JP2015132488A - Ultrasonic flowmeter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an ultrasonic flowmeter capable of detecting abnormality such as a measurement error, etc., with high accuracy, even when there is a change in a measurement fluid or temperature.SOLUTION: An ultrasonic flowmeter comprises: a characteristic value calculation unit 6 for calculating a value A by A=1/t1+1/t2 from a propagation time t1 of an ultrasonic wave from a first ultrasound transducer 1a to a second ultrasound transducer 1b and a propagation time t2 from the second ultrasound transducer 1b to the first ultrasound transducer 1a, and making the calculated value a characteristic value; a memory unit 9 having a signal intensity detection unit 7 for detecting the intensity of an ultrasonic wave signal and/or a temperature detection unit 8 for detecting a fluid temperature, and preserving the signal intensity detected by the signal intensity detection unit 7 and/or the fluid temperature detected by the temperature detection unit 8 and the characteristic value calculated by the characteristic value calculation unit 6; a determination condition generation unit 10 for generating an abnormality determination condition from the data stored in the memory unit 9; and an abnormality determination unit 11 for determining abnormality from the abnormality determination condition and the characteristic value stored in the memory unit 9.

Description

  The present invention relates to an ultrasonic flowmeter that measures the flow rate of a fluid such as a gas using ultrasonic waves, and more particularly to an ultrasonic flowmeter having an abnormality determination function of a measurement function.

  2. Description of the Related Art In recent years, ultrasonic flow meters that measure the time during which ultrasonic waves travel through a propagation path and measure the flow rate of fluid by measuring the moving speed of the fluid are being used in gas meters and the like.

  FIG. 8 shows a cross-sectional configuration of the main part of this type of ultrasonic flowmeter.

  In the ultrasonic flow meter shown in FIG. 8, the fluid to be measured whose flow rate is to be measured is arranged to flow in the pipe. On the tube wall 102, a pair of ultrasonic transducers 101a and 101b are installed facing each other. The ultrasonic transducers 101a and 101b are configured using a piezoelectric material such as a piezoelectric ceramic as an electromechanical transducer, and exhibit resonance characteristics like a piezoelectric buzzer and a piezoelectric oscillator.

  In the example of FIG. 8, first, the ultrasonic transducer 101a is used as an ultrasonic transmitter, and the ultrasonic transducer 101b is used as an ultrasonic receiver. In this stage, an alternating voltage having a frequency near the resonance frequency of the ultrasonic transducer 101a is applied to the piezoelectric body in the ultrasonic transducer 101a. Then, the ultrasonic transducer 101a functions as an ultrasonic transmitter and radiates ultrasonic waves into the fluid. The emitted ultrasonic wave propagates to the path L1 and reaches the ultrasonic wave transmitter / receiver 101b functioning as an ultrasonic wave receiver. At this time, the ultrasonic transducer 101b functions as an ultrasonic receiver, and receives the ultrasonic waves and converts them into a voltage.

  Next, the ultrasonic transducer 101b functions as an ultrasonic transducer, and the ultrasonic transducer 101a functions as an ultrasonic receiver. That is, by applying an AC voltage having a frequency near the resonance frequency of the ultrasonic transducer 101b to the piezoelectric body in the ultrasonic transducer 101b, ultrasonic waves are radiated from the ultrasonic transducer 101b into the fluid. . The emitted ultrasonic wave propagates along the path L2 and reaches the ultrasonic transducer 101a. The ultrasonic transducer 101a receives the transmitted ultrasonic wave and converts it into a voltage.

  As described above, the ultrasonic transducers 101a and 101b are generally collectively referred to as “ultrasonic transducers” in order to alternately perform a function as a transmitter and a function as a receiver.

  In the ultrasonic flow meter shown in FIG. 8, when an alternating voltage is continuously applied, since ultrasonic waves are continuously emitted from the ultrasonic transducer and it becomes difficult to measure the propagation time, it is usually fixed time. The burst voltage signal is used as the drive voltage so that only ultrasonic waves are transmitted.

  Hereinafter, the measurement principle of the ultrasonic flowmeter will be described in more detail. First, an ultrasonic burst signal is radiated from the ultrasonic transducer 101a by applying a driving burst voltage signal to the ultrasonic transducer 101a. As a result, the ultrasonic burst signal propagates through the path L1 and reaches the ultrasonic transducer 101b after t1 time. The distance of the path L1 is equal to the distance of the path L2, and is L. The ultrasonic transducer 101b can convert only the transmitted ultrasonic burst signal into an electric burst signal with a high S / N ratio.

In FIG. 8, the flow velocity of the fluid flowing in the pipe is V, the velocity of the ultrasonic wave in the fluid is C, and the angle between the direction of flow of the fluid and the propagation direction of the ultrasonic pulse is θ. When the ultrasonic transducer 101a is used as an ultrasonic transmitter and the ultrasonic transducer 101b is used as an ultrasonic receiver, an ultrasonic pulse from the ultrasonic transducer 101a is transmitted to the ultrasonic transducer 101b. If the arrival time is t1, the relationship of (Formula 1) is established.

  t1 = L / (C + Vcos θ) Equation 1

  When the ultrasonic transmitter / receiver 101b is used as an ultrasonic transmitter, the time for the ultrasonic pulse from the ultrasonic transmitter / receiver 101b to reach the ultrasonic transmitter / receiver 101a serving as an ultrasonic receiver is denoted by t2. Then, the relationship of (Formula 2) is established.

  t2 = L / (C−Vcos θ) Equation 2

  Here, the difference between the reciprocals of the propagation times t1 and t2 is expressed by (Formula 3).

  1 / t1-1 / t2 = 2V cos θ / L (3)

  Further, when (Equation 3) is modified, (Equation 4) is obtained.

  V = L / 2 cos θ (1 / t1-1 / t2) Equation 4

  According to (Formula 4), the average flow velocity V of the fluid can be obtained from the distance L of the propagation path of the ultrasonic waves and the propagation times t1 and t2. Then, the flow rate Q can be calculated from the flow velocity V and the cross-sectional area S of the flow path by (Formula 5).

  Q = SV Expression 5

  Thus, since the flow rate is calculated from the propagation time of the ultrasonic wave and the cross-sectional area of the flow path, abnormalities such as measurement errors may occur due to secular changes in the ultrasonic transducers 101a and 101b and the flow path. When an ultrasonic flowmeter with measurement errors is applied to a gas meter, etc., correct measurement values cannot be obtained, and the user does not have specialized knowledge. It was.

  In order to solve such a problem, a method is disclosed in which an abnormality diagnosis is performed by comparing the ultrasonic velocity in the fluid calculated from the propagation time of the ultrasonic wave and the sound velocity calculated from the temperature (Patent Document). 1).

JP-A-8-304135

  In the method of Patent Document 1, a temperature sensor is essential, and the cost is high. In addition, when measuring fluids having different characteristics, there is a problem that it is difficult to cope with a slight measurement error.

  The present invention aims to solve the above-described problems of the prior art, and provides an ultrasonic flowmeter that can cope with the measurement of fluids having different characteristics and can detect abnormalities such as slight measurement errors. There is.

The ultrasonic flowmeter of the present invention includes a flow path through which a fluid flows, a first ultrasonic transducer and a second ultrasonic transducer disposed in the flow path, and the first and second ultrasonic transducers. A transmission / reception unit for transmitting / receiving an ultrasonic signal from the ultrasonic transducer, a propagation time measuring unit for measuring a propagation time of the ultrasonic signal between the first and second ultrasonic transducers, and the ultrasonic signal An ultrasonic flowmeter having a flow rate calculation unit for calculating a flow rate of a fluid from a propagation time,
Propagation time t1 of ultrasonic waves from the first ultrasonic transducer to the second ultrasonic transducer, and from the second ultrasonic transducer to the first ultrasonic transducer From the propagation time t2 of the ultrasonic wave,
A = 1 / t1 + 1 / t2
A characteristic value calculation unit having the value A calculated by the characteristic value, a signal intensity detection unit for detecting the intensity of the ultrasonic signal, and / or a temperature detection unit for detecting the fluid temperature. An abnormality determination condition is generated from the signal intensity to be detected and / or the fluid temperature detected by the temperature detection unit, the memory unit for storing the characteristic value calculated by the characteristic value calculation unit, and the data stored in the memory unit A determination condition generation unit for performing an abnormality determination based on the abnormality determination condition and the characteristic value stored in the memory unit.

  In the present invention, it is preferable to have a characteristic value correction unit that generates a correction characteristic value from the characteristic value using the intensity and / or temperature of the ultrasonic signal, and to perform abnormality determination based on the correction characteristic value.

  In the present invention, it is preferable to have a standard time detection unit that detects standard time, and to perform abnormality determination based on an output value of the standard time detection unit.

  In the present invention, it is preferable to include a display device that displays abnormality determination information and / or a communication device that communicates abnormality determination information.

  The ultrasonic flowmeter of the present invention can detect changes in fluids, slight measurement errors, etc., can respond to abnormalities at an early stage, and can detect abnormalities even for users who do not have specialized knowledge. A sonic flow meter can be provided.

Configuration diagram of ultrasonic flowmeter in Embodiment 1 of the present invention The figure which shows the measurement data stored in the memory part in Embodiment 1 of this invention The figure which shows the determination conditions stored in the memory part in Embodiment 1 of this invention Configuration diagram of ultrasonic flowmeter in embodiment 2 of the present invention The figure which shows the measurement data stored in the memory part in Embodiment 2 of this invention The figure which shows the determination conditions stored in the memory part in Embodiment 2 of this invention The block diagram of the ultrasonic flowmeter in Embodiment 3 of this invention Configuration diagram of conventional ultrasonic flowmeter

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. The present invention relates to an ultrasonic flowmeter capable of determining an abnormality such as a measurement error that occurs over time when it is difficult to preset an abnormality determination condition, such as when the characteristics of a measurement fluid change or the measurement environment changes. Is intended to provide.

(Embodiment 1)
FIG. 1 is a configuration diagram of the ultrasonic flowmeter according to the first embodiment. In FIG. 1, 1a and 1b are ultrasonic transducers, 2 is a flow path, 3 is a transmission / reception unit, 4 is a propagation time measurement unit, 5 is a flow rate calculation unit, 6 is a characteristic value calculation unit, and 7 is a signal intensity detection unit. , 8 is a temperature detection unit, 9 is a memory unit, 10 is a determination condition generation unit, and 11 is an abnormality determination unit.

  The ultrasonic transducers 1a and 1b are provided in the middle of the flow path 2 so as to be opposed to the fluid flow V at a distance L with an angle θ. The ultrasonic wave is transmitted from the ultrasonic transducer, the ultrasonic wave is received by the other ultrasonic transducer, and the received ultrasonic signal is transmitted to the transmission / reception unit 3. In the propagation time measurement unit 4 that has received the ultrasonic signal from the transmission / reception unit 3, the propagation time t1 from one ultrasonic transducer 1a to the other ultrasonic transducer 1b and the other ultrasonic transducer 1b. To propagation time t2 to one ultrasonic transducer 1a. The flow rate calculation unit 5 calculates the flow rate using (Equation 1) to (Equation 5).

  The characteristic value calculation unit 6 uses the value A calculated from the propagation times t1 and t2 from the propagation time measurement unit 4 based on (Equation 6) as the characteristic value.

  A = 1 / t1 + 1 / t2 Expression 6

  The signal strength detection unit 7 detects the signal strength of the ultrasonic signal from the transmission / reception unit 3 and transfers it to the memory unit 9.

  The temperature detection unit 8 detects fluid temperature information from a temperature sensor (not shown) and transfers it to the memory unit 9. In the memory unit 9, information sets of (characteristic value, signal intensity, fluid temperature) from the characteristic value calculation unit 6, the signal intensity detection unit 7, and the temperature detection unit 8 are stored in association with each other as shown in FIG. .

  The determination condition generation unit 10 generates an abnormality determination condition for determining an abnormality based on each piece of information stored in the memory unit 9 and transmits it to the memory unit 9. In the memory unit 9, the abnormality determination condition is stored in a place different from the information set of (characteristic value, signal intensity, fluid temperature).

  The abnormality determination unit 11 compares the abnormality determination condition stored in the memory unit 9 with the information set of (characteristic value, signal strength, fluid temperature), and determines a normal state and an abnormal state. When it is determined as an abnormal state, the abnormality determination information is displayed on a display device (not shown), and the abnormality determination information is communicated from a communication device (not shown) to a gas company or the like. In the present embodiment, the abnormality determination information is configured to be notified by a display device (not shown) and a communication device (not shown). However, only one of the display device and the communication device may be provided. .

  Here, the operation of the determination condition generation unit 10 will be described in detail. The abnormality determination condition is determined as follows, for example. Since the ultrasonic flowmeter is shipped in a state where the measurement performance is ensured in a factory or the like, there is no abnormality such as a measurement error in the initial stage. The characteristic value of the ultrasonic flowmeter in the initial state is set as the reference value in the normal state, and when there is a difference between the reference value and the newly acquired characteristic value, it is determined as abnormal. As an example, the reference value is set to the median value, and, as shown in FIG. 3, conditions such as a normal range from −5% to + 5% of the reference value can be set to determine that an abnormality occurs when the reference value is outside the normal range. .

  At this time, the abnormality determination conditions are stored together with the ultrasonic signal intensity and the fluid temperature, and the abnormality determination is performed by comparing characteristic values having the same signal intensity and fluid temperature in the abnormality determination. . This is due to the following reason.

  When (Formula 6) for calculating the characteristic value is rewritten using (Formula 1) and (Formula 2), it can be described as (Formula 7).

  A = 2C / L Expression 7

  As shown in (Formula 7), the characteristic value is described by the sound velocity C of the fluid and the distance L between the ultrasonic transducers 1a and 1b. That is, when the sound speed of the fluid changes, the characteristic value changes. Therefore, it is necessary to compare the characteristic values at the same sound speed.

  The sound speed of the fluid varies depending on the type of fluid and the fluid temperature. For this reason, it is necessary to compare the characteristic value when the fluid type and the fluid temperature are the same.

  As described above, the abnormality determination condition is set from the characteristic value in the initial state, and the fluid to be measured is unknown by comparing the characteristic value obtained under the same condition with the fluid type and the fluid temperature. Even when the measurement environment fluctuates, it is possible to perform measurement abnormality determination with high accuracy.

  When the characteristic values under the same conditions fluctuate, fluctuations in propagation times t1 and t2 due to mixing of mist, dust, etc. that are not normally present in the fluid, changes in electrical characteristics of the ultrasonic transducers 1a and 1b, flow paths It is assumed that an abnormality such as a variation in the distance L due to a deformation or an abnormality in the attachment portion of the ultrasonic transducers 1a and 1b has occurred. When such an abnormality occurs, an event occurs in which the flow rate cannot be measured or a measurement error occurs.

  In this embodiment, the method of comparing characteristic values in which both the temperature and the signal intensity match is described. However, depending on the use environment, it is possible to use the method in which only one of the temperature and the signal intensity is compared. is there.

(Embodiment 2)
FIG. 4 is a configuration diagram of the ultrasonic flowmeter according to the second embodiment. The ultrasonic flowmeter according to the second embodiment is configured in the same manner as the ultrasonic flowmeter according to the first embodiment except that the characteristic value correction unit 13 is provided.

  In the ultrasonic flowmeter of the second embodiment, by correcting the abnormality determination condition by the characteristic value correction unit 13, the variation in the environmental temperature and the type of fluid is large, and it is difficult to obtain the characteristic value under the same condition. It can cope with a case where the determination is difficult. Specifically, abnormality determination is performed by using the corrected characteristic value obtained by correcting the acquired characteristic value with the signal intensity and the fluid temperature and comparing with the characteristic value obtained with different temperatures and different types of fluids.

  In the ultrasonic flowmeter according to the second embodiment, it is possible to make an abnormality determination regardless of the fluid temperature and the signal strength. Therefore, the type of fluid and the fluid temperature are large and stable even in an environment that fluctuates frequently. Can be judged.

  Next, a specific characteristic value correction method will be described. Since the characteristic value fluctuates when the fluid sound velocity C varies as shown in (Formula 7), the fluid sound velocity is virtually corrected to the sound velocity value under the same conditions from the ultrasonic signal intensity and fluid temperature. .

  The correction based on the fluid type uses the signal strength of ultrasonic waves. When the fluid is a gas, there is a correlation between the intensity of the ultrasonic signal and the average molecular weight of the gas, and there is a correlation between the average molecular weight and the speed of sound. That is, there is a correlation between the ultrasonic signal intensity and the sound speed, and the sound speed can be corrected using the ultrasonic signal intensity. Specifically, when the ultrasonic signal intensity is higher than the standard condition, the sound speed is higher than the virtual standard condition. Therefore, the correction is performed so that the sound speed is lower, and a correction characteristic value is derived. When the ultrasonic signal intensity is lower than the virtual standard condition, the sound speed is lower than the standard condition. Therefore, correction is performed so that the sound speed is higher, and a correction characteristic value is derived.

In the correction based on the fluid temperature, when the fluid is a gas, the sound speed increases as the fluid temperature increases, and the sound speed decreases as the fluid temperature decreases. Using this characteristic, a correction characteristic value under standard conditions is derived. The correction characteristic value derived in this way is stored in the memory unit 9 together with the fluid temperature, signal intensity, and characteristic value as shown in FIG.

  Further, the determination condition shown in FIG. 6 is set using the initial value of the correction characteristic value as in the first embodiment. In the second embodiment, since the correction characteristic value is used, it is possible to determine abnormality using all data regardless of fluid temperature and signal intensity information. Therefore, only one determination condition needs to be set. Even when the measurement environment continues to fluctuate, an abnormality can be detected at an appropriate timing.

(Embodiment 3)
FIG. 7 is a diagram illustrating the configuration of the ultrasonic flowmeter according to the third embodiment. The ultrasonic flowmeter in the third embodiment is configured in the same manner as the ultrasonic flowmeter in the first embodiment except that the standard time detection unit 14 is provided and the temperature detection unit and the signal intensity detection unit are removed.

  The fluctuation of the fluid temperature has a large periodicity in the fuel gas meter or the like, and therefore, the fluctuation of the sound velocity C of the fluid also tends to fluctuate periodically every year. Therefore, it is possible to perform abnormality determination by comparing characteristic values in the same month and day in different years, or by comparing variation patterns of characteristic values in one year in different years.

  The standard time detection unit 14 according to the third embodiment includes a memory unit as a value A and a characteristic value calculated by the characteristic value calculation unit 6 together with date information at a predetermined time every day for the first year when the ultrasonic flowmeter is installed. 9 and after one year, the characteristic value calculated at a predetermined time is compared with the characteristic value stored in the memory unit 9 on the same month and the normal range is from -5% to + 5%. It is possible to set a condition for determining that an abnormality occurs when the condition is off.

  Since the ultrasonic flowmeter is shipped in a state where the measurement performance is ensured in a factory or the like, there is no abnormality such as a measurement error in the initial stage. The characteristic value based on the value A calculated in the first year when the ultrasonic flowmeter was installed is set as the reference value for the normal state of the ultrasonic flowmeter in the initial state, and the reference value and the newly acquired characteristic value When a difference occurs, it is determined as abnormal.

  In addition, it is preferable that the abnormality determination is configured to notify the abnormality when the abnormality determination continues for a certain period, for example, one week in consideration of errors such as climate change for each year.

  In the abnormality determination method according to the third embodiment, although there are error factors such as climate change that vary from year to year, the signal intensity detection unit and the temperature detection unit are not required, so that abnormality determination can be realized simply and at low cost. I can do it.

  As described above, in any of the first to third embodiments, the abnormality determination detected by the abnormality determination unit is displayed on a display unit such as a liquid crystal mounted on the flow meter to notify the user in an easy-to-understand manner, or It is possible to provide an ultrasonic flow rate system capable of notifying a flowmeter administrator or the like by a communication device or the like, recognizing an abnormality at an early stage, and responding to the abnormality.

  The ultrasonic flowmeter and the ultrasonic flowmeter system of the present invention have an abnormality detection function capable of detecting an abnormality such as a measurement error occurring during use with high accuracy, and are used for a long period of time. Or it can utilize especially effectively for the ultrasonic flowmeter used in the environment where a user does not have technical knowledge.

DESCRIPTION OF SYMBOLS 1a, 1b Ultrasonic transducer 2 Flow path 3 Transmission / reception part 4 Propagation time measurement part 5 Flow rate calculation part 6 Characteristic value calculation part 7 Signal intensity detection part 8 Temperature detection part 9 Memory part 10 Judgment condition production | generation part 11 Abnormality determination part 13 Characteristic value correction unit 14 Standard time detection unit 101a, 101b Ultrasonic transducer 102 Tube wall

Claims (4)

A flow path through which fluid flows, a first ultrasonic transducer and a second ultrasonic transducer disposed in the flow path, and ultrasonic signals from the first and second ultrasonic transducers The flow rate of fluid is calculated from the transmission time of the ultrasonic signal, the propagation time measurement unit that measures the propagation time of the ultrasonic signal between the first and second ultrasonic transducers, and the propagation time of the ultrasonic signal An ultrasonic flowmeter having a flow rate calculation unit,
Propagation time t1 of ultrasonic waves from the first ultrasonic transducer to the second ultrasonic transducer, and from the second ultrasonic transducer to the first ultrasonic transducer From the propagation time t2 of the ultrasonic wave,
A = 1 / t1 + 1 / t2
A characteristic value calculation unit having the value A calculated by the characteristic value;
A signal intensity detection unit that detects the intensity of the ultrasonic signal and / or a temperature detection unit that detects the fluid temperature;
A memory unit for storing a signal intensity detected by the signal intensity detection unit and / or a fluid temperature detected by the temperature detection unit, and a characteristic value calculated by the characteristic value calculation unit;
A determination condition generation unit that generates an abnormality determination condition from the data stored in the memory unit;
An abnormality determination unit that performs abnormality determination from the abnormality determination condition and the characteristic value stored in the memory unit;
An ultrasonic flow meter comprising. The ultrasonic flowmeter according to claim 1, further comprising: a characteristic value correction unit that generates a correction characteristic value from the characteristic value using the intensity and / or temperature of the ultrasonic signal, and performing abnormality determination based on the correction characteristic value. The ultrasonic flowmeter according to claim 1, further comprising a standard time detection unit that detects standard time, and selecting a characteristic value for performing abnormality determination based on an output value of the standard time detection unit. The ultrasonic flowmeter according to claim 1, further comprising a display device that displays abnormality determination information and / or a communication device that communicates abnormality determination information.

Images