Flow rate measurement device

Abstract

This flow rate measurement device comprises: a reception detection means for detecting an ultrasonic signal transmitted from one ultrasonic transducer and received by another ultrasonic transducer; a first timer that measures a first time that is the time from when the ultrasonic signal is transmitted from the one ultrasonic transducer to a change timing at which a value of a clock pulse changes; a second timer that measures a second time that is the time from when the ultrasonic signal received by the other ultrasonic transducer is detected by the reception detection means to the change timing; and a calculation means for calculating a flow rate of fluid on the basis of the first time and the second time. A driving means varies, by only a predetermined time, a transmission timing of a drive signal in a case in which the flow rate calculated by the calculation means is equal to or less than a threshold, and a transmission timing in a case in which the flow rate exceeds the threshold.

Description

Flow Metering Device

[0001] The present disclosure relates to a flow rate measurement device that uses ultrasound to measure the flow rate of a fluid such as gas or water.

[0002] Conventionally, in an ultrasonic flow meter, it is known to calculate the propagation time of ultrasonic waves based on the time measured by two timers, a first timer with low measurement resolution and a second timer with high measurement resolution, and thereby determine the flow rate of a fluid (Patent Document 1).

[0003] In detail, the control unit outputs a measurement start signal to the drive circuit and simultaneously starts timing by the first timer. Upon receiving the signal, the drive circuit drives the first ultrasonic transducer to emit ultrasonic waves. The emitted ultrasonic waves propagate through the fluid and are received by the second ultrasonic transducer, which is provided downstream of the first ultrasonic transducer. The ultrasonic signal received by the second ultrasonic transducer is received by the reception detection circuit, which outputs a signal based on the ultrasonic signal to the first timer and the second timer. The second timer starts timing upon receiving a signal from the reception detection circuit and stops timing at the count-up timing of the first timer. The first timer stops timing at the count-up timing. The propagation time is then calculated based on the timing results of the first timer and the second timer.

[0004] The ultrasonic wave transmitting side and receiving side are switched between the first ultrasonic transducer and the second ultrasonic transducer. For example, after the first ultrasonic transducer transmits ultrasonic waves as the transmitting side, the second ultrasonic transducer is switched to the transmitting side and transmits ultrasonic waves. Then, the propagation time is calculated for each aspect of ultrasonic wave transmission, and the flow rate is calculated based on the difference between these two propagation times.

[0005] Japanese Patent Application Laid-Open No. 2000-213971

[0006] However, when the flow rate of the fluid flowing through the measurement flow path is low, that is, when the difference between one propagation time and the other propagation time is small, if the end of the propagation time falls around the time when the clock pulse value of the first timer switches, the accuracy of the flow rate calculation decreases. That is, the maximum error occurs in one of the two propagation times, and the minimum error occurs in the other, resulting in a large error in the flow rate calculated based on the difference between the two propagation times as described above.

[0007] Therefore, an object of the present disclosure is to provide a flow rate measurement device that can calculate a flow rate with high accuracy.

[0008] The flow rate measuring device of the present disclosure includes a first ultrasonic transmitter / receiver and a second ultrasonic transmitter / receiver that are provided in a measurement flow path and transmit and receive ultrasonic signals; a drive means that transmits a drive signal to the first ultrasonic transmitter / receiver or the second ultrasonic transmitter / receiver; a reception detection means that detects the ultrasonic signal transmitted from one of the first ultrasonic transmitter / receiver and the second ultrasonic transmitter / receiver in response to the drive signal and received by the other ultrasonic transmitter / receiver; a first timer that outputs clock pulses at a predetermined cycle and counts the clock pulses to measure a first time period that is a time from when the ultrasonic signal is transmitted from one of the ultrasonic transmitter / receivers to when the value of the clock pulse changes after a predetermined condition is satisfied; and a second timer that outputs clock pulses at a predetermined cycle and counts the clock pulses to measure a first time period that is a time period from when the ultrasonic signal is transmitted from one of the ultrasonic transmitter / receivers and received by the other ultrasonic transmitter / receiver. The fluid flow rate control system includes a second timer that measures a second time, which is the time from detection to the timing of the change; a control means that controls the operation of the first timer and the second timer; and a calculation means that calculates a flow rate of a fluid based on a first propagation time obtained based on the first time and the second time in a mode in which an ultrasonic signal is transmitted from one ultrasonic transmitter / receiver to the other ultrasonic transmitter / receiver, and a second propagation time obtained based on the first time and the second time in a mode in which an ultrasonic signal is transmitted from the other ultrasonic transmitter / receiver to the one ultrasonic transmitter / receiver, wherein the driving means transmits the driving signal based on a clock pulse output by the first timer, and differentiates by a predetermined time the transmission timing of the driving signal when the flow rate calculated by the calculation means is equal to or less than a threshold value and the transmission timing when the flow rate exceeds the threshold value.

[0009] According to the present disclosure, when the flow rate is equal to or less than a threshold value, the driving means executes a process of shifting the transmission timing of a drive signal, based on a clock pulse output by a first timer, by a predetermined time from the transmission timing when the flow rate exceeds the threshold value. This allows the second time used to calculate the first propagation time and the second time used to calculate the second propagation time to be approximately equal. Therefore, for example, when calculating the flow rate using an arithmetic expression that includes the difference between the first and second propagation times as one element of the calculation, the error in the first propagation time and the error in the second propagation time are approximately canceled out. This improves the accuracy of the flow rate calculation.

[0010] The flow rate measurement device of the present disclosure includes a first ultrasonic transmitter / receiver and a second ultrasonic transmitter / receiver that are provided in a measurement flow path and transmit and receive ultrasonic signals; a drive means that transmits a drive signal to the first ultrasonic transmitter / receiver or the second ultrasonic transmitter / receiver; a reception detection means that detects the ultrasonic signal transmitted from one of the first ultrasonic transmitter / receiver and the second ultrasonic transmitter / receiver in response to the drive signal and received by the other ultrasonic transmitter / receiver; a first timer that outputs clock pulses at a predetermined cycle and counts the clock pulses to measure a first time period that is a time from when the ultrasonic signal is transmitted from one of the ultrasonic transmitter / receivers to when the value of the clock pulse changes after a predetermined condition is satisfied; and a second timer that outputs clock pulses at a predetermined cycle and counts the clock pulses to measure the first time period that is a time period from when the ultrasonic signal is transmitted from one of the ultrasonic transmitter / receivers to when the value of the clock pulse changes after a predetermined condition is satisfied. a second timer that measures a second time, which is the time from when the first timer is turned on to when the change timing occurs; a control means that controls the operation of the first timer and the second timer; and a calculation means that calculates a flow rate of a fluid based on a first propagation time obtained based on the first time and the second time in a mode in which an ultrasonic signal is transmitted from one ultrasonic transmitter / receiver to the other ultrasonic transmitter / receiver, and a second propagation time obtained based on the first time and the second time in a mode in which an ultrasonic signal is transmitted from the other ultrasonic transmitter / receiver to the one ultrasonic transmitter / receiver, wherein the control means stops the time counting by the second timer based on a clock pulse output by the first timer, and differentiates by a predetermined time the stop timing of the second timer when the flow rate calculated by the calculation means is equal to or less than a threshold value and the stop timing when the flow rate exceeds the threshold value.

[0011] According to the present disclosure, when the flow rate is equal to or less than a threshold value, the control means executes a process of changing the stop timing of the second timer, which is based on the clock pulse output by the first timer, by a predetermined time from the stop timing when the flow rate exceeds the threshold value. This allows the second time used to calculate the first propagation time and the second time used to calculate the second propagation time to be approximately equal. Therefore, for example, when calculating the flow rate using an arithmetic expression that includes the difference between the first propagation time and the second propagation time as one element of the calculation, the error in the first propagation time and the error in the second propagation time are approximately canceled out. This improves the accuracy of the flow rate calculation.

[0012] In the above disclosure, the predetermined time may be half the time of one cycle of a clock pulse output by the first timer.

[0013] According to the above configuration, the possibility that the error in the first propagation time and the error in the second propagation time will cancel each other out increases, thereby further improving the accuracy of the flow rate calculation.

[0014] In the above disclosure, when the ratio of the second time measured by the second timer to the first time measured by the first timer is equal to or less than a first predetermined value or the ratio of the second time to the first time is equal to or greater than a second predetermined value, the driving means may differentiate by a predetermined time the transmission timing of the drive signal when the ratio of the second time to the first time is equal to or less than the first predetermined value or the ratio of the second time to the first time is equal to or greater than the second predetermined value, from the transmission timing when the ratio of the second time to the first time exceeds the first predetermined value or the ratio of the second time to the first time is less than the second predetermined value.

[0015] According to the above configuration, the second time used to calculate the first propagation time and the second time used to calculate the second propagation time can be made to have a value that is more equal to each other, thereby almost canceling out the error in the first propagation time and the error in the second propagation time, thereby improving the accuracy of calculating the flow rate.

[0016] In the above disclosure, when the ratio of the second time measured by the second timer to the first time measured by the first timer is equal to or less than a first predetermined value or the ratio of the second time to the first time is equal to or greater than a second predetermined value, the driving means may differentiate by a predetermined time the stop timing of the second timer when the ratio of the second time to the first time is equal to or less than the first predetermined value or the ratio of the second time to the first time is equal to or greater than the second predetermined value from the stop timing when the ratio of the second time to the first time exceeds the first predetermined value or the ratio of the second time to the first time is less than the second predetermined value.

[0017] According to the above configuration, the second time used to calculate the first propagation time and the second time used to calculate the second propagation time can be made to have a value that is more equal to each other, thereby almost canceling out the error in the first propagation time and the error in the second propagation time, thereby improving the accuracy of calculating the flow rate.

[0018] According to the present disclosure, it is possible to provide a flow rate measurement device that is capable of calculating a flow rate with high accuracy.

[0019] 4(a) is a block diagram showing the configuration of a flow rate measurement device according to an embodiment; FIG. 4(b) is a diagram showing a first time measured by a first timer and a second time measured by a second timer; and FIG. 4(b) is a diagram for explaining count-up by the second timer. (a) is a diagram showing the relationship between calculated propagation time and actual propagation time when there is no normalization error, and (b) is a diagram showing the relationship between calculated propagation time and actual propagation time when there is a normalization error. (b) is a diagram showing changes in flow rate calculated based on the calculated propagation time in FIG. 4(b). (a) is a diagram showing the time measured by the second timer when a drive signal is transmitted to an upstream ultrasonic transmitter / receiver at the rising edge of a clock pulse generated by the first timer, and (b) is a diagram showing the time measured by the second timer when a drive signal is transmitted to a downstream ultrasonic transmitter / receiver at the rising edge of a clock pulse generated by the first timer. (a) is a diagram showing the time measured by the second timer when a drive signal is transmitted to an upstream ultrasonic transmitter / receiver at the falling edge of a clock pulse generated by the first timer, and (b) is a diagram showing the time measured by the second timer when a drive signal is transmitted to a downstream ultrasonic transmitter / receiver at the falling edge of a clock pulse generated by the first timer. (a) is a diagram showing the time measured by the second timer when the counting by the second timer is stopped at the falling edge of the clock pulse by the first timer when a drive signal is sent to an upstream ultrasonic transmitter / receiver, and (b) is a diagram showing the time measured by the second timer when the counting by the second timer is stopped at the falling edge of the clock pulse by the first timer when a drive signal is sent to a downstream ultrasonic transmitter / receiver.

[0020] Hereinafter, a flow measurement device according to an embodiment of the present disclosure will be described with reference to the drawings. The flow measurement device described below is merely one embodiment of the present disclosure. Therefore, the present disclosure is not limited to the following embodiment, and additions, deletions, and modifications are possible within the scope of the present disclosure.

[0021] Fig. 1 is a block diagram showing the configuration of a flow rate measurement device 100 according to one embodiment. Fig. 2 is a diagram showing a first time measured by a first timer 7 and a second time measured by a second timer 8.

[0022] As shown in FIG. 1, the flow rate measuring device 100 of this embodiment includes a measurement flow path 1, a first ultrasonic transmitter / receiver 2, a second ultrasonic transmitter / receiver 3, a driving means 4, a switching means 5, a receiving and detecting means 6, a first timer 7, a second timer 8, a control means 9, and a calculation means 10.

[0023] The flow measurement device 100 has a CPU and a storage unit (ROM, RAM, EEPROM, HDD, etc.) (not shown). The CPU executes a predetermined program stored in the storage unit, thereby functionally realizing the above-mentioned driving means 4, switching means 5, reception detection means 6, control means 9, and calculation means 10. The CPU may be implemented as a single processor, or as multiple processors that cooperate with each other.

[0024] The measurement flow path 1 is formed in a tubular shape and is a flow path for a fluid that extends in one direction and is provided in a housing (not shown) of the flow measurement device 100. Examples of the fluid in this embodiment include water and gas.

[0025] The first ultrasonic transmitter / receiver 2 and the second ultrasonic transmitter / receiver 3 are arranged in the measurement flow path 1 along the fluid flow direction. The first ultrasonic transmitter / receiver 2 is arranged downstream of the second ultrasonic transmitter / receiver 3 in the fluid flow direction. The first ultrasonic transmitter / receiver 2 can transmit ultrasonic waves to the second ultrasonic transmitter / receiver 3, and can receive ultrasonic waves transmitted from the second ultrasonic transmitter / receiver 3. The second ultrasonic transmitter / receiver 3 can transmit ultrasonic waves to the first ultrasonic transmitter / receiver 2, and can receive ultrasonic waves transmitted from the first ultrasonic transmitter / receiver 2. In this case, ultrasonic waves transmitted from the first ultrasonic transmitter / receiver 2 or the second ultrasonic transmitter / receiver 3 propagate through the fluid and are received by the second ultrasonic transmitter / receiver 3 or the first ultrasonic transmitter / receiver 2.

[0026] The driving means 4 drives the first ultrasonic transmitter / receiver 2 and the second ultrasonic transmitter / receiver 3 via the switching means 5. The driving means 4 applies, for example, a burst wave as a drive signal to the first ultrasonic transmitter / receiver 2 and the second ultrasonic transmitter / receiver 3 via the switching means 5.

[0027] The switching means 5 switches the target for receiving the drive signal from the driving means 4 to one of the first ultrasonic transmitter / receiver 2 and the second ultrasonic transmitter / receiver 3. When the target for receiving the drive signal from the driving means 4 is switched to the first ultrasonic transmitter / receiver 2 by the switching means 5, the first ultrasonic transmitter / receiver 2 transmits an ultrasonic signal, and the second ultrasonic transmitter / receiver 3 receives the ultrasonic signal. On the other hand, when the target for receiving the drive signal from the driving means 4 is switched to the second ultrasonic transmitter / receiver 3 by the switching means 5, the second ultrasonic transmitter / receiver 3 transmits an ultrasonic signal, and the first ultrasonic transmitter / receiver 2 receives the ultrasonic signal.

[0028] The reception detection means 6 detects an ultrasonic signal transmitted from one of the first ultrasonic transmitter / receiver 2 and the second ultrasonic transmitter / receiver 3 in response to the drive signal, propagates through the fluid, and is then received by the other ultrasonic transmitter / receiver. When the reception detection means 6 receives an ultrasonic signal, it outputs a predetermined signal to the second timer 8. The point in time when the ultrasonic waves transmitted by the transmitting ultrasonic transmitter / receiver are received by the receiving ultrasonic transmitter / receiver is generally called the zero-crossing point. This zero-crossing point is the point in time when the voltage of the amplified signal changes from positive to negative for the first time after the voltage of the amplified signal exceeds the reference voltage. The elapsed time from the point in time when the ultrasonic signal is transmitted by the transmitting ultrasonic transmitter / receiver to the zero-crossing point corresponds to the propagation time of the ultrasonic signal.

[0029] The first timer 7 includes an oscillator that vibrates at a low frequency (e.g., 100 kHz to 10 MHz), an output unit that outputs clock pulses based on the oscillation of the oscillator, and a counter that counts the number of cycles of the clock pulses, i.e., the number of clock pulses. The oscillator of the first timer 7 is, for example, a ceramic oscillator. The time resolution of the first timer 7 is, for example, 250 ns. The first timer 7 measures a first time, which is the time from when an ultrasonic signal is transmitted from one ultrasonic transmitter / receiver to the change timing at which the value of the clock pulse output by the first timer 7 changes after a zero-crossing point has passed as a predetermined condition. In this embodiment, the first timer 7 starts timing from the time when a drive signal is provided to one ultrasonic transmitter / receiver by the driving means 4 via the switching means 5, which is defined as the time when an ultrasonic signal is transmitted from one ultrasonic transmitter / receiver. The change timing is, for example, the rising edge of a clock pulse generated by the first timer 7, as shown in FIG. 2 and FIGS. 6 and 7 (described later). The timing of the change may be the falling edge of the clock pulse from the first timer 7, as shown in FIG. 8, which will be described later.

[0030] The second timer 8 has an oscillator that vibrates at a high frequency (e.g., 250 MHz to 500 MHz), an output unit that outputs clock pulses based on the oscillation of the oscillator, and a counter that counts the number of clock pulses. An example of the oscillator of the second timer 8 is a ring oscillator. The time resolution of the second timer 8 is, for example, 1 to 2 ns. The second timer 8 measures a second time, which is the time from the point in time when an ultrasonic signal transmitted from one ultrasonic transmitter / receiver and received by the other ultrasonic transmitter / receiver is detected by the reception detection means 6 (i.e., the zero-crossing point) to the above-mentioned change timing. Note that the counters may be provided separately and independently in the first timer 7 and the second timer 8.

[0031] The control means 9 controls the operation of the first timer 7 and the second timer 8. Specifically, the control means 9 causes the first timer 7 to start counting when a drive signal is given to one of the ultrasonic transmitter / receivers by the drive means 4 via the switching means 5. The control means 9 also causes the second timer 8 to start counting when an ultrasonic signal transmitted from one ultrasonic transmitter / receiver and received by the other ultrasonic transmitter / receiver is detected by the reception detection means 6. Furthermore, the control means 9 ends the counting by the first timer 7 and the second timer 8 at the timing of the change.

[0032] The calculation means 10 calculates the flow rate of the fluid based on the first time calculated from the count number by the first timer 7 and the second time calculated from the count number by the second timer 8. Specifically, as shown in FIG. 2 , the calculation means 10 obtains the propagation time Tdw of the ultrasonic signal transmitted from the downstream first ultrasonic transmitter / receiver 2, propagated through the fluid, and then received by the upstream second ultrasonic transmitter / receiver 3 by subtracting the second time from the first time in this embodiment. Similarly, the calculation means 10 obtains the propagation time Tup of the ultrasonic signal transmitted from the upstream second ultrasonic transmitter / receiver 3, propagated through the fluid, and then received by the downstream first ultrasonic transmitter / receiver 2 by subtracting the second time from the first time in this embodiment. Note that the propagation time Tdw and the propagation time Tup may be calculated by further subtracting the rise time of the output signal of the receiving ultrasonic transmitter / receiver (the time from the start of output of the output signal to the zero-crossing point) from the result of subtracting the second time from the first time. In the following description, it is assumed that the propagation time Tdw is obtained by subtracting the second time from the first time, and the same applies to the propagation time Tup. In this embodiment, the propagation time Tdw corresponds to the first propagation time or the second propagation time, and the propagation time Tup corresponds to the second propagation time or the first propagation time.

[0033] The calculation means 10 uses the propagation time Tdw and propagation time Tup calculated as described above to calculate the flow rate Q of the fluid according to the following equation 1. Note that the coefficient C in the following equation 1 is a constant.

[0034] (Math. 1) Q=(Tdw-Tup) / (Tdw・Tup)×C

[0035] Next, a description will be given of the count-up by the second timer 8 in one cycle of the clock pulse by the first timer 7. FIG.

[0036] As described above, the second timer 8 has a relatively high time resolution, but the frequency of the clock pulses output based on the oscillation of the oscillator may change depending on the environmental temperature and the like.

[0037] 3, when there is almost no change in the environmental temperature or the like during one cycle of the clock pulse from the first timer 7 (the time interval from the rising edge of the clock pulse to the next rising edge), the time interval CU1 of the count-up by the second timer 8 is set to 1 / 16 of one cycle of the clock pulse from the first timer 7. In this case, the 16th count-up by the second timer 8 is positioned at the end of one cycle of the clock pulse from the first timer 7.

[0038] On the other hand, if there is a change in the environmental temperature or the like, the count-up time interval CU2 by the second timer 8 may be shorter than the time interval CU1. In other words, the number of clock pulses output by the second timer 8 when there is a change in the environmental temperature or the like is greater than the number of clock pulses output by the second timer 8 when there is no change in the environmental temperature or the like. In the example of FIG. 3 , the normalization error is set to 0.9, and the time interval CU2 based on this normalization error is set to 1 / 16.9. Therefore, when there is a change in the environmental temperature or the like, the number of clock pulses counted by the second timer 8 increases by up to, for example, one count compared to the number of counts when there is no change in the environmental temperature or the like. In the example of FIG. 3 , the number of clock pulses counted by the second timer 8 during one cycle of the clock pulses by the first timer 7 is 17. Therefore, as the count increases, the second time measured by the second timer 8 becomes longer. As a result, when the calculation means 10 calculates the propagation times Tdw and Tup, a larger second time may be subtracted from the first time. The propagation time calculated under the influence of this phenomenon will be explained below.

[0039] Fig. 4(a) is a diagram showing the relationship between the calculated propagation time and the actual propagation time when there is no normalization error, and Fig. 4(b) is a diagram showing the relationship between the calculated propagation time and the actual propagation time when there is a normalization error. Fig. 5 is a diagram showing the change in flow rate calculated based on the calculated propagation time in Fig. 4(b). The calculated propagation time shown in Fig. 5 is the propagation time Tdw or the propagation time Tup calculated by the calculation means 10.

[0040] As shown in Figure 4(a), the calculated propagation time without normalization error is approximately equal to the actual propagation time. In contrast, the calculated propagation time with normalization error does not match the actual propagation time. In this case, as shown in Figure 4(b), the actual propagation time indicated by the thin solid line is continuous, while the calculated propagation time with normalization error indicated by the thick solid line is discontinuous. The discontinuous portion occurs because, as described above, a larger second time is subtracted from the first time as the count by the second timer 8 increases, and appears every cycle of the clock pulse by the first timer 7.

[0041] When the discontinuous portion occurs in the calculated propagation time in this way, a local drop occurs in the elapsed time corresponding to the time when the discontinuous portion occurs in the calculated flow rate, as shown in FIG.

[0042] 5, the propagation time calculated when an ultrasonic signal is transmitted from the upstream second ultrasonic transmitter / receiver 3 is t1, and the propagation time calculated when an ultrasonic signal is transmitted from the downstream first ultrasonic transmitter / receiver 2 is t2 (>t1). In this case, the propagation time t1 and the propagation time t2 exist on clock pulses of the same cycle among the clock pulses generated by the first timer 7. Therefore, in view of FIG. 3 and the above-mentioned Equation 1, which has (Tdw-Tup) as its numerator, the normalization error included in (t2-t1), which corresponds to (Tdw-Tup), is relatively small.

[0043] In contrast, in FIG. 5 , the calculated propagation time in the mode in which an ultrasonic signal is transmitted from the second ultrasonic transmitter / receiver 3 on the upstream side is designated as t3. Meanwhile, the propagation time in the mode in which an ultrasonic signal is transmitted from the first ultrasonic transmitter / receiver 2 on the downstream side, which corresponds to a clock pulse different from the clock pulse generated by the first timer 7 corresponding to propagation time t3, is designated as t4 (<t3). That is, propagation time t3 and propagation time t4 do not exist on clock pulses of the same period among the clock pulses generated by the first timer 7. Therefore, in view of FIG. 3 and the above-described Equation 1 having (Tdw-Tup) as the numerator, the normalization error included in the second time in this mode is larger than that in the above-described mode in which an ultrasonic signal is transmitted from the second ultrasonic transmitter / receiver 3 on the upstream side. As a result, the normalization error included in (t4-t3), which corresponds to (Tdw-Tup), is relatively large.

[0044] Therefore, in order to make the second time used in calculating the propagation time Tdw and the second time used in calculating the propagation time Tup have substantially the same value, a process is executed to prevent the propagation time Tdw and the propagation time Tup from corresponding to the time before and after the count-up timing of the clock pulse by the first timer 7. This will be explained in detail below.

[0045] Fig. 6(a) is a diagram showing the time measured by the second timer 8 when a drive signal is transmitted to the upstream second ultrasonic transmitter / receiver 3 at the rising edge Tc1 of the clock pulse generated by the first timer 7, and Fig. 6(b) is a diagram showing the time measured by the second timer 8 when a drive signal is transmitted to the downstream first ultrasonic transmitter / receiver 2 at the rising edge Tc1 of the clock pulse generated by the first timer 7. Fig. 7(a) is a diagram showing the time measured by the second timer 8 when a drive signal is transmitted to the upstream second ultrasonic transmitter / receiver 3 at the falling edge Tc2 of the clock pulse generated by the first timer 7, and Fig. 7(b) is a diagram showing the time measured by the second timer 8 when a drive signal is transmitted to the downstream first ultrasonic transmitter / receiver 2 at the falling edge Tc2 of the clock pulse generated by the first timer 7. Furthermore, Figure 8(a) is a diagram showing the time measured by the second timer 8 when the counting by the second timer 8 is stopped at the falling edge Tc2 of the clock pulse by the first timer 7 when a drive signal is sent to the second ultrasonic transmitter / receiver 3 on the upstream side, and Figure 8(b) is a diagram showing the time measured by the second timer 8 when the counting by the second timer 8 is stopped at the falling edge Tc2 of the clock pulse by the first timer 7 when a drive signal is sent to the first ultrasonic transmitter / receiver 2 on the downstream side.

[0046] When an ultrasonic signal traveling from the upstream second ultrasonic transmitter / receiver 3 to the downstream first ultrasonic transmitter / receiver 2 is transmitted at the rising edge Tc1 of the clock pulse by the first timer 7, and when the end of the propagation time Tup in this case corresponds to the time before and after the count-up timing of the clock pulse by the first timer 7, the second time Th measured by the second timer 8 may be shortened as shown in Figure 6(a). When the second time Th is shortened in this way, the normalized error described in Figure 3 may be minimized. In this case, the second time Th including the error may be minimized.

[0047] Furthermore, when an ultrasonic signal traveling from the first ultrasonic transmitter / receiver 2 on the downstream side to the second ultrasonic transmitter / receiver 3 on the upstream side is transmitted at the rising edge Tc1 of the clock pulse by the first timer 7, and the end of the propagation time Tdw in this case corresponds to the time before and after the count-up timing of the clock pulse by the first timer 7, the second time Th measured by the second timer 8 may be long, as shown in Figure 6(b). When the second time Th is long in this way, the normalized error may reach its maximum value. In this case, the second time Th including the error may reach its maximum value.

[0048] Considering the above-mentioned Equation 1, which has (Tdw-Tup) as its numerator, the normalization error in the numerator of Equation 1 reaches its maximum value when the calculated flow rate is equal to or less than a threshold value and the second time Th is short or long as described above. In other words, the normalization error in the numerator of Equation 1 reaches its maximum value when the following conditions are met: the difference between the propagation time Tdw and the propagation time Tup is equal to or less than a threshold value; and the number of clock pulses from the second timer 8 included in one cycle of the clock pulses from the first timer 7 is equal to or less than a threshold value (in other words, the ratio of the second time measured by the second timer 8 to the first time measured by the first timer 7 is equal to or less than a first predetermined value); or the number of clock pulses from the second timer 8 included in the one cycle is equal to or greater than a threshold value (in other words, the ratio of the second time to the first time is equal to or greater than a second predetermined value) (hereinafter, these are referred to as processing conditions). As a result, the accuracy of the flow rate calculation is significantly reduced. The above threshold values ​​are set in advance. The first predetermined value is exemplified as 10 to 20%, and the second predetermined value is exemplified as 80 to 90%. However, the first predetermined value and the second predetermined value are not limited to the above values ​​and can be changed as appropriate.

[0049] Therefore, the driving means 4 performs processing to change the timing of transmission of a driving signal based on a clock pulse from the first timer 7 to one of the first ultrasonic transmitter / receiver 2 and the second ultrasonic transmitter / receiver 3 by a predetermined time when the above processing conditions are satisfied, from the same transmission timing when the above processing conditions are not satisfied.

[0050] Specifically, the driving means 4 performs processing so that the transmission timing of the drive signal is not the rising edge Tc1 of the clock pulse from the first timer 7, but the falling edge Tc2, as shown in both Figures 7(a) and 7(b). In other words, the transmission timing is shifted by half of one cycle of the clock pulse from the first timer 7. As a result, as shown in both Figures 7(a) and 7(b), the respective second times Th take approximately the same value. Therefore, the error in the propagation time Tdw and the error in the propagation time Tup are approximately canceled out by (Tdw-Tup), which is one calculation part of the above-mentioned equation 1 used when calculating the flow rate. This improves the calculation accuracy of the flow rate.

[0051] Alternatively, the control means 9 executes a process of changing the timing of stopping the second timer 8 based on the clock pulse from the first timer 7 when the processing conditions are satisfied, and the timing of stopping the second timer 8 when the processing conditions are not satisfied, by a predetermined time.

[0052] Specifically, the control means 9 stops the second timer 8 not at the rising edge Tc1 of the clock pulse from the first timer 7 (the rising edge Tc1 after the zero-crossing point), but at the falling edge Tc2 (the falling edge Tc2 after the zero-crossing point), as shown in both FIGS. 8(a) and 8(b). In other words, the stop timing is shifted by half of one cycle of the clock pulse from the first timer 7. This process also results in the second times Th being approximately equal, as shown in both FIGS. 8(a) and 8(b), similar to the above-described FIGS. 7(a) and 7(b). Therefore, the error in the propagation time Tdw and the error in the propagation time Tup are almost canceled out by (Tdw-Tup), which is one calculation part of the above-described Equation 1 used when calculating the flow rate. This improves the accuracy of the flow rate calculation.

[0053] As described above, according to the flow measurement device 100 of this embodiment, when the processing condition is satisfied, the drive unit 4 shifts the transmission timing of the drive signal based on the clock pulse from the first timer 7 by a predetermined time relative to the transmission timing when the processing condition is not satisfied. Alternatively, when the processing condition is satisfied, the control unit 9 shifts the stop timing of the second timer 8 based on the clock pulse from the first timer 7 by a predetermined time relative to the stop timing when the processing condition is not satisfied. This allows the second time used to calculate the propagation time Tdw and the second time used to calculate the propagation time Tup to be approximately equal. Therefore, when calculating the flow rate using the above-mentioned Equation 1, errors in the propagation time Tdw and the propagation time Tup are approximately canceled out. This improves the accuracy of the flow rate calculation.

[0054] The present disclosure is not limited to the above-described embodiment, and various modifications are possible without departing from the spirit of the present disclosure. For example, the following modifications are possible.

[0055] In the above embodiment, the process of shifting the timing of transmitting the drive signal by the drive means 4 and the process of shifting the timing of stopping the second timer 8 by the control means 9 are performed separately and independently, but this is not limited to this. The process of shifting the timing of transmitting the drive signal by the drive means 4 and the process of shifting the timing of stopping the second timer 8 by the control means 9 may be performed together. In this case as well, the same effect as described above can be achieved.

[0056] Furthermore, in the above embodiment, the timing of transmitting the drive signal by the drive means 4 is shifted by half of one cycle of the clock pulse from the first timer 7, but this is not limited to this, and the amount of shift in the transmission timing relative to one cycle of the clock pulse from the first timer 7 can be set as appropriate.

[0057] In addition, in the above embodiment, the stop timing of the second timer 8 by the control means 9 is shifted by 1 / 2 of one cycle of the clock pulse from the first timer 7, but this is not limited to this, and the amount of shift in the stop timing relative to one cycle of the clock pulse from the first timer 7 can be set as appropriate.

[0058] REFERENCE SIGNS LIST 1 Measurement flow path 2 First ultrasonic transmitter / receiver 3 Second ultrasonic transmitter / receiver 4 Driving means 5 Switching means 6 Reception detection means 7 First timer 8 Second timer 9 Control means 10 Calculation means 100 Flow rate measuring device Tc1 Rising time of clock pulse by first timer Tc2 Falling time of clock pulse by first timer

Claims

1. A first ultrasonic transmitter / receiver and a second ultrasonic transmitter / receiver that are provided in a measurement flow path and transmit and receive ultrasonic signals; a drive means that transmits a drive signal to the first ultrasonic transmitter / receiver or the second ultrasonic transmitter / receiver; a reception detection means that detects the ultrasonic signal transmitted from one of the first ultrasonic transmitter / receiver and the second ultrasonic transmitter / receiver in response to the drive signal and received by the other ultrasonic transmitter / receiver; a first timer that outputs clock pulses at a predetermined cycle and counts the clock pulses, measuring a first time period that is the time from when the ultrasonic signal is transmitted from one of the ultrasonic transmitter / receivers to when the value of the clock pulse changes after a predetermined condition is satisfied; a second timer that outputs clock pulses at a predetermined cycle and counts the clock pulses, measuring a second time period that is the time from when the ultrasonic signal transmitted from one of the ultrasonic transmitter / receivers and received by the other ultrasonic transmitter / receiver is detected by the reception detection means to when the change occurs; and a control means that controls the operation of the first timer and the operation of the second timer. a calculation means for calculating a flow rate of a fluid based on a first propagation time obtained based on the first time and the second time in a mode in which an ultrasonic signal is transmitted from one ultrasonic transmitter / receiver to the other ultrasonic transmitter / receiver, and a second propagation time obtained based on the first time and the second time in a mode in which an ultrasonic signal is transmitted from the other ultrasonic transmitter / receiver to the one ultrasonic transmitter / receiver, wherein the drive means transmits the drive signal based on a clock pulse output by the first timer, and the transmission timing of the drive signal when the flow rate calculated by the calculation means is equal to or less than a threshold value differs by a predetermined time from the transmission timing when the flow rate exceeds the threshold value.

2. A first ultrasonic transmitter / receiver and a second ultrasonic transmitter / receiver that are provided in the measurement flow path and transmit and receive ultrasonic signals; a drive means that transmits a drive signal to the first ultrasonic transmitter / receiver or the second ultrasonic transmitter / receiver; a reception detection means that detects the ultrasonic signal transmitted from one of the first ultrasonic transmitter / receiver and the second ultrasonic transmitter / receiver in response to the drive signal and received by the other ultrasonic transmitter / receiver; a first timer that outputs clock pulses at a predetermined cycle and counts the clock pulses, measuring a first time period that is the time from when the ultrasonic signal is transmitted from one of the ultrasonic transmitter / receivers to when the value of the clock pulse changes after satisfying a predetermined condition; a second timer that outputs clock pulses at a predetermined cycle and counts the clock pulses, measuring a second time period that is the time from when the ultrasonic signal transmitted from one of the ultrasonic transmitter / receivers and received by the other ultrasonic transmitter / receiver is detected by the reception detection means to when the change occurs; and a control means that controls the operation of the first timer and the operation of the second timer. a calculation means for calculating a flow rate of a fluid based on a first propagation time obtained based on the first time and the second time in a mode in which an ultrasonic signal is transmitted from one ultrasonic transmitter / receiver to the other ultrasonic transmitter / receiver, and a second propagation time obtained based on the first time and the second time in a mode in which an ultrasonic signal is transmitted from the other ultrasonic transmitter / receiver to the one ultrasonic transmitter / receiver, wherein the control means stops the timekeeping by the second timer based on a clock pulse output by the first timer, and differentiates by a predetermined time the stop timing of the second timer when the flow rate calculated by the calculation means is equal to or less than a threshold value and the stop timing when the flow rate exceeds the threshold value.

3. A flow rate measuring device according to claim 1 or 2, wherein the predetermined time is half the time of one cycle of the clock pulse output by the first timer.

4. The flow rate measuring device according to claim 1, wherein the driving means, when the ratio of the second time measured by the second timer to the first time measured by the first timer is equal to or less than a first predetermined value or the ratio of the second time to the first time is equal to or greater than a second predetermined value, differentiates by a predetermined time the transmission timing of the drive signal when the ratio of the second time to the first time is equal to or less than the first predetermined value or the ratio of the second time to the first time is equal to or greater than the second predetermined value from the transmission timing when the ratio of the second time to the first time exceeds the first predetermined value or the ratio of the second time to the first time is less than the second predetermined value.

5. The flow rate measuring device according to claim 2, wherein the driving means, when the ratio of the second time measured by the second timer to the first time measured by the first timer is equal to or less than a first predetermined value or the ratio of the second time to the first time is equal to or greater than a second predetermined value, differentiates by a predetermined time the stop timing of the second timer when the ratio of the second time to the first time is equal to or less than the first predetermined value or the ratio of the second time to the first time is equal to or greater than the second predetermined value from the stop timing when the ratio of the second time to the first time exceeds the first predetermined value or the ratio of the second time to the first time is less than the second predetermined value.

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