JP2012127677A - Ultrasonic flow rate measurement device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an ultrasonic flow rate measurement device for saving energy while maintaining its flow rate measurement accuracy.SOLUTION: An ultrasonic flow rate measurement device 1 includes a pair of ultrasonic transducers 3, 4 arranged in a measurement channel 2, a changeover section 5, a transmitting section 6, a receiving section 7, a propagation time measurement section 8, a flow rate calculation section 9, and an impedance change section 7a, and the impedance change section 7a is configured so as to change an input impedance Z of the receiving section 7 for increase in a range in which the proportion of errors to the calculated flow rate falls within a predetermined allowable value.

Description

  The present invention relates to an ultrasonic flow measuring device that measures a flow rate of a fluid supplied from a gas supply source through a flow path using an ultrasonic transducer.

  Conventionally, for example, when measuring the flow rate of a fluid such as a gas flowing in a gas pipe, a measuring device using an ultrasonic transducer has been used. In this measuring apparatus, an ultrasonic transducer is arranged in a pair on the upstream side and the downstream side of the gas pipe, and the ultrasonic wave emitted from one ultrasonic transducer is sent to the other ultrasonic transducer. To receive. Further, by switching the pair of ultrasonic transducers between the reception side and the transmission side, ultrasonic waves are respectively generated in the forward direction (the direction from the upstream side to the downstream side) and the reverse direction with respect to the gas flow. Is measured, and the flow rate is measured from the measured value.

  By the way, in the case of such an ultrasonic flow measuring device, generally, a receiving unit is provided to amplify the ultrasonic wave received by the ultrasonic transducer on the receiving side. There is an input impedance specific to the circuit to be constructed. An interelectrode capacitance necessarily exists between the pair of ultrasonic transducers. Therefore, a measurement error depending on the input impedance and the capacitance between the electrodes occurs in the conventional ultrasonic flow measurement device. And the technical thought which improves the measurement accuracy of flow volume is proposed irrespective of this measurement error (refer to patent documents 1).

  In the measuring device disclosed in Patent Document 1, a low input unit that receives the output of the ultrasonic transducer on the receiving side is provided, and the low impedance is low due to the relationship between the input impedance of the low input unit and the internal impedance of the ultrasonic transducer. The input impedance of the input section is optimized. Specifically, the input impedance of the low input unit is set to be smaller than the internal impedance of the ultrasonic transducer.

Japanese Patent No. 3585476

  However, since the measurement accuracy of the flow rate varies depending on the type of fluid to be measured such as gas, it is not necessarily optimal because of the relationship between the input impedance of the low input part and the internal impedance of the ultrasonic transducer. It's not even a value. In addition, since the input impedance also becomes a determinant of power consumption, as a practical problem, when determining the input impedance, the viewpoint of energy saving cannot be ignored.

  Therefore, in view of the circumstances as described above, an object of the present invention is to provide an ultrasonic flow measuring device that can save energy while maintaining flow measurement accuracy.

  An ultrasonic flow measuring device according to the present invention is disposed on the upstream side and the downstream side in a flow path through which a fluid to be measured flows, and a pair of ultrasonic transducers for measuring the flow rate of the fluid to be measured, A pair of ultrasonic transducers are received by a switching unit that switches between a transmission side and a reception side, a transmission unit that drives the ultrasonic transducer on the transmission side to generate ultrasonic waves, and an ultrasonic transducer on the reception side A reception unit that amplifies ultrasonic waves, a propagation time measurement unit that measures the propagation time of ultrasonic waves until ultrasonic waves from the ultrasonic transducer on the transmission side are received by the ultrasonic transducer on the reception side, and measured propagation A flow rate calculation unit that calculates a flow rate of the fluid to be measured based on time, and an impedance change unit that varies an input impedance of the reception unit, wherein the impedance change unit has a predetermined error rate with respect to the calculated flow rate. Range included in tolerance In is configured to change so as to increase the input impedance of the receiver.

  By adopting such a configuration, it is possible to save energy by increasing the input impedance while keeping the flow rate measurement accuracy at a certain level or higher. In an ultrasonic flow measuring device, generally, as the input impedance increases, the flow measurement error (in other words, the measurement error of the ultrasonic propagation time) increases, but the power consumption tends to decrease. .

  The impedance changing unit may be configured to change the input impedance according to the type of the fluid to be measured. By adopting such a configuration, it is possible to save energy while maintaining the measurement accuracy (ratio of error with respect to the measured flow rate) that varies depending on the type of fluid to be measured above a certain level by changing the input impedance.

  Further, the impedance changing unit may be configured to increase the input impedance as the sound velocity in the fluid to be measured is lower. Generally, the measurement error of the flow rate tends to be smaller as the fluid to be measured has a lower sound speed. Therefore, in such a case, by increasing the input impedance, further energy saving can be achieved while the measurement accuracy is somewhat lowered within the allowable range.

  The impedance change unit may be configured to increase the input impedance as the flow rate calculated by the flow rate calculation unit increases. Generally, the influence of measurement error tends to decrease as the flow rate of the fluid to be measured increases. Therefore, in such a case, by further increasing the input impedance, further energy saving can be achieved while the measurement accuracy is somewhat lowered within the allowable range.

  According to the present invention, it is possible to provide an ultrasonic flow measuring device capable of saving energy while maintaining flow measuring accuracy.

It is a schematic diagram which shows the flow volume measuring apparatus which concerns on this Embodiment. It is a typical graph for demonstrating the process which changes the input impedance Z.

  Hereinafter, an ultrasonic flow measuring device (hereinafter simply referred to as “flow measuring device”) according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a schematic diagram showing a flow rate measuring apparatus according to the present embodiment. As shown in FIG. 1, the flow rate measuring device 1 includes a pair of ultrasonic transducers 3 and 4 provided in a measurement channel 2, and one ultrasonic transducer 3 is provided in the measurement channel 2. Is disposed on the upstream side of the other ultrasonic transducer 4 with respect to the flow direction of the fluid to be measured. In the example shown in FIG. 1, a pair of ultrasonic transducers 3 and 4 are arranged so as to sandwich the measurement flow path 2, but the present invention is not limited to this. For example, the ultrasonic transducers 3 and 4 are arranged on the same side with respect to the measurement flow path 2, and the ultrasonic waves from one ultrasonic transducer are reflected on the inner wall of the measurement flow path 2 and the other ultrasonic wave is reflected. You may comprise so that it may receive with a sound wave vibrator.

  Further, the flow rate measuring device 1 includes a switching unit 5, a transmission unit 6, and a reception unit 7. Of these, the switching unit 5 switches the ultrasonic transducers 3 and 4 between the transmission side and the reception side at a predetermined timing. The transmission unit 6 is connected to the ultrasonic transducer on the transmission side among the ultrasonic transducers 3 and 4 via the switching unit 5 and drives the ultrasonic transducer to generate ultrasonic waves. The receiving unit 7 is connected to the receiving-side ultrasonic transducer via the switching unit 5, and amplifies a signal input from the ultrasonic transducer via the switching unit 5.

  Here, an impedance changing unit 7a is provided in the receiving unit 7 described above. The impedance changing unit 7a can be composed of a coil and a resistor, and makes the input impedance (Z) of the receiving unit 7 variable.

  In addition, a propagation time measurement unit 8 is connected to the reception unit 7, and a flow rate calculation unit 9 is connected to the propagation time measurement unit 8. The propagation time measuring unit 8 measures the propagation time of the ultrasonic wave between the ultrasonic transducers 3 and 4 based on the received signal at the receiving unit 7. Based on the measured propagation time, the flow rate calculation unit 9 performs an operation taking into account other parameters such as the distance between the ultrasonic transducers 3 and 4 and the temperature in the measurement flow path 2 to determine the fluid to be measured. Calculate the flow rate.

  Further, the flow rate measuring device 1 includes a control unit 10. The control unit 10 can be configured by a processor, a logic circuit, or the like. The switching unit 5, the transmission unit 6, the reception unit 7 (and the impedance change unit 7 a), the propagation time measurement unit 8, and the flow rate calculation unit 9 described above. Control each action.

  In such a flow rate measuring apparatus 1 according to the present embodiment, the impedance changing unit 7a changes the input impedance Z of the receiving unit 7 in accordance with the type of fluid to be measured, the sound speed, the measured flow rate, and the like. Yes. Below, the principle of the process which changes this input impedance Z is demonstrated. Such processing is realized by the control unit 10 controlling the impedance changing unit 7a.

  FIG. 2 is a schematic graph for explaining a process of changing the input impedance Z. In FIG. 2, the horizontal axis represents the input impedance Z, the upward positive vertical axis intersecting the horizontal axis represents the measured flow error ΔQ, and the downward positive vertical axis represents the flow rate measurement apparatus 1. The consumption current I is shown. First, the flow rate of the fluid to be measured that is measured by the flow rate measuring device 1 can be calculated by the following equation (1).

  Here, Q in equation (1) is the measured flow rate, T1 is the propagation time of the ultrasonic wave traveling in the reverse direction (ultrasonic wave traveling from the ultrasonic transducer 4 to the ultrasonic transducer 3), and T2 is the ultrasonic wave traveling in the forward direction. The propagation time of the sound wave, α is a measurement error of the propagation time, and C is a constant.

  As can be seen from this equation (1), when the flow rate of the fluid to be measured actually passed through the measurement channel 2 is zero, theoretically, T1 and T2 have the same value, so the flow rate Q should also be zero. is there. However, due to the capacitance between the electrodes of the ultrasonic transducers 3 and 4 and the input impedance Z of the receiving unit 7, a measurement error indicated by α in Equation (1) occurs. Therefore, a constant flow rate error ΔQ is measured even at zero flow rate. Therefore, in the flow rate measuring apparatus 1 according to the present embodiment, a predetermined threshold value ΔQmax is set as the allowable upper limit value of the flow rate error ΔQ (see FIG. 2).

The upper graph of Figure 2, a graph showing the relationship between the input impedance Z and the flow rate error Delta] Q, and functions f _A a gas A, exemplifies the function f _B about sonic velocity is lower gas B than the gas A Yes. As can be seen from the functions f _A and f _B , the relationship between the input impedance Z and the flow rate error ΔQ tends to increase as the input impedance Z increases. Therefore, in order to reduce the flow rate error ΔQ, it is preferable to make the input impedance Z as small as possible.

  In FIG. 2, for gas A, the input impedance when the flow rate error ΔQ becomes the upper limit value ΔQmax is Z1, and for gas B, the input impedance when the flow rate error ΔQ becomes the upper limit value ΔQmax is Z2 ( > Z1). Furthermore, when the input impedance is Z1, the flow rate error when measuring gas B as the fluid to be measured is ΔQ1 (<ΔQmax). When this is seen from the magnitude relationship between the sound speeds, it can be seen that the smaller the sound speed (the more the fluid to be measured has a longer propagation time), the smaller the flow rate error ΔQ. This can also be understood from the fact that the influence of the numerator error α on the flow rate Q becomes relatively small as a result of the increase in the values of T1 and T2 as the propagation time becomes longer in Equation (1).

  On the other hand, the lower graph of FIG. 2 shows the relationship between the input impedance Z and the current consumption I. As shown in FIG. 2, regardless of the type of fluid to be measured (gas A, B), this relationship tends to decrease the current consumption I as the input impedance Z increases. Therefore, from the viewpoint of energy saving, it is preferable to increase the input impedance Z in order to reduce the consumption current I as much as possible.

  Therefore, if the input impedance Z is fixed to Z1 and the fluid to be measured flowing in the measurement flow path 2 is changed from the gas A to the gas B, the flow path error becomes ΔQ1, and the flow rate error becomes the upper limit value ΔQmax. On the other hand, there is a margin of (ΔQmax−ΔQ1). Therefore, when the flow rate measuring device 1 according to the present embodiment is changed to the gas B, the flow rate error ΔQ is increased within a range not exceeding the allowable upper limit value ΔQmax, thereby reducing the current consumption I and saving energy. It is going to plan. For example, in the above case, the input impedance can be increased from Z1 to Z2.

  As described above, the flow rate measuring device 1 according to the present embodiment has a value as large as possible within the range included in the predetermined allowable value for the input impedance Z according to the type of fluid to be measured. By changing, it is possible to save energy while maintaining the measurement accuracy of the flow rate (the ratio of the flow rate error to the measured flow rate). Note that, as the type of fluid to be measured, attention can be paid to the difference in sound velocity that propagates through the fluid to be measured, such as the gases A and B described above. That is, the input impedance Z can be changed so that the fluid to be measured (eg, gas B) having a low propagation velocity is larger than the fluid to be measured (eg, gas A) having a high sound propagation velocity. .

  By the way, in the above description, the process of changing the input impedance Z according to the type of the fluid to be measured has been described assuming that the flow rate of the fluid to be measured is zero (T1 = T2 in Expression (1)). That is, among the graphs shown in FIG. 2, the graph relating to the upper flow rate error ΔQ shows a tendency when the flow rate is zero. However, as described above, the measurement accuracy of the flow rate is represented by the ratio of the flow rate error to the measured flow rate. Therefore, even if the flow rate error when measuring a non-zero flow rate exceeds the flow rate error ΔQmax at zero flow rate, if the measurement accuracy is within the allowable range as a result, there is a problem from the viewpoint of measurement accuracy. There is no.

  That is, in Formula (1), the difference (T1-T2) between reverse propagation time T1 and forward propagation time T2 increases as the flow rate increases. For this reason, the influence of the measurement error α of the propagation time on the flow rate Q is reduced. Therefore, when the flow rate is increased, the measurement error α of the propagation time can be increased within a predetermined allowable range desired as measurement accuracy. In other words, this means that the flow rate error ΔQmax can be increased, and this is synonymous with the fact that the input impedance Z can be increased.

  Therefore, the flow rate measuring device 1 according to the present embodiment maintains the flow rate measurement accuracy by changing the input impedance Z so as to increase as the flow rate Q increases, based on the measurement result of the flow rate Q. Further energy saving is planned.

  The present invention can be applied to an ultrasonic flow measurement device capable of saving energy while maintaining flow measurement accuracy.

DESCRIPTION OF SYMBOLS 1 Ultrasonic flow measuring device 2 Measurement flow path 3 Ultrasonic vibrator 4 Ultrasonic vibrator 5 Switching part 6 Transmitting part 7 Receiving part 7a Impedance changing part 8 Propagation time measuring part 9 Flow rate calculating part 10 Control part

Claims (4)

A pair of ultrasonic transducers disposed on the upstream side and the downstream side in the flow path through which the fluid to be measured flows, for measuring the flow rate of the fluid to be measured;
A switching unit for switching the pair of ultrasonic transducers between a transmission side and a reception side;
A transmitter that generates ultrasonic waves by driving the ultrasonic transducer on the transmission side;
A receiver for amplifying the ultrasonic wave received by the ultrasonic transducer on the receiving side;
A propagation time measurement unit that measures the propagation time of the ultrasonic wave until the ultrasonic wave from the ultrasonic transducer on the transmission side is received by the ultrasonic transducer on the reception side;
A flow rate calculation unit that calculates the flow rate of the fluid to be measured based on the measured propagation time; and an impedance change unit that makes the input impedance of the reception unit variable.
The ultrasonic type, wherein the impedance changing unit is configured to change so as to increase the input impedance of the receiving unit within a range in which a ratio of an error to the calculated flow rate is included in a predetermined allowable value. Flow measurement device.   The ultrasonic flow rate measuring apparatus according to claim 1, wherein the impedance changing unit is configured to change the input impedance according to a type of the fluid to be measured.   The ultrasonic flow rate measuring apparatus according to claim 2, wherein the impedance changing unit is configured to increase the input impedance as the speed of sound in the fluid to be measured decreases. The ultrasonic type according to any one of claims 1 to 3, wherein the impedance change unit is configured to increase the input impedance as the flow rate calculated by the flow rate calculation unit increases. Flow measurement device.

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