JP2014224685A - Flow rate measuring device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an ultrasonic flowmeter that is able to accurately measure a propagation time even if distortion occurs in a reception waveform due to influence from vibration noise or the like.SOLUTION: In a flow rate measurement device, variation arithmetic means 16 obtains a difference between a measured time value in a previous unit measuring step and a measured time value in a present unit measuring step obtained by timer means 10. If the difference value is equal to a cycle of a reception signal amplified by amplification means 6, erroneous measurement determination means 17 determines the present measured time value is erroneous, selection means 12 selects only effective values from output of the timer means 10, and propagation time arithmetic means 13 obtains a propagation time using the selected data.

Description

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

  Conventionally, this type of flow rate measuring apparatus is generally as shown in FIG. In FIG. 4, a first transducer 42 that transmits ultrasonic waves and a second transducer 43 that receives ultrasonic waves are arranged in the flow path 41 so as to face each other at an angle θ in the flow direction.

  Further, switching means 44 for switching transmission / reception of the first vibrator 42 and the second vibrator 43, transmission means 45 for outputting a driving signal to the first vibrator 2, and a signal received by the vibrator on the receiving side have a constant amplitude. The amplification means 46 for adjusting the amplification factor, the reference comparison means 47 for comparing the output of the amplification means 46 with a predetermined reference voltage, the voltage setting means 48 for outputting the reference voltage to the reference comparison means 47, and the received signal as the reference The main part is constituted by the determination means 49 that outputs a signal at the first zero cross point after exceeding the voltage.

  FIG. 5 is a time chart for explaining a series of operations from the output of the transmission signal to the detection of the reception signal. As shown in the figure, the signal is transmitted from the transducer set on the transmission side by the drive signal output of the transmission means 45. The received ultrasonic signal is received by the vibrator set on the receiving side, amplified by the amplifying means 46 and output as the received signal A, and the reference comparing means 47 outputs a signal when the received signal A exceeds the reference voltage Vr. C is output, and the determination unit 49 outputs the signal D at the first zero cross point a after the output of the signal C. As described above, the flow from the drive signal output of the transmission means 45 to the output of the signal D of the determination means 49 is a flow of transmission / reception of the ultrasonic signal once.

  Further, it includes a repeating means 50 for counting the number of times of output of the signal D of the judging means 49 and a control means 51 for controlling it. The control means 51 outputs an ultrasonic drive signal to the transmitting means 45 when receiving the signal D. Thus, transmission / reception of ultrasonic signals is resumed. Then, the repeating unit 50 repeats the same operation until the predetermined number of signals D are counted.

  In addition, the time measuring means 52 that measures the time required for a plurality of times of ultrasonic transmission / reception repeated by the repeating means 50, and the flow rate is calculated in consideration of the size of the flow path and the flow state according to the time measured by the time measuring means 52. And a flow rate calculation means 53.

  In the flow rate measuring apparatus configured as described above, first, an ultrasonic signal is transmitted from the first vibrator 42 by the drive signal output from the transmission unit 45. The second transducer 43 receives the ultrasonic signal transmitted from the first transducer 42, and the received signal is amplified by the amplification unit 46, and then output to the reference comparison unit 47 and the determination unit 49. One transmission / reception is completed with the signal D output from the terminal.

  When the predetermined number of transmissions / receptions N is completed by the repeating unit 50, the time measuring unit 52 counts the time required so far. The ultrasonic propagation time measurement from the first transducer 42 arranged on the upstream side of the flow to the second transducer 43 arranged on the downstream side is hereinafter referred to as forward propagation time measurement.

When the propagation time measurement in the forward direction is completed, the control means 51 drives the switching means 44 and connects the first vibrator 42, the amplification means 46, and the second vibrator 43 to the transmission means 45, so that the direction of ultrasonic propagation is reached. N is repeatedly measured in the same manner as before, and the time measuring means 52 counts the required time. Hereinafter, this is referred to as propagation time measurement in the reverse direction of the flow.

  As described above, using the forward propagation time Tu and the backward propagation time Td per time obtained from the measurement result of the forward propagation time of the flow and the measurement result of the reverse propagation time of the flow, The flow rate calculation means 53 obtains the flow rate Q using the following calculation formula.

Q = S × L / 2 cos θ (1 / Tu−1 / Td) (Formula 1)
In (Expression 1), L is a linear distance connecting the central portions of the first vibrator 42 and the second vibrator 43, θ is an angle formed by a straight line connecting both vibrators and the flow direction, and S is a flow path cut-off. It is an area.

  In actual measurement, since the true propagation time is the rising point b of the received waveform shown in FIG. 5, Tu and Td are numerical values including a delay time with respect to the true propagation time. However, if the frequency of the received waveform of the ultrasonic wave is known in advance, it is possible to measure the true propagation time by correcting this delay time. In the actual formula, Tu and Td are not used directly, A value obtained by correcting this delay time is used.

  In such a measurement method, correction based on the delay time is an important factor for ensuring measurement accuracy. Therefore, it is necessary for the determination means 49 to always detect the signal D at the same position of the received waveform. If it is assumed that the output timing of the signal D is shifted by one period in the measurement in the forward direction and the reverse direction, a large measurement error occurs.

  Therefore, in order to always detect the same zero cross point, the control means 51 adjusts the amplification factor of the amplification means 46 to optimize the received waveform. For example, the amplification factor is adjusted by the amplifying unit 46 so that the waveform amplitude is always at the same voltage level before or after the measurement by the repeating unit 50 is started.

  That is, as shown in FIG. 5, a fixed limit range is set for the maximum voltage (the peak voltage of the fifth wave) of the received wave after amplification, and the amplification factor is changed so that the maximum voltage of the received wave falls within this range. Let Specifically, as a reference voltage of a comparator (not shown), an upper limit value and a lower limit value of a limit range are set, and the amplification factor is changed while looking at the comparison result between the reference voltage and the received wave, or a peak hold circuit And a method of reading the voltage held by the peak hold circuit in the AD converter circuit and changing the amplification factor so that this value falls within the limit range.

  Thus, if an appropriate amplification factor is set in the amplification means 46, the maximum voltage of the received waveform (the peak voltage of the fifth wave) is not only kept constant, but also the peak voltage of the first to fourth waves. Is also kept almost constant.

  Actually, the received waveform varies slightly depending on temperature, flow rate, etc., but the received waveform is observed in advance, taking into account the difference in these conditions, and the difference between adjacent peak voltages is relatively large. Set the reference voltage at the position. In FIG. 5, since the peak voltage difference between the second wave and the third wave is large, the reference voltage Vr is determined at an arbitrary point between the two voltages. As long as the peak voltage of the fifth wave does not deviate significantly, the determination means 49 can always output the signal D at the falling zero cross of the third wave.

  As another method, at the time of shipment from the factory, the time difference Δt between the output timings of the signals C and D is measured by the time measuring means 52 while gradually changing the reference voltage from the minimum value to the maximum value. Each peak voltage from the first wave to the fifth wave is estimated from the relationship of the time difference ΔT, and based on the result, the reference voltage is set at the midpoint of the voltage corresponding to the peak voltage of the second wave and the peak voltage of the third wave. A method of setting is also proposed.

  This utilizes the property that ΔT decreases as the reference voltage increases and takes a minimum value when the peak of each wave is reached. By using this property, the voltage at which ΔT reaches the first minimum value becomes the peak voltage of the first wave, and thereafter, the peak voltages from the second wave to the fifth wave can be specified. Therefore, unlike the case where the fixed voltage described above is used as the reference voltage, it is possible to absorb variations between individuals, and it is possible to further improve the measurement reliability.

Japanese Patent No. 3468233

  However, in the conventional configuration, there is a case where the output timing of the signal D output at the zero cross point is shifted by one cycle due to waveform distortion caused by the noise component superimposed on the original received waveform.

  For example, when the peak voltage of the second wave becomes larger than the ideal waveform due to noise and the peak voltage of the second wave exceeds the reference voltage Vr, the signal D is output at the zero cross point of the second wave. As a result, a measurement error for one cycle occurs.

  In such a case, since the flow rate value is obtained after all the repeated measurements are completed, it is difficult to determine the noise generated during the repetition.

  Originally, it is usual to use a bandpass filter or the like so that such noise does not occur, but noise of the same frequency as the ultrasonic reception signal is particularly problematic. As this type of noise, a propagation wave (hereinafter referred to as a housing) that reaches the receiving-side transducer by directly transmitting the vibration of the transducer itself through a solid housing (for example, a flow path in which the transducer is disposed). A propagation wave), or electrical vibration noise generated when the vibrator vibrates due to a slight potential difference applied between the two poles of the vibrator when the vibrator on the receiving side is electrically connected to the amplification means. It is done.

  Since these noises have the same frequency as the received signal, it is impossible to remove them with an electrical filter. The noise remains until the arrival timing of the original received waveform, and the original ideal received waveform is distorted. There is. For this reason, the relative positional relationship between the peak voltages from the first wave to the fifth wave is lost, and the output timing of the signal D is moved forward or backward by one cycle, causing a measurement error.

  An object of the present invention is to solve the above-described conventional problems and to enable accurate calculation of propagation time even when waveform distortion occurs.

  In order to solve the above-described conventional problems, the flow measurement device of the present invention uses the amplification unit to calculate the time value of the previous unit measurement process obtained by the change amount calculation unit and the amount of change of the time measurement value of the current unit measurement process. If it is equal to the period of the amplified received signal, the erroneous measurement determination means determines that the measurement is incorrect, the selection means selects only valid data from the multiple time values obtained by the time measurement means, and the selected time measurement value is selected. The propagation time calculation means obtains the propagation time using. As a result, even when the received waveform is distorted due to the effects of vibration noise and the zero cross timing is measured incorrectly, the propagation time is obtained by correcting the data, so the accurate propagation time can be obtained. It becomes.

  The flow measuring device of the present invention corrects the data to determine the propagation time even when the received waveform is distorted due to the influence of the case propagation wave, electrical vibration noise, etc. Can be measured.

Block diagram of a flow rate measuring device in Embodiment 1 of the present invention Time chart explaining the operation of the device Another time chart explaining the operation of the device Block diagram of a conventional measuring device Time chart explaining the operation of the device

  According to a first aspect of the present invention, there are provided a first transducer and a second transducer that are provided in a flow path and transmit / receive an ultrasonic signal, a switching unit that switches transmission / reception of the first and second transducers, and the first and second transducers. Transmitting means for outputting a driving signal to the vibrator, amplifying means for amplifying the received signals of the first and second vibrators, and a time when the received signal output from the amplifying means exceeds a predetermined reference voltage A reception detection means for outputting a reception detection signal, a zero-cross detection means for outputting a zero-cross detection signal at every zero-cross timing of the reception signal after outputting the signal of the reception detection means, and timing from the transmission start of the transmission means. , Time measuring means for measuring the elapsed time until a plurality of zero cross detection signals output from the zero cross detection means, and a propagation time for calculating the propagation time of the ultrasonic signal based on the time measurement result of the time measuring means The calculation means, the flow rate calculation means for calculating the flow rate based on the calculation result of the propagation time calculation means, and the forward and reverse time measurement by the time measurement means by switching the transmission / reception direction of the first and second vibrators. A pair of time measurement in the forward / reverse direction as a unit measurement step, storage means for storing the output of the time measurement means for each execution of the unit measurement step, and the previous unit measurement step stored in the storage means A change amount calculating means for calculating a difference between the time value of the current time and the time measured value of the current time measuring means, and an erroneous measurement for determining an erroneous measurement if the difference calculated by the change amount calculating means is equal to the period of the received signal Determining means, and selecting means for selecting an effective time value excluding the time value determined as erroneous measurement by the erroneous measurement determination means, and the propagation time calculation means is configured to select the time value selected by the selection means. Use to find the propagation time By was formed, even if the strain is timed incorrectly cross detection time occurs in the received waveform by the influence such as vibration noise, it is possible to obtain an accurate travel time by correcting the results.

  The second invention is particularly configured so that the erroneous measurement determination means of the first invention performs erroneous measurement determination by comparing the total values of the forward and reverse bidirectional time values measured in the unit measurement process. Since it is possible to select a change in propagation time due to fluctuations and a time change due to waveform distortion, determination of erroneous measurement can be performed accurately, and flow measurement with higher reliability can be achieved.

(Embodiment 1)
FIG. 1 is a block diagram of a flow rate measuring apparatus according to the first embodiment of the present invention. In FIG. 1, a first vibrator 2 that transmits an ultrasonic signal and a second vibrator 3 that receives an ultrasonic signal are disposed in the flow path 1 so as to face each other in the flow direction. The first vibrator 2 and the transmission means 5 for outputting a drive signal are connected via the switching means 4 for switching the transmission / reception roles of the first vibrator 2 and the second vibrator 3, and the second vibrator 3 receives the signal. Amplifying means 6 for amplifying the signal is connected.

  The reception signal amplified by the amplification means 6 is compared with the reference voltage output from the voltage setting means 8 by the reception detection means 7, and when the reception signal becomes larger, the reception detection signal is output to the zero cross detection means 9.

The zero cross detection means 9 outputs the zero cross detection signal a predetermined number of times for each zero cross timing of the reception signal after the reception detection signal is output. In the present embodiment, this number is described as four times.

  The time measuring means 10 starts time measurement from the drive signal output timing of the transmission means 5 and measures the elapsed time each time the zero cross detection signal is output from the zero cross detection means. That is, four time values are output per transmission / reception.

  These four time values are output to the storage means 11 as the latest time values, and are also output to the selection means 12 for selecting an effective time value. Only the correct data is selected and output to the propagation time calculation means 13.

  The above-described measurement method in which the first vibrator 2 is the transmission side and the second vibrator 3 is the reception side is called forward measurement.

  Next, when the measurement in the forward direction is completed, the control unit 14 outputs a switching signal to the switching unit 4 so as to switch the transmission / reception roles of the two transducers. Two vibrators 3 are connected to the transmission means 5. Then, after the roles of transmission / reception of both vibrators are reversed, the time measuring process similar to the method described above is performed. This is called reverse measurement.

  As described above, the measurement in the forward direction and the backward direction once is referred to as a unit measurement step, and when this unit measurement step is executed a predetermined number of times (32 times in the present embodiment), a propagation time calculation is performed. The means 13 calculates the average propagation times in both forward and reverse directions by summing up the measurement results for every 32 unit measurement steps, and further calculates the flow rate by the flow rate calculation means 15 using the result.

  In addition, each time the unit measurement process ends, the change amount calculation unit 16 calculates the difference between the time measurement value of the previous unit measurement process and the time measurement value of the current unit measurement process stored in the storage unit 11 in both forward and reverse directions. The erroneous measurement determination is performed by the erroneous measurement determination means 17 based on the calculation result by a method described later. When erroneous measurement determination is made by the erroneous measurement determination means 17, valid data is selected by the selection means 12.

  In addition, the control means 14 controls not only the switching means 4 described above but also the overall flow rate measuring device such as the gain set in the amplifying means 6 and the control of the reference voltage output from the voltage setting means 8. It is configured.

  FIG. 2 is a time chart for explaining the operation of the flow rate measuring apparatus. In FIG. 2, the output signal 21 of the transmission means 5, the reception signal 22 amplified by the amplification means 6, the reference voltage 23 which is the output signal of the voltage setting means 8, and the output signal 24 (H / L 2) of the reception detection means 7. Value signal), the time series change of the voltage level of the enable signal 25 (H / L binary signal) output to the zero cross detection means 9 and the output signal 26 (H / L binary signal) of the zero cross detection means 9. Show.

  The horizontal axis is the time axis with the transmission start timing of the output signal 21 of the transmission means 5 as the origin, and the vertical axis is the voltage axis with different origins. However, the reception signal 22 that is the output signal of the amplification means 6 and the reference voltage 23 that is the output signal of the voltage setting means 8 are signals of the same origin. The output of the amplifying means 6 has a voltage signal waveform in which the amplified signal waveform of the ultrasonic reception signal is superimposed on the bias voltage Vb. Further, it is assumed that the reference voltage 23 is set near the midpoint of the peak voltage of the third wave and the peak voltage of the fourth wave of the ideal received waveform.

  The operation and action of the flow rate measuring apparatus configured as described above will be described below.

A rectangular output signal 21 as shown in FIG. 2 is applied from the transmitter 5 to the first vibrator 2.
In the present embodiment, the output signal 21 has a waveform corresponding to three cycles of a frequency of 500 kHz.

  Then, an ultrasonic signal is output from the first vibrator 2 by the output signal 21 and is eventually received by the second vibrator 3. The reception signal received by the second vibrator 3 is amplified by the amplification factor determined by the control means 14 so that the output amplitude from the amplification means 6 becomes constant. The method for determining the amplification factor of the amplifying means 6 is the same as the method described in the background art, and the description thereof is omitted. The reception signal 22 amplified by the amplification means 6 is output to the reception detection means 7 and the zero cross detection means 9.

  The reception detection means 7 is composed of, for example, a comparator and a latch circuit (both not shown). First, a comparison process of the reference voltage 23 and the received signal 22 is executed by the comparator. When the received signal 22 is smaller, the comparator output is H, and when the received signal 22 is larger, the comparator output is L. Become.

  Therefore, the comparator output is H before the reception signal 22 reaches the second vibrator 3. Thereafter, when the received signal 22 exceeds the reference voltage 23, that is, at the point r (Tr on the time axis) where the received signal 22 and the reference voltage 23 first cross, the output of the comparator is inverted to L. This inversion timing corresponds to the reception detection signal. Further, the subsequent output signal 24 maintains the L level by the action of the latch circuit.

  The zero-cross detection means 9 is a comparator that compares the received signal 22 with the bias voltage Vb only when the enable signal 25 is H. The output of the zero-cross detection means 9 is L when the enable signal 25 is L. At time Tr, the output signal 24 of the reception detecting means 7 changes to L, and at the same time, the enable signal 25 is inverted from L to H. At this time, the output signal 26 of the zero cross detecting means 9 is L, but the point is inverted from L to H at the point where the received signal 22 and the bias voltage Vb cross, that is, at the zero cross point a.

  Thereafter, the output signal 26 of the zero cross detection means 9 repeats inversion at the zero cross points b to d of the received signal 22. The inversion timings of these output signals 26 correspond to zero cross detection signals, respectively. When the capture of four predetermined zero cross detection signals is completed, the enable signal 25 becomes L, and thereafter, the output signal 26 of the zero cross detection means 9 maintains L.

  The time measuring means 10 is composed of a timer counter and starts measuring time at the time origin. Each time four zero-cross detection signals detected by the zero-cross detection means 9 are generated, the timekeeping values Ta, Tb, Tc, and Td at that time are temporarily stored in the storage means 11.

  The above is the measurement of the forward direction of the flow. When the forward time measurement is completed, a transmission / reception switching timing signal is output from the control means 14 to the switching means 4. In response to this timing signal, the switching means 4 connects the first vibrator 2 to the amplifying means 6 and the second vibrator 3 to the transmitting means 5 and starts counting in the reverse direction.

  Since the method for determining the zero cross in the reverse direction, the method for measuring each zero cross point, and the method for storing the time value are the same as those for the time measurement in the forward direction described above, the description thereof will be omitted.

  The above-described measurement in which the forward direction and the reverse direction are paired is the unit measurement process, the first unit measurement process is the first measurement process, and the second and third measurement processes are followed by the final 32nd measurement process. The same process is repeated until the process is completed.

Subsequently, with respect to operations after the second measurement step, portions different from the first measurement step will be described. When the first measurement process is finished, the storage means 11 stores the time measurement means 1 in the first measurement process.
Four time-measured values in the forward measurement timed at 0 and four time-measured values in the reverse direction are stored.

  Here, the forward time value corresponding to the first zero cross point a in FIG. 2 is Tau1, the forward time value with respect to the second zero cross point b is Tbu1, hereinafter, the third zero cross time value is Tcu1, and the fourth zero cross. Let Tdu1 be the time measured value. Similarly, the timing results in the reverse direction are Tad1, Tbd1, Tcd1, and Tdd1, in order from the first zero cross. The above is the value stored in the storage unit 11.

  Similarly, the measured values for the zero cross points a, b, c, and d measured by the time measuring means 10 in the forward measurement of the second measuring step are set as Tau2, Tbu2, Tcu2, and Tdu2, respectively. Unlike the first measurement process, after the second measurement process, these time-measured values are subjected to necessary preprocessing before being output to the storage means 11 and the selection means 12.

  First, the change amount calculating means 16 obtains the difference between Tau1 and Tau2, Tbu1 and Tbu2, Tcu1 and Tcu2, and Tdu1 and Tdu2, that is, the value obtained by subtracting the time measurement value of the first measurement process from the time measurement value of the second measurement process. Then, it is determined whether or not the obtained differences are almost equal and the value is a value corresponding to one period of the reception waveform of the vibrator.

  In this embodiment, since the frequency is 500 kHz, the determination value is 2 ± 0.1 or −2 ± 0.1 μs. When the four change amounts obtained by the change amount calculation means 16 are all within the range of the determination value, it is determined that the measurement is incorrect, and the result is transmitted to the selection means 12. The determination value of 2 ± 0.1 μs used here is a value that assumes a case where a large noise signal is superimposed on the received waveform and distortion is generated.

  FIG. 3 is a time chart illustrating an example of a waveform when an erroneous measurement determination is performed. 3 shows an output signal 31 of the transmission means 5, a reception signal 32 amplified by the amplification means 6, a reference voltage 33 of the voltage setting means 8, an output signal (H / L binary signal) 34 of the reception detection means 7, The time series changes of the voltage levels of the enable signal 35 (H / L binary signal) and the output signal 36 (H / L binary signal) of the zero cross detection means 9 output to the zero cross detection means 9 are shown.

  The horizontal axis is the time axis with the transmission start timing of the output signal 31 of the transmission means 5 as the origin, and the vertical axis is the voltage axis with different origins. However, the received signal 32 that is the output of the amplifying means 6 and the reference voltage 33 that is the output signal of the voltage setting means 8 are signals of the same origin. The output of the amplifying means 6 is a voltage signal in which the amplified signal waveform of the ultrasonic reception signal is superimposed on the bias voltage Vb.

  2 and 3 are compared, the output voltage 21 and output signal 31 of the transmission means 5 and the reference voltage 23 and the reference voltage 33 which are output signals of the voltage setting means 8 are the same voltage. On the other hand, the reception signal 22 and the reception signal 32 of the amplifying means 6 have different waveforms, and correspondingly, the output signal 24 and the output signal 34 of the reception detection means 7 and the enable signal 25 and the enable signal output to the zero cross detection means 9 are enabled. The signal 35 and the output signal 26 and the output signal 36 of the zero cross detection means 9 have different waveforms.

  The reception signal 32 of FIG. 3 has 500 kHz vibration noise superimposed on the reception signal 22 of FIG. 2, and in particular, the third wave peak and the fourth wave peak voltage of the reception wave are larger than the reception signal 22 of FIG. . Therefore, the timing at which the received signal 32 exceeds the reference voltage 33 of the voltage setting means 8 is earlier than that in FIG.

Accordingly, the timings at which the outputs of the output signal 34, the enable signal 35, and the output signal 36 change are earlier than those of the output signal 24, the enable signal 25, and the output signal 26 of FIG. Therefore, the first zero cross point a is also faster in FIG. 3 by one period of the received signal than in FIG. 2, and the zero cross points b to d that are the second, third, and fourth zero crosses thereafter are also the same. It is.

  As a result, the four change amounts (the differences between Tau1 and Tau2, Tbu1 and Tbu2, Tcu1 and Tcu2, and Tdu1 and Tdu2) obtained by the change amount calculation means 16 are all in the vicinity of −2 μs, and the erroneous measurement determination means 17 Therefore, the time value obtained by the time measuring means 10 is subjected to necessary post-processing by the selecting means 12.

  The set value of the reference voltage 23 is generally set according to the wave of the received waveform that can take a relatively large noise margin. In the present embodiment, it is set according to the fourth wave, but the temperature, Since the received waveform may be slightly different depending on the environment such as the flow rate, the noise margin may be reduced during the transition period. If vibration noise overlaps with such a situation, the deviation of the zero cross timing is likely to occur.

  Therefore, the selection unit 12 selects valid data from the four time values obtained by the time measuring unit 10 according to the calculation result of the change amount calculating unit 16 when the erroneous measurement determination unit 17 determines that the measurement is incorrect. Select.

  As shown in FIG. 3, when the zero cross points a, b, c, d detected in the second measurement step are shifted one cycle before the first measurement step shown in FIG. The result of the calculation is approximately −2 μs.

  This indicates that the detection point of the zero cross is shifted by one period, so that the data of the shift, that is, the zero cross point a and the zero cross point b in FIG. And zero cross point d as effective data, and the data is transmitted to the propagation time calculation means 13. The propagation time calculation means 13 changes the propagation time calculation method based on the output result of the selection means 12.

  First, the equation for calculating the propagation time when the data is valid is obtained by (Equation 2).

Tx = (Ta + Tb + Tc + Td) /4-4.25T (Formula 2)
Here, T represents the period of the received waveform.

  The physical meaning of the first half of this equation is to calculate the average value of the time measured values of the four zero cross points, that is, the midpoint of the second zero cross point b and the third zero cross point c, that is, the peak time of the fifth wave. Is equal to Since the peak of the fifth wave is at a position delayed by 4.25 cycles from the rising point w of the waveform, the value for 4.25 cycles of the received waveform is subtracted in the latter half of the equation.

  Subsequently, as shown in FIG. 3, the calculation formula when the zero-cross detection timing is shifted by one cycle is as shown in (Formula 3).

Tw = (Tc + Td) /2-3.75T (Formula 3)
The physical meaning of the first half of this equation is the average of the valid time values of the two zero cross points, that is, the midpoint of the third zero cross point c and the fourth zero cross point d, that is, the negative peak of the fourth wave. Equivalent to seeking time. Since the negative peak of the fourth wave is at a position delayed by 3.75 cycles from the waveform rising point w, the value for 3.75 cycles of the received waveform is subtracted in the latter half of the equation.

  Conversely, when the zero-cross detection point is shifted backward by one cycle, it can be obtained by the calculation formula (Formula 4) based on the same concept.

Tx = (Ta + Tb) /2−4.75T (Formula 4)
The physical meaning of the first half of this equation is the average value of the valid time values of the two zero cross points, that is, the midpoint of the first zero cross point a and the second zero cross point b, that is, the negative peak of the fifth wave. Equivalent to seeking time. Since the negative peak of the fifth wave is at a position delayed by 4.75 cycles from the rising point w of the waveform, the value for 4.75 cycles of the received waveform is subtracted in the latter half of the equation.

  As described above, the propagation time can be accurately calculated by using different mathematical expressions according to the amount of change obtained by the amount-of-change calculating means 16.

  In addition, the erroneous measurement determination means 17 uses a method of determining the presence or absence of erroneous measurement based on the total value of the forward and reverse bidirectional measured values in order to increase the reliability of erroneous measurement determination when the flow rate fluctuates.

  For example, when comparing the time measurement values of the first measurement process and the second measurement process, (Formula 5) is used to compare and determine the time measurement value of the first zero cross.

ΔT = (Tau2 + Tad2) − (Tau1 + Tad1) (Formula 5)
This is intended to make an erroneous determination using the property that the total value of both forward and reverse propagation times is constant regardless of the flow rate value in the same environment. It can be determined that it is not a measurement, and the principle will be described below.

  First, the forward propagation time is Tu, the reverse propagation time is Td, the sound velocity is C, the flow velocity is V, the linear distance connecting the center portion of the first vibrator and the second vibrator is L, and both vibrators are connected. When the angle formed by the straight line and the flow direction is θ, it can be expressed by the following equations.

Tu = L / (C + V cos θ) (Expression 6)
Td = L / (C−Vcos θ) (Expression 7)
Here, when C >> V, that is, when the sound velocity C is sufficiently larger than the flow velocity V, (Equation 6) can be approximated as (Equation 8).

Tu = L / C · (1 + V / C cos θ)
≒ L / C · (1-V / Ccosθ) (Equation 8)
Similarly, (Equation 7) can be approximated as (Equation 9).

Td≈L / C · (1 + V / Ccos θ) (Equation 9)
Therefore, the total value of Tu and Td can be expressed by (Equation 10).

Tu + Td = 2L / C (Equation 10)
It can be seen that (Equation 10) is a value independent of the flow velocity V, that is, the flow rate. If this property is used, it is possible to determine erroneous measurement without being affected by fluctuations in propagation time due to flow rate changes.

  That is, based on the principle that the total value of the forward and backward bidirectional time values becomes constant as in (Equation 10), if no erroneous measurement has occurred, the value of ΔT calculated in (Equation 5) Is substantially 0, so that it is possible to prevent a change in propagation time accompanying a change in flow rate from being determined as an erroneous measurement.

For example, it is assumed that the flow velocity actually changes and the change in propagation time corresponding to the change is 1.9 μs in the erroneous measurement range. In this case, if the forward propagation time change is −1.9 μs, the reverse propagation time change is +1.9 μs. Therefore, if it is determined whether or not erroneous measurement is made separately in the forward direction and the reverse direction, it will be determined as erroneous measurement in any direction. According to this method, the value of ΔT obtained by (Equation 5) is Since it is 0, it can be determined that it is not an erroneous measurement.

  When all of the 32 predetermined measurement steps are completed by the method described above, the propagation time calculation means 13 obtains the average propagation time for 32 times in the forward direction and the backward direction, and sets each value as Tu, Let Td.

  When the propagation time calculation means 13 obtains forward and reverse bidirectional propagation times Tu and Td, the flow rate calculation means 15 obtains the fluid flow rate using (Equation 1).

  In this way, the flow rate calculation means 15 calculates the flow rate every time the measurement process is performed a total of 32 times. This series of flows is defined as a unit flow rate calculation step. The control means 14 performs time management of the entire flow rate measuring device so as to execute the unit flow rate calculation step every predetermined time (for example, 2 seconds).

  As described above, the flow rate measuring device according to the present invention can appropriately correct the deviation of the zero-cross detection timing, and can accurately measure the flow rate over a long period of time. Applicable to a wide range of applications. Further, it can be applied to a liquid flow meter such as a water meter.

DESCRIPTION OF SYMBOLS 1 Flow path 2 1st vibrator 3 2nd vibrator 4 Switching means 5 Transmission means 6 Amplification means 7 Reception detection means 8 Voltage setting means 9 Zero cross detection means 10 Time measuring means 11 Storage means 12 Selection means 13 Propagation time calculation means 15 Flow rate Calculation means 16 Change amount calculation means 17 Incorrect measurement determination means

Claims (2)

A first vibrator and a second vibrator which are provided in the flow path and transmit and receive ultrasonic signals;
Switching means for switching between transmission and reception of the first and second vibrators;
Transmitting means for outputting a drive signal to the first and second vibrators;
Amplifying means for amplifying the received signals of the first and second vibrators;
A reception detection means for outputting a reception detection signal when the reception signal output from the amplification means exceeds a predetermined reference voltage;
After the signal output of the reception detection means, zero cross detection means for outputting a zero cross detection signal for each zero cross timing of the reception signal;
Timekeeping means for starting time measurement from the transmission start of the transmission means, and for measuring elapsed times until a plurality of zero cross detection signals output from the zero cross detection means,
Propagation time calculation means for calculating the propagation time of the ultrasonic signal based on the time measurement result of the time measuring means;
Flow rate calculation means for calculating a flow rate based on the calculation result of the propagation time calculation means;
The transmission / reception direction of the first and second vibrators is switched to perform time measurement in the forward direction and in the reverse direction by the time measuring means, and the time measurement in the forward / reverse direction is set as a unit measurement step, and the unit measurement step is executed. Storage means for storing the output of the timing means every time;
Change amount calculating means for calculating a difference between the time value of the previous unit measurement step stored in the storage means and the time value of the current time measuring means;
Erroneous measurement determination means for determining erroneous measurement if the difference calculated by the change amount calculation means is equal to the period of the received signal;
Selecting means for selecting an effective time value excluding the time value determined by the erroneous measurement determination means as an erroneous measurement,
The propagation time calculation means is a flow rate measuring device that obtains propagation time using the time value selected by the selection means. The flow measurement device according to claim 1, wherein the erroneous measurement determination unit performs an erroneous measurement determination by comparing total values of forward and reverse bidirectional time values measured in a unit measurement process.

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