JP2006214793A - Device for measuring flow rate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a device for measuring a flow rate having high following property even under a condition having strong flow rate variation. <P>SOLUTION: A delay generating means 9 slightly delays the transmission start timing of a first oscillator 2 from a measurement start timing of a time measuring means 7. The propagation time is sequentially determined by a measurement control means 11 while the setting of the delay time is changed with a resolution smaller than the time measuring resolution of the time measuring means 7. Therefore, the time can be read with a resolution further smaller than the time measuring resolution of the time measuring means 7, and continuous repeating measurement is not required. Therefore, the degree of freedom of measurement interval increases, and flow rate measurement having high following property to the flow rate variation is allowed. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

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

  Conventionally, this type of flowmeter 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 (for example, see Patent Document 1). .

  FIG. 6 is a block diagram of a flow rate measuring apparatus using the sing-around method. As shown in FIG. 6, a first vibrator 32 that transmits ultrasonic waves and a second vibrator 33 that receives the transmitted ultrasonic waves are arranged in the flow direction in the middle of the fluid conduit 31, and transmit. A measurement unit 34 that measures the propagation time of ultrasonic waves using two vibrators 32 and 33, a control unit 35 that controls the measurement unit 34, and a measurement result of the measurement unit 34. And a calculation unit 36 for calculating the fluid flow rate.

In FIG. 6, the sound velocity is C, the flow velocity is v, the distance between the two vibrators 32 and 33 is L, the angle formed by the propagation direction of the ultrasonic wave and the flow direction is θ, and upstream of the fluid conduit 31. When the ultrasonic wave is transmitted from the arranged first vibrator 32 and received by the second vibrator 33 arranged on the downstream side, the propagation time is t ₁ , and the propagation time in the reverse direction is t ₂ , t ₁ and t ₂ can be obtained by the following expression.

t ₁ = L / (C + v cos θ) (Formula 1)
t ₂ = 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 / t ₁ −1 / t ₂ ) / 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).

(T ₂ −t ₁ ) / t ₁ t ₂ (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 of 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. Therefore, the necessary time resolution is realized by repeatedly measuring the transmission of the ultrasonic wave many times and obtaining the average value. That is, if the time resolution of the measurement unit 34 is T _A and the number of repetitions is M, the measurement resolution of the propagation time is T _A / M by operating the measurement unit 34 continuously during this repeated measurement. be able to. 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 the current consumption increases. Therefore, in a system that requires battery-driven yearly operation guarantees, such as a home gas meter, it is necessary to leave a certain period of pause after repeating measurement once to minimize current consumption. there were. Therefore, since only local information on the fluid can be obtained, there is a problem that followability is poor with respect to a variable flow that is repeated in a relatively short period.

  The present invention solves the above-described conventional problems, and an object of the present invention is to provide a flow rate measuring apparatus that freely sets a measurement interval and has high followability to a flow rate change.

  In order to solve the above-described conventional problems, the fluid flow rate measuring device of the present invention includes delay generation means for generating a minute time difference between the measurement start or measurement end of the time measurement means and the timing of transmission and reception, and the delay generation means The delay time can be changed by a predetermined range with a resolution smaller than the timekeeping resolution of the timekeeping means, so high resolution can be realized without performing continuous repeated measurement, increasing the degree of freedom of measurement intervals and responding to changes in flow rate 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, there is provided 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 transducer. Timekeeping means that starts and stops each time an ultrasonic wave propagates and measures the propagation time, switching means that reverses the transmission / reception direction of the vibrator every time the measurement by the timekeeping means reaches a predetermined number of times, and measurement by the timekeeping means A delay generating means for generating a minute time difference between the start or end of measurement and transmission / reception timing; a measurement control means for controlling the delay generating means and the switching means; and a measured value of the time measuring means and the delay time. A flow rate calculation means for obtaining a flow rate based on the delay time, and the measurement control means can change the delay time of the delay generation means by a predetermined range with a resolution smaller than the timekeeping resolution of the timekeeping means. By measuring while changing sequentially, a time resolution smaller than the time resolution of the time measuring means can be obtained, so high resolution can be realized without performing continuous repeated measurement, so the measurement interval can be set freely and the flow rate change The followability can be improved.

  In the second invention, in particular, the measurement control means of the first invention measures the delay time resolution while sequentially changing the delay time resolution by setting the delay time setting range to an integral multiple of the timekeeping resolution of the timekeeping means. It becomes possible to obtain a resolution obtained by finely and evenly dividing the time resolution of the time measuring means.

  In the third aspect of the invention, in particular, the measurement control means of the first aspect of the invention prohibits the next measurement for a predetermined time after the measurement by the time measurement means, thereby preventing the influence of the reverberation or reflection of the ultrasonic signal. Measurement accuracy can be improved.

  In the fourth aspect of the invention, in particular, the measurement control means of the second aspect of the invention switches transmission / reception every time the set value of the delay means circulates an integer number of times, and the flow rate calculation means obtains the flow rate by measuring one pair of transmission / reception switching. As a result, the resolution of the required flow rate value can be increased.

  In the fifth aspect of the invention, the flow rate can be obtained with high accuracy due to the averaging effect even at the time of a small flow rate where the flow rate is not stable, particularly by determining the number of circulations as the measured flow rate becomes smaller in the fourth aspect of the invention. .

  According to a sixth aspect of the invention, in particular, the timing means of the fourth aspect of the invention comprises a synchronous clock generation means and a timer counter, and the measurement control means increases the oscillation cycle of the synchronous clock as the measurement flow rate decreases, and delays By setting the time setting resolution to ½ or less of the minimum oscillation period of the synchronous clock, power consumption can be reduced without impairing the measurement resolution when the flow rate is small, so that the power consumption of the entire apparatus can be reduced.

(Embodiment 1)
FIG. 1 is a block diagram of a flow meter side device according to the first embodiment of the present invention.

  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 transmission circuit 4 outputs a transmission signal to the first vibrator 2, and the reception signal received by the second vibrator 3 is amplified by the amplification circuit 5 and then compared with the reference signal by the comparison circuit 6. The time until reception is obtained by the time measuring means 7. The trigger unit 8 instructs the time measuring unit 7 to start timing at regular intervals, and at the same time, the delay generating unit 9 generates a minute delay time, and after the delay time ends, an ultrasonic drive signal is transmitted from the transmission circuit 4. The first vibrator 2 and the second vibrator 3 can reverse the direction of transmission and reception by the action of the switching means 10. That is, when an inverted signal of transmission / reception is output from the switching means 10, the transmission circuit 4, the second vibrator 3, and the amplification circuit 5 are arranged so that the second vibrator becomes the transmission side and the first vibrator becomes the reception side. The first vibrators 3 are connected to each other. The measurement control unit 11 controls the switching timing of the switching unit 10 and the measurement operation including the delay generation unit 9. Based on the propagation time obtained by the time measuring means 7, the flow rate calculating means 12 obtains the flow rate value in consideration of the size of the pipe line and the flow state.

  FIG. 2 is a block diagram of the time measuring means 7. The synchronous clock generating means 13 is composed of a transmitter 14 that periodically generates a pulse signal and a control gate 15. The control gate 15 receives the output of the transmitter 14 and a control signal from the outside. , Generate a synchronous clock. The timer counter 16 counts the rising edge of the synchronous clock output from the control gate 15 and the value is added to the adder 17.

  The control gate 15 is composed of an AND gate, and outputs the input signal input from the transmitter 14 as it is as a synchronous clock of the timer counter 16 when the control signal is “H” output. Accordingly, the control signal is set to “H” at the start time of the measurement target, and the control signal is set to “L” at the end time. By counting the number of synchronous clocks input to the timer counter 16 during this time, the measurement target is timed. It becomes possible to do.

Next, a method for measuring the propagation time will be described. At the same time as the trigger signal is output from the trigger means 8, the control signal of the control gate 15 changes from "L" to "H". As a result, a synchronous clock is input from the control gate 15 to the timer counter 16 at regular intervals, and the propagation time is started. After the timing of the start of counting of the small delay time T _D, the transmission output from the transmission circuit 4. Then, the delay time T _D is a variable, the set resolution T _S is clocked resolution measuring unit 7, namely, is defined from the oscillation period T _C of a synchronous clock to a value 1 / 3T _C. First, the delay time at the first transmission _{T D1} is 1 / 3T _C, thereafter, the second delay time _{T D2} is 2 / _3T C, 3-time delay time _{T D3} is a _{T C,} the delay time T _D is set resolution _{T S,} i.e. gradually varied by 1 / 3T _C. By slightly changing the T _D, because the synchronous clock phase at the measurement point is different every time, it is possible to read a short time change of less than one cycle of the synchronous clock. Then, in particular, the T _D reaches an integral multiple of the synchronous clock, it is possible to obtain a resolution which is equally divided into an integer fraction of the synchronization clock.

This resolution improvement effect will be described with reference to FIGS. FIG. 3 shows timer counter values when there is no delay time and when the delay times are T _D1 , T _D2 , and T _D3 . The count values in each case are N, N + 1, N + 1, and N + 1. N + 1, N + 1, and N + 1, which are values counted from the first transmission to the third transmission / reception, are added by the adder 17, and the added value 3N + 3 is output to the flow rate calculation means 12.

In the flow rate calculation means 12, a process for correcting the delay time is performed on the value obtained by the adder 17. Three delay time _{1 / 3T C, 2 / 3T} C, since the sum from _{T C} is determined to 2T _C, average of three propagation time can be calculated by the following equation.

Tave = {(3N + 3) × T C -2T C} / 3 = (N + 1/3) · T C ( Equation 5)
FIG. 4 shows the relationship between the propagation time and the measured value when read by this method, using the value of the timer counter 16. According to FIG. 4, it can be seen that the time resolution is 1/3 of the counter value, and the time change can be read with a resolution of 1/3 when there is no delay.

The time resolution obtained by the method as described above is the time resolution of the time measuring means 7, that is, the period T _{C of the} synchronous clock, the delay time setting resolution T _S , and the difference T _C -T _S between the two resolutions. Can be defined as the smallest value. In the example above, each of three _values, because the _{T C, 1 / 3T C,} 2 / 3T C, the time resolution is 1 / 3T _C. The setting range of delay time T _D is not limited to an integral multiple of the time resolution T _C as previously described, if the value of the integral multiple proximity, timing resolution T _C almost equally divided Resolution can be obtained. Further, even if a value out of the integer multiples, the average resolution, it is needless to say that a value smaller than the resolution T _C obtained by clocking means 7 alone.

  The same resolution can be obtained regardless of the transmission interval. Therefore, unlike the case of assuming a continuous operation as in the sing-around method, it is possible to freely set the transmission interval of the ultrasonic waves, and the followability to the flow rate change can be improved.

  If the transmission interval is short, the reverberation or reflected wave of the previously transmitted ultrasonic wave may be adversely affected by the measurement accuracy by combining it with the subsequent transmission wave. If the configuration is such that re-measurement is prohibited for a predetermined time, that is, the time until the influence of reflection and reverberation is eliminated, highly accurate measurement can be realized. In this case, since the control signal for the control gate 15 is “L” while the remeasurement is prohibited, the synchronization clock is not input to the timer counter 16, and therefore, excessive power consumption can be reduced.

  Next, a flow rate calculation method will be described. Since the setting is completed by changing the set value of the delay time three times, at this time, the measurement control unit 11 reverses the direction of transmission / reception of the transducer by the switching unit 10 and receives the first transducer 2. In the same manner, three measurements are performed with the second vibrator 1 as the transmitting side. Therefore, since it is possible to measure the propagation time with high resolution in both directions, the flow rate value can be obtained with high accuracy as well.

  Note that the flow rate calculation timing is not limited to each set cycle, and may be after two or three cycles. In particular, when the flow rate is small, the flow rate itself is often unstable. Therefore, if the flow rate is obtained after a plurality of circulations, an accurate value can be obtained by averaging.

  In addition, it is not related to the configuration in which the flow rate calculation is performed every set round or integer rounds, and it can be easily estimated that the total integrated flow rate value can be obtained with the same accuracy even when the switching timing is different. .

  In the present embodiment, the transmission of the ultrasonic wave is delayed from the start of time measurement by the time measuring means 7, but conversely, the time start of the time measuring means 7 is delayed or the measurement end of the timer is terminated. It goes without saying that the same effect can be obtained even with a delayed configuration.

(Embodiment 2)
FIG. 5 is a block diagram of the time measuring means 7 in the second embodiment. FIG. 5 differs from FIG. 2 in that the clock pulse output from the transmitter 14 is output to the control gate 15 after passing through the frequency divider 18.

As shown in the first embodiment, the time resolution includes the time resolution of the time measuring means, that is, the period T _{C of the} synchronization clock, the delay time setting resolution T _S , and the difference T _C -T _S between the two resolutions. Can be defined as the smallest value. If the transmission frequency of the transmitter 14 before passing through the frequency divider 18 is T _C and T _S is set to be smaller than ½ of T _C , the synchronous clock cycle output to the control gate 14 by the frequency divider 17 is set. even if just how large, resolution is always T _S. Therefore, the current consumption of the timer counter 16 can be reduced without degrading the resolution. Therefore, if the synchronous clock period input to the timer counter 16 through the frequency divider 18 circuit is set to be long when the amount of fluid used is small, the total current consumption of the entire apparatus can be reduced. In particular, when applied to a home gas meter, it is required to operate for many years without replacing the battery for a long time. Considering the actual usage, the time when the gas is not used is overwhelmingly long, so it can be said that the effect of reducing power consumption is extremely high when the flow rate is small.

  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.

Block diagram of a flow rate measuring device in Embodiment 1 of the present 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 The characteristic figure which shows the time resolution of the time measuring means in Embodiment 1 of this invention The block diagram of the time measuring means in Embodiment 2 of this invention Block diagram of a conventional flow measurement device

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Fluid line 2 1st vibrator 3 2nd vibrator 7 Time measuring means 9 Delay generating means 10 Switching means 11 Measurement control means 12 Flow rate calculating means 13 Synchronous clock generating means 16 Timer counter

Claims (6)

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 an ultrasonic wave between the first and second transducers. A timing unit that starts and stops each time a sound wave propagates and measures a propagation time; a switching unit that reverses the transmission and reception directions of the first and second vibrators every time the measurement by the timing unit reaches a predetermined number of times; and A delay generating means for generating a minute time lag between the start or end of measurement of the time measuring means and the timing of transmission and reception; a measurement control means for controlling the delay generating means and the switching means; a measured value of the time measuring means; A flow rate calculating means for obtaining a flow rate based on a delay time of the delay generating means, wherein the measurement control means can change the delay time of the delay generating means by a predetermined range with a resolution smaller than the time resolution of the time measuring means. did Amount measuring device. 2. The flow rate measuring device according to claim 1, wherein the measurement control means determines the delay time setting range to be an integer multiple of the time resolution of the time measuring means. 2. The flow rate measuring device according to claim 1, wherein the measurement control means is configured to prohibit the next measurement for a predetermined time after the measurement by the time measuring means is completed. 3. The flow rate measurement according to claim 2, wherein the measurement control unit switches transmission / reception every time the set value of the delay generation unit circulates an integer number of times, and the flow rate calculation unit obtains the flow rate by measuring one pair of transmission / reception switching. apparatus. The flow rate measuring device according to claim 4, wherein the measurement control means determines the number of measurements until the flow rate calculation is performed as the measured flow rate decreases. The time measuring means comprises a synchronous clock generating means and a timer counter, and the measurement control means increases the synchronous clock oscillation period as the measured flow rate decreases, and the delay time setting resolution is the minimum synchronous clock oscillation period. The flow rate measuring device according to claim 4, wherein the flow rate measuring device is configured to be ½ or less of the above.

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