JP4476022B2 - Ultrasonic flow meter - Google Patents

Description

  The present invention relates to an improvement in an ultrasonic flow meter.

  Ultrasonic waves are transmitted and received between the ultrasonic transducers placed opposite to the upstream and downstream of the flow path, and the ultrasonic arrival time in the same direction as the flow (forward direction) and the ultrasonic wave in the direction opposite to the flow In a known ultrasonic flowmeter that measures the arrival time and calculates the flow rate based on both arrival times, it is necessary to measure the arrival time with high resolution in order to ensure a measurement system as a flow meter. To increase the resolution of arrival time measurement, it is conceivable to increase the frequency of the so-called reference clock used for time measurement. However, if the clock frequency is increased, the current consumption of the flow meter increases, so the battery is used as the power source. A battery-driven ultrasonic flowmeter is an obstacle to practical use.

  Therefore, when receiving the ultrasonic wave by the transmitter / receiver on the receiving side, transmitting the ultrasonic wave again from the transmitter / receiver on the transmitting side is repeated (transmitted) continuously several times to increase the substantial resolution of the arrival time measurement. A sing-around ultrasonic flowmeter is also well known. In this method, transmission / reception in the same direction is repeated 100 times, for example, and the resolution is substantially increased to 100 times by measuring 100 times the arrival time (total arrival time) collectively. However, since the number of repetitions of transmission / reception increases and the current consumption also increases, it becomes an obstacle to the practical use of a battery-driven ultrasonic flow meter.

  As described above, there has been proposed an ultrasonic flowmeter that increases measurement accuracy without relying on simply increasing the frequency of the reference clock or increasing the number of repetitions of transmission and reception. These will be described as the following first and second prior arts.

[First Prior Art] (see Patent Document 1)
In this method, the transmission timing is shifted each time with respect to the reference clock by a second clock having a frequency different from the reference clock for measuring the arrival time and a frequency that is not an integral multiple of the reference clock frequency, for example, a clock for clock. The oscillation of the reference clock is turned on in synchronization with the clock for clock, and ultrasonic waves are transmitted (transmitted) after a certain number of clocks from the clock. Then, the transmission timing is shifted in phase with respect to the reference clock each time by changing the predetermined number of clocks (incrementing by 1) for each transmission. Thus, the arrival time is obtained with high resolution from the average of a plurality of arrival times obtained by counting the reference clock. By doing so, it is said that a time resolution smaller than the period of the reference clock can be obtained.

In this prior art, if the transmission (transmission) timing is evenly distributed with no phase deviation with respect to the reference clock, the average value of a plurality of arrival time measurements by the reference clock approaches the correct value, and the error Although it should be possible to measure a small flow rate, it is difficult to shift the transmission timing uniformly in terms of phase. The phase is shifted by the difference between the two clock cycles (strictly, the difference between an integer multiple of the reference clock cycle and the clock clock cycle) due to slight deviation of the reference clock, temperature characteristics, etc. This is because the matching with (to what extent) increases. In particular, from the viewpoint of reducing power consumption, the reference clock may not use a high-accuracy clock oscillator such as a crystal oscillator in order to shorten the time from the start of oscillation until the frequency stabilizes. The period difference fluctuates due to a change in frequency, and the condition that the transmission timing is evenly distributed over one period of the reference clock phase tends to be broken. When evenly Chiraba to condition collapses, the average of multiple arrival time meter Hakachi is not approach the correct true value, the difference between the true value (error) is large. Therefore, there is a problem that the measurement accuracy (resolution) is not improved as expected.

[Second Prior Art] (see Patent Document 2)
Similar to the first prior art, this prior art can also be said to be aimed at obtaining a target (expected) high resolution at the average level of the arrival time of ultrasonic waves. Measurement by repeating transmission and reception a plurality of times is taken as one measurement set, forward measurement is performed with this measurement set, and then reverse measurement set is performed. In this way, several measurement sets are performed, and the flow rate is calculated based on the sum of the arrival time in the forward direction and the arrival time in the reverse direction, but any position from the start to the end of the measurement set The delay time is put in. The delay time is changed for each measurement set. For example, 1/10 of one cycle of the reference clock is defined as 1 unit, and each time, the delay time is gradually increased from 0 times (no delay) to 1 time, then 2 times, and 9 times the next time. Will return to 0 times again. In this way, it is said that it is possible to measure the arrival time with a resolution of 1/10 of the reference clock period by measuring 10 measurement sets. Actually, it is converted into a flow rate at every arrival time and averaged at the flow rate level.

In order for the average value to be the correct arrival time, if the unit of the delay time, that is, the basic delay time is 1 / n of the reference clock period, it is stopped when the delay time is increased up to n times (to the original one time) back) must (correctly starting from 0-fold (n-1) to fold or starting from 1-fold to up to n times, actually turn has one uniform respective multiples regardless Rayoi). The operation when n is 11 and the basic delay time is τ will be described with reference to FIG.

In FIG. 1, the count edge of the reference clock means the count edge of the reference clock by a counter that counts the reference clock. The first to twelfth times are the first measurement set to the twelfth measurement set, respectively. At the first time, the delay time is 0 (that is, there is no delay), the first transmission (first transmission) is performed at the time of the first count edge, and the continuous repetition of a plurality of times of transmission and reception ends at the time of the final reception. is doing. FIG. 1 shows a case where the arrival time from the first transmission to the final reception when the delay time is 0 is 1.3 in terms of the reference clock cycle (number of clocks), but there is actually no such case. In FIG. 1, 1/11 of the reference clock period is 1 unit (τ), and the delay time is increased from 0 times to 1 time, 2 times,... The target delay time τ is aimed at a configuration in which the arrival time can be measured with a resolution of 1/11 of the reference clock period in 11 measurements (measurement set) by returning to 0 times. Shows a case where it becomes 1/10 of the reference clock period for some reason (for example, due to a temperature change or the like) and becomes larger than the planned 1/11. The count value of the first reference clock is 1, first to 7 th is count value both is 1. To 11 th 8 th is 2 both are count values. The delay time returns to 0 at the 12th time. Therefore, the average value of the arrival times from the first time to the eleventh time is the average value of the count values from the first time to the eleventh time, which is about 1.4 as shown in the following equation, and is true (1 × 7 + 2 × 4) / 11 = 1.36 ≒ 1.4
The value is far from 1.3.

In the second prior art, in order to improve the measurement resolution, it is necessary to set the basic delay time τ small, and a delay element is used as the delay means. However, the delay time of the element is affected by the temperature change. Therefore, there is a problem that the measurement accuracy (resolution) is not improved as much as expected. This is because the matching of the basic delay time τ and how many times the delay time is increased is broken by a temperature change or the like.
JP 2002-5706 ([0013], FIG. 2) JP 2003-232664 A ([0019] to [0022])

  As described above, in the first conventional technique, when the clock frequency slightly changes due to a temperature change or the like, the condition that the transmission timing is evenly distributed in one phase of the phase of the reference clock is broken, and as a result, a plurality of measurements are performed. There is a problem that the average value of the values deviates from the correct value and the measurement accuracy (resolution) is not improved as expected.

In the second prior art, if there is a delay in the time change of the delay element due to temperature changes, as before mentioned, the basic delay time, collapse that of matching to increase the delay time to many times, the results Therefore, there is a problem that correct measurement values cannot be obtained and the measurement accuracy (resolution) is not improved as expected.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an ultrasonic flowmeter that can solve the problems of the prior art, increase the substantial resolution of ultrasonic arrival time measurement, and achieve high accuracy of flow measurement. .

In the present invention, the first transmission is performed with a delay time from the count edge of the reference clock, the sequential delay time for each transmission is increased by a fixed time, and the transmission (transmission) timing is after the next count edge of the reference clock. The main feature is that the delay time is returned to the delay time at the first transmission.
The invention of claim 1 are mutually send and receive ultrasonic waves between the ultrasonic transducer which is arranged to face the upstream and downstream fluid, the ultrasonic flowmeter seeking by Ri flow amount thereof arrival time,
Measure the arrival time from the first transmission to the last reception, that is, measure the reference clock from the start to the end of the arrival time measurement,
Perform the first transmission with a delay from the reference clock count edge,
The delay is an integral multiple of a fixed time less than one period of the reference clock;
Start with 1 time of the fixed time, and increase the multiple by 1 for each measurement each time,
When the transmission timing comes after the next count edge of the reference clock, the ultrasonic flowmeter is characterized in that the next measurement delay time is returned to one time of the predetermined time.

The operation of the present invention will be described with reference to FIG. FIG. 2 shows a case where the arrival time, that is, the first transmission (transmission) to the final reception is 1.3 in terms of the number of reference clocks, but there is actually no such case. It makes it easy to understand the operation of the invention. An interval (time) between adjacent count edges is one cycle of the reference clock, and a fixed time smaller than this one cycle is denoted by τ. The delay time at the first measurement is τ × 1, and at the next second measurement, τ × 2 and the delay time are increased in order, and at the tenth time, the delay time is τ × 10. In other words, the first transmission (at the time of transmission) at the start of measurement is the count edge (the leftmost count edge in FIG. 2) that started the delay, and the center of the three count edges in FIG. After the count edge). Therefore, in the next (11th) measurement, the delay time is returned to the basic fixed time τ. By repeating this operation, as shown in FIG. 2, the count value obtained by counting the count edges of the reference clock from the start of measurement, that is, from the first transmission (transmission) to the last reception (final reception), As shown at the right end of FIG. 2, the arrival time is 1 for the 1st to 6th times, 2 for the 7th to 9th times, and 1 for the 10th time, and the average value for 10 times is (1 × 7 + 2 × 3) / 10. = 1.3 and the arrival time is accurately measured. In this way, a value close to the true value of the arrival time (the same measured value as the true value in the example of FIG. 2) is obtained. In FIG. 2, when the delay time is increased to 10 times the fixed time τ, the transmission (transmission) timing comes after the next count edge of the reference clock. While returning value tau × 1 or, when if a predetermined time tau is that it has become about 90% of the time, will be increased to the next exceeds count edge 11 times the delay time, start the measurement of the 11 th The time points (first transmission in FIG. 2) are evenly arranged over one period of the reference clock, and the average of the measured values (count values) of the arrival times is close to the true value.

In FIG. 2, the delay time starts from 1 time of the basic fixed time τ, and increases by 2 times, 3 times,..., 10 times in order for each measurement, and the first transmission (transmission) is the next count edge of the reference clock. once beyond the (When only after the next count edge), but to repeat to return to 1 times τ in the next 11 th measurement, even starting from 0 times the base of a predetermined time τ , by setting significantly smaller than one period of the reference clock for a predetermined time, the same effect as when starting from 1-fold tau × 1 as described above can be expected.

  In addition, when the start of measurement exceeds the next count edge, a method of sequentially reducing the delay time from the next time is also conceivable. Decrease an integer multiple of a fixed time one by one for each measurement, and when it becomes 1, increase the number of multiples one by one from the next time. Even if it repeats, the equivalent result is obtained.

The invention of claim 2, mutually transmits and receives ultrasonic waves between the ultrasonic transducer which is arranged to face the upstream and downstream fluid, the ultrasonic flowmeter seeking by Ri flow amount thereof arrival time,
Measure the arrival time from the first transmission to the last reception, that is, measure the reference clock from the start to the end of the arrival time measurement,
Perform the first transmission with a delay from the reference clock count edge,
The delay is an integral multiple of a fixed time less than one period of the reference clock;
Start with 1 time of the fixed time, and increase the multiple by 1 for each measurement each time,
When the delay time exceeds a certain integer multiple of one cycle of the reference clock, the next measurement is an ultrasonic flowmeter in which the delay time is returned to one time of the certain time.

  Since the average value of several measurement values is an accurate value close to the true value, it is not necessary to increase the frequency of the reference clock so much, and it is not necessary to increase the number of times of repeated sending and receiving of the single around. Therefore, the measurement accuracy can be improved without increasing the current consumption, which contributes to the practical application of a battery-driven ultrasonic flow meter.

Also, since the phase at the measurement start time (first transmission time) of the arrival time is different for each measurement with respect to the reference clock, the phase is also different from the noise synchronized with the reference clock every time, and the influence of the noise is averaged. To reduce adverse effects. Therefore, S / N of the arrival time measurements improved and also leads to increased flow rate measurement accuracy from this plane.

  The amount of phase shift with respect to the reference clock (that is, the predetermined time) at the start of measurement due to each delay is not necessarily an integral number of one cycle of the reference clock. In that case, the deviation becomes a measurement error, but in the invention of claim 2, the phase shift at the measurement start time is performed over a plurality of cycles instead of one cycle of the reference clock, so that more equalization can be realized. The error in the arrival time measurement can be reduced and the flow measurement accuracy is further improved.

  The frequency of the reference clock for measuring the arrival time of the ultrasonic wave is set to a particularly high frequency, or the number of repeated transmissions and receptions in the sing-around method is further increased to avoid an increase in current consumption. By shifting the phase at the start of measurement in order and performing several measurements, the measurement error was reduced and the flow measurement accuracy was improved.

  Next, Example 1 will be described with reference to FIGS. FIG. 4 is a block diagram showing the configuration of Embodiment 1 of the present invention. As shown in FIG. 5, the transducers 1 and 2 can be used for both transmission and reception by ultrasonic transducers arranged opposite to each other in the fluid of the flow tube 3 at a distance L upstream and downstream. Both transducers transmit and receive ultrasonic waves in the fluid in the forward direction from upstream to downstream and in the reverse direction from downstream to upstream. In FIG. 2, V indicates the flow rate of the fluid.

  The roles of the transducers 1 and 2 are determined according to the state of the changeover switches 3 and 4. When the change-over switches 3 and 4 are in the illustrated state, the transmitter / receiver 1 functions as a transmission side, and the transmission wave device 2 functions as a reception side. The reception wave detector 5 is connected to a transmission wave transmitter 2 on the reception side and outputs a reception wave detection signal when a reception wave is detected. As shown in FIG. 7, the reception wave detection unit 5 is mainly composed of an amplifier 6 and comparators 7 and 8, and first amplifies a reception signal from a reception-side transmitter / receiver, for example, the transmitter / receiver 2. FIG. 6 shows the received wave after amplification. FIG. 6 also shows a drive signal for transmission. After the drive signal, the received wave is received by the transmitter, for example 2, after the propagation time indicated by the symbol t, and the received wave detection signal is output at the zero-cross point C of the third wave.

The received wave detection unit 5 amplifies the received signal , and the signal is input to the comparators 7 and 8, and the zero cross point C immediately after detecting the third wave by comparison with the reference voltage V _TH is set to the zero level. Are detected and output as a received wave detection signal. The outputs of the comparators 7 and 8 are sent to the next gate 11 via the gates 9 and 10, respectively, and the received waves reach these gates 9, 10 and 11. It is designed to open just before. In this way, even if the unexpected noise while these gates are closed is mistakenly detected as a received wave, it is prevented from being sent to the next stage because the gate is closed. In this way, malfunction due to sudden noise can be prevented and highly accurate measurement can be performed. The timing for opening the gate is determined so as to pass only the signal that detects the true received wave as much as possible, taking into account the distance L between the transducer, the flow velocity range, and the temperature range.

  In FIG. 4 again, the control unit 12 sends a transmission / reception switching signal for switching the change-over switches 3 and 4 at regular time intervals, and after switching between transmission and reception, that is, transmission / reception, the reference clock of the reference clock generation unit 13 The start signal is output to the delay unit 15 at the same timing as the count edge (the edge counted by the counter 14).

When receiving the start signal from the control unit 12, the delay unit 15 outputs a drive signal after a certain delay time. The delay unit 15 has the configuration shown in the block diagram of FIG. The start signal from the control unit 12 is input to the delay element unit 16 and the measurement number counter 17. The measurement number counter counts the number of measurements by counting the start signal, and sends the count value to the data selector 18 as a select signal (selection signal). The data selector 18 selects the output signal (delay signal) of the delay element unit 16 according to the select signal from the measurement number counter 17 and outputs it as a drive signal. The reference clock and the drive signal are input to a delay upper limit detection unit 19 that detects the upper limit of the delay time. When the detection unit 19 detects the upper limit of the delay time and outputs a reset signal, the count value of the measurement number counter 17 is reset. It is configured to be.

  As shown in FIG. 9, the delay element unit 16 includes a plurality of delay elements 21, 22, 23,... The time is set to be an integral multiple of the basic delay time (fixed time), and this integer is selected by the select signal which is the count value of the measurement number counter 17. And, every two measurements (every one measurement in each of the forward and reverse directions), an integer multiple is sequentially increased by 1, 2, 3,. When the first drive signal output comes after the count edge of the first reference clock after the start signal from the control unit 12, the number passing through the delay element is set to one for the second (next) next measurement. I'm trying to get it back. Thus, increasing the number of passing delay elements by one every two measurements increases the delay time for each set of the forward direction and the reverse direction of the transmission direction, that is, the delay time is increased by 1 for each direction. This is to increase by one (a certain time).

When receiving the drive signal from the delay unit 15, the transmitter drive unit 31 of FIG. 4 drives the transmitter / receiver, for example, the transmitter / receiver 1.

  The counter 14 measures the time from the drive signal to the received wave detection signal. The control unit 12 reads the measured time (reference clock count value). In this embodiment, the counter value of the counter 14 is cleared to zero by the start signal and starts counting.

Control unit 12 by the switching of the changeover switch 3 and 4 by inverting the received switching signal transmission at a predetermined time interval, performs two transducer 1 and switching of roles between transmission and reception of two.

  After each switching, a start signal is output after a time when a transient phenomenon such as noise due to switching is settled. Then, when the received wave detection signal is input, the arrival time (count value) measured by the counter 14 is read, and the flow rate between them is measured based on both measured values using the measured value in the opposite direction performed immediately before.・ Calculate the flow rate.

According to this embodiment, the measurement of the arrival time of each direction, particularly the timing of timing at which drive motion signal to start the measurement for each measurement initiation, since the shifted by the delay elements 1 delay time, for each direction The measurement is optimally shifted in phase each time with respect to the reference clock. For this reason, the average value is close to the true value of the arrival time in each direction, and the flow velocity and flow rate calculated using the values are close to the true value, so that highly accurate measurement with small errors is possible.

  FIG. 10 is a block diagram showing the overall configuration of another embodiment. In this second embodiment, in order to further improve the resolution (accuracy), transmission / reception is continuously repeated a predetermined number of times and applied to a method of measuring the arrival times for a predetermined number of times collectively.

  In the following, parts different from the first embodiment will be mainly described. When receiving the drive signal from the delay unit 15, the transmitter drive unit 31 </ b> A first drives the transmitter-side transmitter / receiver, for example, the transmitter / receiver 1, and then drives whenever a received wave detection signal is received from the received wave detection unit 5. To do. However, when the nth received wave drive signal is received from the first counter 14A, the drive is stopped until a drive signal based on the start signal from the control unit 12A is newly received. In this embodiment, meaningless (n + 1) th driving is performed, but there is no problem because it is ignored on the receiving side.

Also in the present embodiment, the received wave detection unit 5 is mainly composed of an amplifier and a comparator. After amplifying a signal from the transmitter / receiver on the receiving side, the signal is input to the comparator, and the reference voltage V Compared to _TH , the zero cross point immediately after detection of the third wave is detected by comparison with zero level and output as a received wave detection signal.

  The outputs of these comparators are respectively sent to the next stage through gates, and the gates are set to “open” immediately before the reception wave arrives. By doing so, the comparator erroneously detects noise other than the received wave, and even if an abnormal signal is output, it is not sent to the next stage.

  In this embodiment, in the second and subsequent receptions, the “open” timing of the gate is obtained from the previous arrival time, the previous arrival time is stored, and the time since the transmission of that time is stored. When a value obtained by subtracting a predetermined time from the set time is “open”.

  By doing so, it is possible to “open” the gate immediately before the received wave arrives, effectively blocking noise and capturing only the original received wave.

  This “open” timing can be determined by taking into account the average value of several arrival times in the past.

  The counter 14A counts the number of received wave detection signals from the received wave detection unit 5 and outputs the received signal as an nth received wave detection signal when the nth received wave detection signal is received. The counter 14A is reset by a start signal from the control unit 12A.

The counter 14B collectively measures the time from the drive signal to the nth received wave detection signal, that is, the total arrival time from the first transmission to the last reception of n consecutive repeated transmissions / receptions. The measured value (count value) of the control unit 12A takes to read. In this embodiment, the count value is cleared to zero by the start signal and starts counting.

Control unit 12A, the n-th received Namiken known signal is input, reading the measured value of the counter 14B (count value), using the measured values at the opposite went immediately before, during flow rate Flow rate Is calculated. In this example, n consecutive repeated transmissions / receptions are performed for each measurement in one direction, the arrival times for n times are collectively measured, and the flow velocity and flow rate are calculated based on this, so compared with Example 1. Thus, measurement with higher resolution (high accuracy) becomes possible.

  Also in the second embodiment, as in the first embodiment, the delay time is two times later when the drive signal output is after the count edge input of the first reference clock after the start signal from the control unit (next time). In the next measurement, the number passing through the delay element is returned to one.

  The overall configuration of the present embodiment is the same as the block diagram of FIG. 10 of the second embodiment, and only part of the operation is different. That is, in the second embodiment, as described above, when the drive signal output is after the count edge of the “first reference clock after the start signal” is input from the control unit, the delay time is two times later (next next time). ), The number of passing through the delay element is returned to one, but in the third embodiment, the “first reference clock after the start signal” is not “the fifth reference clock after the start signal”. The first transmission timing is scattered evenly in phase with respect to the reference clock as the count edge, and the average value of the arrival times becomes closer to the true value. The third embodiment corresponds to the invention of claim 2.

This embodiment, configuration of the entire body only the configuration of the same delay unit and FIG. 4 is different. A block diagram of the configuration of the delay unit 15 is shown in FIG.

  The delay time can be set to an integer multiple of the clock period of the oscillator 33 by counting (counting) the clock output from the oscillator 33 that starts oscillation when the start signal is input. The output clock of the oscillator 33 is input to the counter 34, and when the start signal is input to the oscillator 33 of the delay unit 15, the oscillator 33 starts oscillating and the output clock is counted by the counter 34. The count value that is the output of the counter 34 is compared with the output of the measurement number counter 35 that operates as a preset counter by the coincidence detector 36, and when the count value that is the output of the counter 34 matches the output of the measurement number counter 35, A coincidence signal that is an output of the coincidence detection unit 36 is input to the gate control unit 37. The coincidence signal inputted to the gate control unit 37 is normally inputted as an open signal to the gate unit 38 as it is, and when the open signal becomes “open”, the output of the oscillator 33 is outputted to the gate unit only once. 38 is allowed to pass as a drive signal. The start signal is a count input of the measurement number counter 35, and is counted up by one count every time the start signal is input, that is, every measurement. Therefore, the output timing of the coincidence signal, which becomes the output timing of the drive signal at the end timing of the delay time, is delayed every time one cycle of the output clock of the oscillator 33.

  However, at the base point, when a start signal is input, the oscillator 33 starts to oscillate, and the counter 34 counts (counts) the output clock. In this embodiment, when one reference clock is input, the gate control unit 37 outputs an open signal, and at the same time, the output (count value) of the counter 34 at that time is preset and stored in the measurement number counter 35. ing.

  In the next measurement, when the start signal is input, the oscillator 33 and the counter 34 start to operate, and the measurement number counter 35 is incremented by 1, so that the coincidence signal is a time that is one clock longer than the number of output clocks from the oscillator 33. Is output when In other words, an open signal from the gate control unit 37 to the gate unit 38 is also output at a time one clock later from the start signal. Thereafter, the time from the start signal to the drive signal, that is, the delay time becomes longer every measurement time.

  In the gate control unit 37. Further, when the drive signal and the reference clock are compared, when the reference clock of the fourth pulse after the start signal (in this embodiment) is input earlier than the drive signal, it returns to the base point in the next measurement. ing.

  In this way, the delay time can be evenly distributed from 1 to 4 times the reference clock. That is, since the transmission timing can be evenly distributed with respect to the reference clock, the average value of arrival times approaches the true value. In this embodiment, the delay time is increased for each measurement without distinguishing between forward and reverse measurements. However, since the measurement in the forward direction and the reverse direction are measured in pairs, this method has the same effect. . It is also possible to increase the delay time for each pair by setting the measurement in the forward direction and the reverse direction as a pair as in the previous embodiment in the direction such as placing a 1/2 frequency divider in front of the measurement number counter 35. is there.

The present invention is applicable to a flow meter such as a gas meter.

The figure explaining operation | movement of a prior art. The figure explaining operation | movement of Claim 1 of this invention. The figure explaining operation | movement of Example 4 of this invention. 1 is a block diagram of Embodiment 1 of the present invention. The figure which shows arrangement | positioning of the amount of transmission / reception in a flow tube. The figure which shows the waveform of a drive signal and a received wave. The block diagram of the received wave detection part of FIG. The block diagram of the delay part of FIG. The block diagram of the delay element part of FIG. The block diagram of Example 2 of this invention. The block diagram of Example 4 of this invention.

Explanation of symbols

1, 2 Transceiver 3 Flow tube 13 Reference clock generator 15 Delay unit 14, 14A, 14B Counter τ Fixed time (basic delay time)

Claims (2)

Mutually send and receive ultrasonic waves between the ultrasonic transducer which is arranged to face the upstream and downstream fluid, the ultrasonic flowmeter seeking by Ri flow amount thereof arrival time,
Measure the arrival time from the first transmission to the last reception, that is, measure the reference clock from the start to the end of the arrival time measurement,
Perform the first transmission with a delay from the reference clock count edge,
The delay is an integral multiple of a fixed time less than one period of the reference clock;
Start with 1 time of the fixed time, and increase the multiple by 1 for each measurement each time,
An ultrasonic flowmeter characterized in that when the transmission timing comes after the next count edge of the reference clock, the next measurement returns the delay time to one time of the predetermined time. Mutually send and receive ultrasonic waves between the ultrasonic transducer which is arranged to face the upstream and downstream fluid, the ultrasonic flowmeter seeking by Ri flow amount thereof arrival time,
Measure the arrival time from the first transmission to the last reception, that is, measure the reference clock from the start to the end of the arrival time measurement,
Perform the first transmission with a delay from the reference clock count edge,
The delay is an integral multiple of a fixed time less than one period of the reference clock;
Start with 1 time of the fixed time, and increase the multiple by 1 for each measurement each time,
An ultrasonic flowmeter characterized in that if the delay time exceeds a certain integral multiple of one period of the reference clock, the next measurement returns the delay time to one time of the predetermined time.

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