Then, a series of operations from the trigger signal output by the trigger unit 5 to the time measuring operation by the time measuring unit 9 is repeated intermittently.

Further, the propagation time obtained by the time calculator 11 is output to the integrating means 12. Integration means 12
Then, the integrated value of the propagation time is obtained. Each time the measurement by the time measuring means 9 is completed a predetermined number of times, the integrated value is output to the flow rate calculating means 13, and the switching means 4 transmits and receives the first vibrator 2 and the second vibrator 3. The role is changed, and the integrated value of the propagation time in the reverse direction (ultrasonic transmission from downstream to upstream of the flow) is calculated in the same procedure. Then, a flow rate value is obtained by the flow rate calculation means 12 based on a set of propagation times in the forward direction and the reverse direction.

  Further, the measurement control unit 14 controls the operation of the entire apparatus, and plays a role of instructing the trigger unit 4 at a measurement start timing and a role of instructing the switching unit 4 to change a transmission / reception role.

  FIG. 2 shows the time measuring means 9, and the synchronous clock generating means 15 is composed of a transmitter 16 that periodically generates a pulse signal and a control gate 17, and this control gate 17 is an output of the transmitter 16. In response to an external control signal, a synchronous clock is generated.

  The timer counter 18 counts rising edges of the synchronous clock output from the control gate 17. The control gate 17 is composed of an AND gate, and outputs the input signal input from the transmitter 16 as it is as a synchronous clock of the timer counter 18 when the control signal is “H” output.

  Therefore, the control signal is set to “H” at the start time of the measurement target, the control signal is set to “L” at the end time, and the number of synchronous clocks input to the timer counter 18 during this period is counted, thereby measuring the measurement target. It becomes possible to do.

  FIG. 3 shows the operation of the detection means 8 and the operation of the time measuring means 9, and the procedure for obtaining the propagation time from the value measured by the time measuring means 9 will be described. The detection means 8 is composed of an electronic circuit that compares the two threshold voltages VA and VB with the reception signal output from the amplifier circuit 7.

  First, the arrival of the ultrasonic signal is detected at time T0 when the received signal exceeds the threshold voltage VA, and the enable signal that validates the comparison process with the threshold voltage VB becomes “H”. Thereafter, as the output of the comparison means 8, “L” is output if the threshold voltage VB is large, and “H” is output if the received signal is large. The ultrasonic reception signal is an AC signal, and the threshold voltage VB is adjusted to be the zero point of this AC signal.

  As shown in FIG. 3, the output of the detection means 8 is inverted several times continuously. Here, let the elapsed time from the start of transmission to each inversion point be T1, T2,... T6 from the beginning. The time measuring means 9 outputs the value of the timer counter 17 at these inversion points to the storage means 10.

  When six predetermined zero-crossing points are detected, the enable signal becomes “L”. Thereafter, the comparison processing between the threshold voltage VB and the ultrasonic signal is completed, and the output of the detecting means 8 is maintained in the final state. Is done. In the time measuring means 9, when the value for six times which is a predetermined number of times is taken, the control signal output to the control gate 17 becomes “L”, the supply of the synchronous clock to the timer counter 18 is stopped, and the time measuring means 9 The operation ends.

  The six measurement values stored in the storage unit 10 are output to the time calculation unit 11, and the time calculation unit 11 obtains an average value of the six measurement values.

  Here, as long as the phase relationship between the oscillation cycle of the ultrasonic signal and the oscillation cycle of the synchronization clock of the time measuring means 9 does not completely overlap, the phase of the synchronization clock at the inversion timing of the output of the comparison means 8 is different every time. Thus, it is possible to identify a time change smaller than the oscillation period of the synchronous clock.

  If the oscillation period of the synchronous clock is Ts and the number of inversion inputs is N, the average resolution of the N measured values obtained by the time measuring means 9 is obtained, so that the apparent resolution of the time measuring means is averaged by Ts / N will be raised.

  In particular, by setting the transmission cycle of the ultrasonic signal and the transmission cycle of the synchronous clock to be relatively prime, that is, the ratio between the two does not become a value near the integer value, the phase shift for each detection point is ensured. Become. Therefore, by setting N to an appropriate number, the time resolution can be increased by one operation of the time measuring means 9.

  As described above, according to the first embodiment, the detection means detects a predetermined number of zero cross points of the ultrasonic signal, and the time measuring means measures the elapsed time from the start of transmission to each zero cross point. Since the propagation time is obtained by obtaining the average value by the computing means 11, the measurement resolution of the time measuring means is increased by the number of times of detection of the zero cross point, and continuous transmission and reception is performed as in the thin ground method. Therefore, intermittent measurement can be performed, and the measurement processing interval can be freely set. As a result, it is possible to provide a flow measurement device having high followability to a change in flow velocity and / or flow rate.

  In addition, when the next measurement is performed after the measurement by the time measuring means 9, if an appropriate forbidden time, that is, a measurement prohibited time is provided, it is not affected by reverberation or reflection of the previous ultrasonic signal. In addition, accurate measurement is possible. In this case, since the control signal for the control gate 17 is “L” while the re-measurement is prohibited, no synchronization clock is input to the timer counter 18 no matter how long the forbidden time becomes. Therefore, extra power consumption can be reduced.

(Embodiment 2)
FIG. 4 is a characteristic diagram for explaining the operation of the second embodiment of the present invention. FIG. 4 shows the relationship between the measured flow rate and the number of measurements until the switching unit 4 switches between transmission and reception of the two vibrators. That is, based on the previous measured flow rate, the next measured flow rate is estimated, and the frequency at which the switching means 4 is operated is determined. As shown in the figure, as the flow rate decreases, the set number of times required for transmission / reception switching is increased. Since the flow rate calculation means 13 obtains the flow rate as a pair of two values with different transmission directions of the accumulated value of the propagation time obtained by the accumulation means 12, each time the measured flow rate becomes smaller, the processing time becomes longer. The frequency of the flow rate calculation that causes the increase is reduced, and as a result, the current consumption is reduced. In particular, in a device such as a home gas meter that requires a long operation time of 10 years without battery replacement, the implementation effect is great.

(Embodiment 3)
FIG. 5 shows, for example, the measured flow rate and the number of zero cross points detected by the detection means 8. The measured flow rate on the horizontal axis indicates the measured flow rate one time before. In other words, the next measured flow rate is estimated based on the previous measured flow rate, and the number of zero cross points detected by the detection means 8 is changed.

As shown in the figure, in the region where the flow rate is less than Q ₁ [L / h], the number of detection points is 6, and hereinafter, the number of detection points decreases step by step as the flow rate increases. In the area above Q ₅ [L / h], the number of measurement points is one.

  According to this configuration, the number of measurement points is increased at a small flow rate that requires fine resolution, and conversely, the measurement point is decreased at a large flow rate that has little influence even if the resolution is rough. Thus, when the flow rate is small with a small number of measurement points, the operation time of the electronic circuit is reduced, and the current consumption of the entire apparatus is not wasted.

In particular, in a device such as a home gas meter that requires a long operation time of 10 years without battery replacement, the implementation effect is great.

  Next, how to determine the propagation time will be described with reference to FIG. In FIG. 6, a waveform A is an example of an output waveform of the detection means 8 when the flow rate is less than Q1, and a waveform B is an example of an output waveform when the flow rate is Q5 or more. Although both waveforms are originally different in time absolute value by different flow speeds, they are displayed with the same time axis for simplicity.

  First, in the case of the waveform A, since the number of detection points is 6, the time measuring means 9 measures TA1 to TA6 and the average value is obtained by the time calculating means 10. At this time, the obtained average value is the time at the midpoint of TA3 and TA4, that is, the time at the midpoint of the third and fourth zero cross points. On the other hand, in the case of the waveform B, since the time measuring means 9 measures only TB1, the average value is also TB1, and the time of the first zero cross point is obtained.

  Therefore, in this state, the detection points of both are displaced. Since one point of the zero cross point is equal to 0.5 period of the ultrasonic signal, the time difference between them is 1.25 period.

  Therefore, by subtracting 1.25 cycles of the ultrasonic signal from the average value from TA1 to TA6, the time of the first zero cross point can be obtained for both waveforms A and B.

  FIG. 7 shows the relationship between the number of zero cross points detected by the detection means 8 and the calculation correction amount ΔT in the time calculation means 11.

  In FIG. 7, the horizontal axis represents the number of zero cross points, and the vertical axis represents the ratio ΔT / TW between the correction amount ΔT and the period TW of the ultrasonic signal. As shown in the figure, when the number of detection points is one, the correction amount is 0, and thereafter, every time the number of detection points increases, correction for 0.25 period may be applied.

  If the correction amount ΔT obtained in this way is subtracted from the average value obtained by the time calculation means 11, the time of the first zero cross point can always be obtained regardless of the number of zero cross points detected by the detection means 8. become.

  The above calculation is valid when the duty of the output waveform of the detection means 8 is 50% no. However, the duty is not necessarily 50% when the threshold value VB of the detection means 8 deviates from the zero point of the AC signal or due to the influence of the offset of the circuit. When the duty deviates from 50%, a slight error occurs in the above correction method. Therefore, if the number of detection points is limited to an even number in order to perform more accurate correction, accurate correction can be realized regardless of the duty of the output signal of the detection means 8.

  The same effect can be obtained even if the number of detection points is limited to only the rise or fall of the output of the detection means 8.

  Since the flow rate measuring device of the present invention can freely set the measurement interval, it can be applied, for example, under conditions where pulsating flow is always generated.

The block diagram of the flow measurement apparatus in Embodiment 1 of this invention The block diagram of the time measuring means in Embodiment 1 of this invention Timing chart for explaining the operation of the time measuring means in Embodiment 1 of the present invention FIG. 6 is a characteristic diagram for explaining the operation of the flow measuring apparatus according to the second embodiment of the present invention. FIG. 6 is a characteristic diagram for explaining the operation of the flow measuring apparatus according to the third embodiment of the present invention. Timing chart for explaining the operation of the timing means in Embodiment 3 of the present invention Correction characteristic diagram of time calculation means in Embodiment 3 of the present invention Block diagram of a conventional flow measurement device

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Fluid pipe line 2 1st vibrator | oscillator 3 2nd vibrator | oscillator 4 Switching means 8 Detection means 9 Time measuring means 11 Time calculating means 13 Flow rate calculating means 15 Synchronous clock generating means 18 Timer counter

Claims (7)

A first transducer that is provided in the fluid conduit and transmits an ultrasonic signal;
A second transducer for receiving an ultrasonic signal transmitted from the first transducer;
Detecting means for detecting a predetermined number of zero-cross points that are continuously generated a plurality of times by the ultrasonic signal received by the second vibrator;
Timing means that starts from the start of transmission of the first oscillator and stops after measuring the elapsed time of each zero cross point detected by the detection means;
Time calculating means for calculating a propagation time using an average value of values measured by the time measuring means;
Switching means for switching the transmission / reception roles of the first vibrator and the second vibrator every time the measurement by the time measuring means is completed a predetermined number of times;
Calculating means for calculating the flow velocity and / or flow rate using the bidirectional propagation time obtained by the time calculating means ,
A fluid flow measurement device that reduces the number of zero-cross points detected by the detection means as the flow rate obtained by the flow rate calculation means increases . The clock means is constituted by a synchronous clock and timer counter, the synchronization clock of the fluid flow measuring device according to claim 1, wherein the oscillation period defined disjoint relationship oscillation period and the ultrasound signal. The fluid flow measuring device according to claim 1 or 2, wherein after the measurement by the time measuring means is completed, the next measurement is prohibited for a predetermined time. The flow rate in accordance with the flow rate determined is reduced by the operation means, the fluid flow measuring apparatus according to claim 1 or 2, wherein the switching means is set larger the number of measurements to switch between transmission and reception. In response to said number of zero-cross points detected by the detecting means, the fluid flow measuring device according to any one of the time calculating claims propagation time calculated by the unit and to add a correction 1-4. 6. The fluid flow measuring device according to claim 5 , wherein the number of zero cross points detected by the detecting means is set to an even number. 6. The fluid flow measuring device according to claim 5 , wherein the zero cross point detected by the detecting means is limited to only one of rising and falling of the AC signal.

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