JP2013156075A - Ultrasonic flowmeter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an ultrasonic flowmeter unsusceptible to influences of acoustic noise.SOLUTION: The ultrasonic flowmeter is provided with: at least a pair of ultrasonic echo sounder transducers 2 and 3; a switch part 4 for switching the transmission/reception directions of the ultrasonic echo sounder transducers; a cycle monitoring unit 8 for outputting a cycle abnormality signal when waves outside a prescribed cycle range are detected; and a reception determination unit 9 which determines that detection of a reception point fails when the cycle abnormality signal is inputted, performs detection of the reception point from the beginning with a peak value of the waves from a point of time when the cycle abnormality signal is inputted, and outputs a reception signal when the detection succeeds. Ultrasonic is transmitted more than once in each direction, and in each direction, flow velocity and/or flow rate of a fluid to be measured is calculated on the basis of an average value of a propagation time of ultrasonic whose detection of the reception point has succeeded.

Description

  The present invention relates to an ultrasonic flow meter.

  A pair of ultrasonic transducers (hereinafter also referred to as transducers) are provided on the upstream side and downstream side of the flow path through which the fluid to be measured flows, and the ultrasonic waves from the upstream side to the downstream side between the ultrasonic transducers are provided. There is known an ultrasonic flowmeter that measures the flow rate of a fluid to be measured based on the propagation time of a sound wave and the propagation time of an ultrasonic wave from the downstream side to the upstream side.

  The ultrasonic frequency uses a specific frequency depending on the transducer used. For this reason, when an ultrasonic wave near this frequency comes from outside the ultrasonic flowmeter, it becomes acoustic noise, and the ultrasonic wave cannot be received correctly by the transducer.

  It is known that acoustic noise is generated when there is a flow restriction that causes a large pressure loss. Therefore, conventionally, the ultrasonic flowmeter needs to be installed away from the acoustic noise source, and may not be installed when the distance from the acoustic noise cannot be secured, which has been a weak point of the ultrasonic flowmeter.

Conventionally, a method of mechanically preventing the passage of acoustic noise by providing a strainer or the like in the flow path has been performed (for example, see Patent Document 1).
JP 2004-69528 A

  If a strainer or the like is provided in the flow path as in the prior art, there is a problem in that the pressure loss increases because the flow is inhibited.

  Accordingly, an object of the present invention is to provide an ultrasonic flowmeter that has a small pressure loss and is not easily affected by acoustic noise.

In order to solve the above-mentioned problem, the invention according to claim 1 is an at least one pair of ultrasonic transducers installed at a predetermined distance from the upstream side and the downstream side of the flow path through which the fluid to be measured flows. Propagation time of ultrasonic waves from the ultrasonic transducer on the upstream side to the ultrasonic transducer on the downstream side, and the ultrasonic transducer on the upstream side from the downstream ultrasonic transducer An ultrasonic flowmeter that determines the flow velocity or / and flow rate of the fluid to be measured based on the propagation time of the ultrasonic wave until
A switching unit for switching the transmission / reception direction of the ultrasonic transducer;
A period monitoring unit that outputs a period abnormality signal when a wave outside a predetermined period range is detected;
When the periodic abnormality signal is input, it is determined that the detection of the reception point has failed, and from the peak value of the wave from the time when the periodic abnormality signal is input, the reception point is detected from the beginning. A reception determination unit that outputs a reception signal is provided.
The ultrasonic wave is transmitted plural times in each direction, and the flow velocity and / or flow rate of the fluid to be measured is obtained based on the average value of the propagation time of the ultrasonic wave that has successfully detected the reception point in each direction. Is an ultrasonic flowmeter characterized by

  According to a second aspect of the present invention, in the ultrasonic flowmeter according to the first aspect, the reception determining unit monitors a peak value of the wave from the start of detection of the reception point, and is multiplied by a predetermined value with respect to the wave immediately before that. When there is a wave with the above peak value, the zero-cross point of that wave is detected as a reception point, and if it is determined that detection of the reception point has failed, detection of the reception point from that point should be performed from the beginning. It is characterized by.

According to a third aspect of the present invention, in the ultrasonic flowmeter according to the second aspect, the reception determination unit has a plurality of reference voltage levels determined so that the voltages are arranged in an exponential function, and the reception point detection starts. When a certain wave exceeds a predetermined number from a smaller one of the reference voltage levels not exceeded by the immediately preceding wave, the wave is determined to be more than a predetermined multiple of the immediately preceding wave,
At least when a wave exceeding the predetermined number from the larger one of the plurality of reference voltage levels does not exceed the predetermined number from the smaller one of the reference voltage levels not exceeded by the immediately preceding wave, the reception point It is characterized in that it is determined that the detection has failed.

  According to a fourth aspect of the present invention, in the ultrasonic flowmeter according to any one of the first to third aspects, the reception determination unit has a predetermined number of wave cycles after the detection of the reception point. It is characterized in that the condition within the periodic range is a condition for successful detection of the reception point.

  When a wave outside the predetermined period range is detected, a periodic abnormality signal is output.When the periodic abnormality signal is input, it is determined that the detection of the reception point has failed, and from the time when the periodic abnormality signal is input. By detecting the reception point from the beginning of the wave peak value, it is possible to prevent the acoustic noise from being mistakenly recognized as a signal wave and to accurately measure the flow rate of the fluid to be measured. In addition, an ultrasonic flow meter can be installed in the vicinity of an acoustic noise source such as a valve or a governor.

  Further, since the received signal is electrically processed without providing a strainer or the like, the acoustic noise and the signal wave are discriminated, so that pressure loss can be suppressed as compared with the prior art.

  In order to make the detection of the reception point successful, the invention according to the second aspect includes more acoustic noise in addition to the wave frequency, including whether or not the wave height value is a predetermined value or more with respect to the previous wave. It is possible to prevent erroneous recognition as a signal wave, and to accurately measure the flow rate of the fluid to be measured.

The block diagram of the ultrasonic flowmeter in Example 1 of this invention. An example of a received wave. The figure for demonstrating the reception method in Example 2 of this invention. The block diagram of the reception determination part in Example 3 of this invention.

A mode for carrying out the present invention will be described based on an embodiment shown in the drawings.
[Example 1]
FIG. 1 is a block diagram illustrating the overall configuration of the ultrasonic flowmeter 1 according to the first embodiment. As shown in FIG. 1, the ultrasonic flowmeter 1 includes a flow path (not shown) through which a gas such as a gas to be measured and a liquid such as tap water flow, and a pair of ultrasonic transducers (hereinafter referred to as “a measurement target fluid”). , 2, 3, switching unit 4, control unit 5, transmission unit 6, amplification unit 7, period monitoring unit 8, reception determination unit 9, and arrival time integration unit 10. Have.

  The ultrasonic flow meter 1 has a flow path (not shown) through which a fluid to be measured flows, and a pair of ultrasonic transducers 2 and 3 are spaced apart from each other at a certain distance between the upstream side and the downstream side of the flow path. Are provided relative to each other.

  The two transducers 2 and 3 can be switched to each other so that when one of them is set as the transmission side by the switching unit 4, the other is used as the reception side.

  When a transmission command signal is sent from the control unit 5, the transmission unit 6 sends a drive signal in response to the transmission command signal to the transmitter / receiver 2 (3) via the switching unit 4. In addition, the control unit 5 transmits a transmission command signal to the transmission unit 6 and also transmits the transmission command signal to the arrival time integration unit 10.

  In response to the direction switching signal from the control unit 5, the switching unit 4 sends a transmission command to the transmission unit 6 from the control unit 5 in the case of transmitting / receiving ultrasonic waves in the forward direction (from the upstream side to the downstream side). When the signal is sent, the drive signal from the transmitter 6 is sent to the upstream transducer 2 and the signal from the downstream transducer 3 is sent to the amplifier 7. In the case of transmission / reception of ultrasonic waves in the reverse direction (from the downstream side to the upstream side), when a transmission command signal is sent from the control unit 5 to the transmission unit 6, the drive signal from the transmission unit 6 is sent to the downstream side. The signal is sent to the transducer 3 and the signal from the upstream transducer 2 is sent to the amplifier 7.

  The transmitter / receiver 2 (3) on the transmission side is driven by a drive signal transmitted via the switching unit 4 to generate an ultrasonic wave, and transmits the ultrasonic wave to the transmitter / receiver 3 (2) on the reception side. . The transmitter / receiver 3 (2) on the receiving side receives the transmitted ultrasonic wave, converts it into an electrical signal, and sends it as a received signal to the amplifying unit 7 via the switching unit 4.

  The amplifying unit 7 amplifies the reception signal transmitted from the receiving-side transducer 3 (2) via the switching unit 4 with a predetermined amplification degree. The amplified reception signal is sent to the period monitoring unit 8 and the reception determination unit 9.

  The cycle monitoring unit 8 monitors whether the time between the previous zero cross point and the current zero cross point in the received signal is within a predetermined time range (predetermined cycle range), and the time is within the predetermined time range. If not (out of the time range), a periodic abnormality signal is output to the reception determination unit 9. The predetermined time range is a time range having a predetermined time width centered on the half-wavelength time of the ultrasonic wave transmitted from the transducer 2 (3). This predetermined time range can be adjusted according to the installation state of the ultrasonic flowmeter 1 or the like.

  When the transmission command signal is sent to the transmission unit 6 and detection of the reception point is started, the reception determination unit 9 detects the reception point from the peak value of the amplified reception signal. In this embodiment, a reference voltage level is provided, and a zero cross point of a wave that first exceeds the reference voltage level is set as a reception point. However, when a periodic abnormality signal is input from the periodic monitoring unit 8, it is determined that the detected reception point is incorrect, the reception point is discarded, and detection of the reception point is performed from the time when the periodic abnormality signal is input. It is supposed to restart.

  When the reception determination unit 9 successfully detects the reception point, the reception determination unit 9 sends a reception signal to the arrival time integration unit 10.

  The arrival time integrating unit 10 measures the time from the transmission command signal to the reception point and stores the arrival time. It should be noted that the reception signal is accumulated until the next transmission command signal is sent from the control unit 5 to the transmission unit 6 or within a predetermined time after the transmission command signal is transmitted from the control unit 5. If the input is not input to the unit 10, the reception point cannot be detected in the current transmission of the ultrasonic wave, and the arrival time is not stored because the detection of the reception point fails.

  The control unit 5 sends a direction switching signal to the switching unit 4 to switch the transmission direction of the ultrasonic waves between the transducers 2 (3), and measures the arrival times in the forward direction and the reverse direction, respectively, a predetermined number of times. . In this embodiment, a total of 128 measurements are performed 64 times on each side. In addition, the measurement in the forward direction and the reverse direction may be performed while alternately switching one by one. Alternatively, after the measurement in the forward direction or the reverse direction is performed a predetermined number of times, the measurement is switched alternately and the total number of measurements is a predetermined number. It may be performed until the number of times is reached. After performing the predetermined number of times of measurement, the control unit 5 reads out the arrival times in the forward direction and the reverse direction in which the reception point has been successfully detected from the arrival time integrating unit 10, and calculates the estimated time from the average value of each. The flow velocity and / or flow rate of the measurement fluid is calculated.

  Arbitrary means can be used as a method for calculating the respective average values from the arrival times in the forward direction and the reverse direction. For example, a received signal is input to the arrival time integrating unit 10 or period monitoring is performed. The arrival time when the period abnormality signal is input from the unit 8 to the arrival time integrating unit 10 as a signal indicating the success or failure of the reception of the ultrasonic wave and the reception point is successfully detected in each of the forward and reverse directions. And a function for counting the number of times the reception point has been successfully detected, and after a certain time, the control unit 5 determines the arrival time integration values in the forward and reverse directions from the arrival time integration unit 10. Then, the number of successful reception detections is read and the average value of each is calculated.

Next, a detection method of a reception point will be described based on an example of the reception wave shown in FIG.
FIG. 2 shows a signal wave at a timing when the acoustic noise is small. In the acoustic noise before this signal wave, the reference voltage level is exceeded at points A, B and C, but the time from the previous zero cross point to the zero cross point immediately after each point is within a predetermined time range. Therefore, a periodic abnormality signal is output from the periodic monitoring unit 8. For this reason, it is determined that the detection of the reception point has failed and is discarded, and the detection of the reception point is executed from the beginning again when each periodic abnormality signal is input. On the other hand, since the point D in the signal wave first exceeds the reference voltage level after the last abnormal period signal is output, and the period of the wave is within a predetermined period range, the period monitoring unit 8 Is detected as a reception point without a periodic abnormality signal being output.

  Thus, if the acoustic noise is small at the time of reception, it becomes possible to detect the reception point even if the acoustic noise is large in other time zones. In this embodiment, the number of times of ultrasonic transmission is 64 times. If the reception point is successfully detected, the flow velocity and / or flow rate can be calculated. For example, if a signal wave with little acoustic noise can be detected even once among 64 transmissions, the flow rate and the like can be calculated based on the signal wave.

  Furthermore, it is known that the acoustic noise increases as the flow rate of the fluid to be measured increases, and if there is acoustic noise at a level that hinders the transmission and reception of ultrasonic waves, the flow rate of the fluid to be measured is large. It can be said that. In this case, the arrival time difference between the forward direction and the reverse direction becomes large, and a sufficient resolution can be obtained even with a single measurement result.

  In addition, the flow velocity and / or flow rate of the fluid to be measured is calculated accurately by adopting only the signal wave with small acoustic noise, without detecting the signal wave with large acoustic noise. The flow rate can be measured and / or the ultrasonic flow meter 1 can be installed near a source of acoustic noise such as a governor or a valve or in a place where the acoustic noise is large.

  In addition, since the present application is electrically processed and it is not necessary to install a strainer or the like as in the prior art, pressure loss can be made lower than that in the prior art.

  In the first embodiment, the reception signal amplified by the amplifying unit 7 is input to the period monitoring unit 8 and the reception determining unit 9, and compared with the zero level in each of the period monitoring unit 8 and the reception determining unit 9. The period of the received signal is monitored or the reception point is detected. The amplified received signal is compared with the zero level by either the period monitoring unit 8 or the reception determining unit 9, The result may be supplied to the other.

  The amplification unit 7, the cycle monitoring unit 8, and the reception determination unit 9 take into account the maximum sound speed and the distance between the ultrasonic transducers 2 and 3 after the transmission command signal is transmitted from the control unit 5. The current consumption may be suppressed by operating only after the determined predetermined time until reception point detection or timeout.

  In the above-described embodiment, a pair of ultrasonic transducers 2 and 3 are provided on the upstream side and the downstream side of the flow path, but at least one ultrasonic transducer is provided on the upstream side and the downstream side. There may be a pair, and a plurality of pairs such as two pairs may be provided.

[Example 2]
The second embodiment is different from the first embodiment in the reception determination unit, and is otherwise the same as the first embodiment.

  As shown in FIG. 3, the reception determination unit of the second embodiment has a plurality of reference voltage levels, voltages at the plurality of reference voltage levels are set exponentially, and the number and value of the voltages are signal waves. Set arbitrarily according to the waveform. This reception determination unit, when a certain wave exceeds a predetermined number from a smaller one of the reference voltage levels not exceeded by the immediately preceding wave, the peak value of the wave is compared with the peak value of the immediately preceding wave. Therefore, it can be determined that the peak hold circuit or AD conversion circuit is not used. In addition, if the wave exceeding the predetermined level from the larger one of the plurality of reference voltage levels does not exceed the predetermined number from the smaller one of the reference voltage levels not exceeded by the immediately preceding wave, it is more than that. Even if the detection is continued, since a predetermined number of reference voltage levels are not left, it is determined that the detection of the received wave has failed.

  In the second embodiment, the reference voltage levels are Th1, Th2 (= 1.6 × Th1), Th3 (= 1.6 × Th2 = 2.56 × Th1), Th4 (= 1.6 × Th3 = 4). .10 × Th1), Th5 (= 1.6 × Th4 = 6.55 × Th1), and Th6 (= 1.6 × Th5 = 10.49 × Th1).

  Initially, the system waits at three reference voltage levels, Th1, Th2, and Th3, which are the lowest voltage. When a wave in the received signal exceeds some of the three reference voltage levels, the next three reference voltages are excluded when the next wave is received, excluding the reference voltage level that the previous wave exceeded. At the level, you are ready to wait. When a periodic abnormality signal is input, the standby reference voltage level is changed to Th1, Th2, and Th3, which are the three lowest reference voltage levels that are the first stage.

A reception point detection method will be described with reference to FIG.
When receiving the first wave, it waits at three reference voltage levels of Th1, Th2, and Th3. When the first wave exceeds Th1, it waits at the three reference voltage levels of Th2, Th3, and Th4 when receiving the third wave. Then, the third wave exceeds all three reference voltage levels at once, and the third wave is 1.6 × 1.6 = 2.56 times or more than the first wave which is the immediately preceding wave. It can be seen that it has a size. Thus, when a certain wave exceeds all three levels, it can be seen that it is 2.56 times or more immediately before. The signal wave in the ultrasonic flowmeter 1 of the present embodiment has a waveform as shown in FIG. 3, the third wave is about four times the first wave, and the fifth wave is 1.2 to 3 times the third wave. It has a feature that it is 1.3 times as large, and a certain wave is more than twice the previous wave, that is, a certain wave is from the smaller reference voltage level that the previous wave does not exceed. When three waves are exceeded at once, the wave is likely to be the third wave, and the zero cross point of such a wave is set as the reception point.

  If the wave exceeding the fourth level Th4 does not exceed the third level at a stretch, there are no more than three reference voltage levels that have not been exceeded, and the next wave is more than twice the current wave. Since it is not possible to determine whether or not the reception is failed, the reference voltage levels are switched to the initial three reference voltage levels Th1, Th2, and Th3.

  Also, if the first wave exceeds the lowest reference voltage level Th1, Th2, Th3 by three at a stretch, it will be assumed that reception has failed as an acoustic noise whose period coincides with the signal wave. It has become. When the previous wave exceeds some of the reference voltage levels and a certain wave exceeds three reference voltage levels all at once, it is determined as a signal wave (the third wave), so that more acoustic noise is generated. Can be prevented from being mistakenly determined.

  The third wave is detected as a reception point by the cycle monitoring unit 8 only when the cycle of the wave is within a predetermined time range, as in the first embodiment.

Also in the second embodiment, the same effects as in the first embodiment are obtained.
Furthermore, in the second embodiment, there is a moment when the acoustic noise has the same frequency as the signal wave, and there is a possibility of acoustic noise even if the period of the wave is within a predetermined range. In addition to the period of the wave, By making the detection value of the reception point that the peak value of a certain wave is a predetermined value or more with respect to the immediately preceding wave, it is possible to prevent erroneous determination of acoustic noise as a signal wave.

  If the peak value of a certain wave is more than a predetermined value with respect to the immediately preceding wave using a peak hold circuit, an AD converter circuit, etc., and a periodic abnormality signal is not input, You may make it determine the zero crossing point of a wave as a receiving point.

[Example 3]
The third embodiment is different from the first and second embodiments in the reception determination unit and is otherwise the same as the first and second embodiments.

  The reception determination unit 11 of this embodiment is configured as shown in FIG. The reception signal amplified by the amplification unit 7 is input to the zero comparison unit 12 and the reference voltage level comparison unit 13. The zero comparison unit 12 outputs a zero cross signal when the reception signal becomes zero level.

  Similar to the second embodiment, the reference voltage level comparison unit 13 has a plurality of reference voltage levels, detects the third wave in the same manner as the detection of the reception point in the second embodiment, and detects the third wave. Is detected, a third wave detection signal is output to the reception point detection unit 14. Note that switching of the reference voltage level in the reference voltage level comparison unit is performed at the timing when the zero cross signal from the zero comparison unit 12 is input.

  The reception point detection unit 14 outputs a reception signal to the wave number counting unit 15 and the arrival time integration unit 10 with the timing of zero cross signal input after the third wave detection signal as a reception point.

  The wave number counting unit 15 receives the zero cross signal and counts the wave number after detection after the reception signal is input. In addition, an abnormal period signal is input to the wave number counting unit 15 from the period monitoring unit 8 (not shown), and whether a predetermined number of wave periods are within a predetermined period range even after the reception signal is input. It is determined whether or not. The arrival time integrating unit determines that the reception point has been successfully detected when the predetermined number of wave cycles are within the predetermined period range, and that the reception point has failed to be detected otherwise. When the arrival time integrating unit 10 outputs the wave number determination signal to the reception point 10 and succeeds in detecting the reception point, the arrival time addition or the count of the reception point detection success number is increased. However, the arrival time is not added, and the number of successful detections of reception points is not counted. The width of the predetermined period range may be changed before and after the detection of the reception point. For example, after the detection of the reception point, the width of the predetermined period range is larger than that before the detection of the reception point. Reduce the width.

  When the abnormal period signal is input to the reference voltage level comparison unit 13 (not shown), the reference voltage level is returned to the initial state. When the abnormal period signal is input to the reception point detection unit 14, detection of the reception point is resumed from that point. When the abnormal period signal is input to the wave number counting unit 15, the count value is reset.

DESCRIPTION OF SYMBOLS 1 Ultrasonic flowmeter 2,3 Ultrasonic transducer 5 Control part 8 Period monitoring part 9,11 Reception determination part Th1-6 Reference voltage level

Claims (4)

Ultrasound is transmitted and received by at least one pair of ultrasonic transducers installed at a predetermined distance on the upstream side and downstream side of the flow path through which the fluid to be measured flows, and downstream from the upstream ultrasonic transducer. The flow velocity of the fluid to be measured based on the propagation time of the ultrasonic wave to the ultrasonic transducer on the side and the propagation time of the ultrasonic wave from the ultrasonic transducer on the downstream side to the ultrasonic transducer on the upstream side Or / and an ultrasonic flow meter for determining the flow rate,
A switching unit for switching the transmission / reception direction of the ultrasonic transducer;
A period monitoring unit that outputs a period abnormality signal when a wave outside a predetermined period range is detected;
When the periodic abnormality signal is input, it is determined that the detection of the reception point has failed, and from the peak value of the wave from the time when the periodic abnormality signal is input, the reception point is detected from the beginning. A reception determination unit that outputs a reception signal is provided.
The ultrasonic wave is transmitted plural times in each direction, and the flow velocity and / or flow rate of the fluid to be measured is obtained based on the average value of the propagation time of the ultrasonic wave that has successfully detected the reception point in each direction. Ultrasonic flow meter characterized by.   The reception determination unit monitors the peak value of the wave from the start of detection of the reception point, and when there is a wave whose peak value is equal to or greater than a predetermined value with respect to the immediately preceding wave, the zero cross point of the wave is determined. The ultrasonic flowmeter according to claim 1, wherein when the detection is made as a reception point and it is determined that the detection of the reception point is unsuccessful, the reception point is detected from the beginning. The reception determination unit has a plurality of reference voltage levels determined so that the voltages are arranged exponentially, and a certain wave is smaller of the reference voltage levels not exceeding the wave immediately before the reception point detection start. When the predetermined number is exceeded at once, the wave is determined to be more than a predetermined multiple of the previous wave,
At least when a wave exceeding the predetermined number from the larger one of the plurality of reference voltage levels does not exceed the predetermined number from the smaller one of the reference voltage levels not exceeded by the immediately preceding wave, the reception point The ultrasonic flowmeter according to claim 2, wherein it is determined that the detection of the sensor has failed. The reception determination unit, as a condition for successful detection of a reception point, that a period of a predetermined number of waves is within a predetermined period range even after detection of the reception point. 4. The ultrasonic flowmeter according to any one of items 1 to 3.

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