JP2012058186A - Ultrasonic flowmeter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an ultrasonic flowmeter that reduces a measurement error by setting the frequency of an ultrasonic wave to be output more suitably.SOLUTION: The ultrasonic flowmeter is configured to output an ultrasonic signal into a pipe in which a fluid flows and to calculate the flow rate of the fluid based upon a reflected signal of the ultrasonic signal, and includes: a temperature acquisition part which acquires the temperature of the pipe, and a transmission frequency setting part which calculates the sound velocity in the pipe based upon the acquired temperature of the pipe, and sets the frequency of the ultrasonic signal according to a predetermined rule for reducing a measurement error by using the calculated sound velocity in the pipe.

Description

  The present invention relates to an ultrasonic flowmeter, and more particularly to a technique for appropriately setting the frequency of ultrasonic waves to be output.

  The ultrasonic flowmeter assumes that ultrasonic reflectors such as bubbles and particles contained in the fluid to be measured flowing in the pipe move at the same speed as the fluid to be measured, and obtains these moving speeds to measure Measure fluid flow velocity distribution and flow rate.

  In the ultrasonic flowmeter, the Doppler method is used as one of the methods for obtaining the moving speed of the ultrasonic reflector. As shown in FIG. 5, the Doppler method uses an ultrasonic transducer 220 fixed to a sound-propagating wedge 210 attached to an outer peripheral surface of a pipe 30 through which a fluid to be measured flows, so that an ultrasonic wave having a specific frequency can be obtained. A sound wave signal is obliquely incident on the pipe 30 through the wedge 210, and an echo wave reflected by the ultrasonic reflector 310 in the fluid to be measured is received by the ultrasonic transducer 220.

  The echo wave reflected by the ultrasonic reflector 310 changes in frequency according to the moving speed of the ultrasonic reflector 310 due to the Doppler effect. Therefore, by detecting this change amount, the fluid to be measured flowing in the pipe 30 Can be determined.

  Since reflection by the ultrasonic reflector 310 occurs in various places in the pipe 30, the velocity distribution of the fluid to be measured can be obtained in the radial direction, and the obtained velocity distribution is integrated along the cross-sectional area of the pipe 30. Thus, the flow rate of the fluid to be measured can be calculated.

  Also, with the same configuration, an ultrasonic signal is emitted a plurality of times at time intervals ΔT, a correlation operation is performed on a plurality of echo wave signals from the ultrasonic reflector, and a waveform with a high correlation coefficient is reflected by the same ultrasonic wave By calculating the position and moving speed of the ultrasonic reflector based on the propagation time and the time difference, the flow velocity distribution in the pipe is obtained and the fluid flow rate is calculated. A reflection correlation method is also used.

  In an ultrasonic flowmeter, as shown in an example in FIG. 6, it is known that an error in measured flow rate varies depending on the frequency of ultrasonic waves to be output. In the example of this figure, a difference of several percent occurs in the measurement error depending on the frequency of the output ultrasonic signal. This is because, as shown in FIG. 7, the waves that are reflected multiple times on the wall of the pipe 30 overlap with the ultrasonic signal for measurement.

  Therefore, in Patent Document 1, the measurement error of the ultrasonic flowmeter is reduced by obtaining the frequency at which the multiple waves that affect the reflected signal are reduced from the thickness of the pipe 30 and the speed of sound in the pipe 30. Is described.

JP 2006-30041 A

  Since the speed of sound in the pipe 30 varies depending on the material of the pipe 30, conventionally, a table in which the speed of sound for each material is recorded is prepared, and the speed of sound in the pipe 30 is set according to the material of the pipe 30 set by the user. It was set to calculate an appropriate frequency that would reduce the measurement error.

  However, since the speed of sound in the pipe 30 varies depending on conditions other than the material, the frequency calculated by the conventional method is not necessarily an appropriate value.

  Accordingly, an object of the present invention is to more appropriately set the frequency of ultrasonic waves to be output in an ultrasonic flow meter and reduce measurement errors.

  In order to solve the above-described problems, an ultrasonic flowmeter of the present invention outputs an ultrasonic signal toward a pipe through which a fluid flows, and calculates the flow rate of the fluid based on a reflection signal of the ultrasonic signal. A flowmeter, a temperature acquisition unit for acquiring the temperature of the pipe, and calculating a sound speed in the pipe based on the acquired temperature of the pipe, and using the calculated sound speed in the pipe And a transmission frequency setting unit that sets the frequency of the ultrasonic signal in accordance with a rule for reducing the measurement error.

  Here, the transmission frequency setting unit can calculate the speed of sound in the pipe using data indicating the correspondence between the temperature of the pipe and the speed of sound in the pipe.

  Moreover, the said temperature acquisition part can acquire the temperature of the said piping based on the detection result of the temperature sensor attached to the said piping.

  ADVANTAGE OF THE INVENTION According to this invention, in the ultrasonic flowmeter, the frequency of the ultrasonic wave to output can be set more appropriately. Thereby, the measurement error can be reduced.

It is a block diagram which shows the structure of the ultrasonic flowmeter which concerns on this embodiment. It is a figure for demonstrating an incident angle and a refraction angle. It is a figure which shows the example of a relationship between piping temperature and piping sound speed. It is a flowchart explaining the processing operation of an ultrasonic flowmeter. It is a figure for demonstrating the structure of the measurement part of an ultrasonic flowmeter. It is a figure which shows an example of the relationship between a transmission frequency and a measurement error. It is a figure for demonstrating the multiple wave in piping.

  Embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing the configuration of the ultrasonic flowmeter according to this embodiment. As shown in this figure, the ultrasonic flowmeter 10 for measuring the flow rate of the fluid to be measured flowing in the pipe 30 is fixed to the wedge 210 having a sound propagation property attached to the outer peripheral surface of the pipe 30 and the wedge 210. The ultrasonic transducer 220, a temperature sensor 230 that detects the temperature of the pipe 30, and the control unit 100 are configured.

  For example, the temperature sensor 230 is disposed so as to contact the outer wall of the pipe 30 so that the temperature of the pipe 30 can be detected with high accuracy. However, the temperature of the pipe 30 may be detected in a non-contact manner using infrared rays or the like.

  The control unit 100 can be configured by an information processing device including a CPU, a memory, a dedicated device, and the like, and includes a transmission control unit 110, a reception processing unit 120, a flow rate calculation unit 130, a flow rate calculation unit 140, a measurement result output unit. 150, a parameter setting unit 160, a parameter storage unit 170, a transmission frequency setting unit 180, and a temperature acquisition unit 190.

  The transmission control unit 110 causes the ultrasonic transducer 220 to output an ultrasonic signal having a frequency set by the transmission frequency setting unit 180 at a predetermined timing. The ultrasonic signal output from the ultrasonic transducer 220 enters the pipe 30 obliquely through the wedge 210.

  The reception processing unit 120 performs digital sampling processing, filtering processing, storage processing in a memory, and the like on the echo wave signal received by the ultrasonic transducer 220. The flow velocity calculation unit 130 calculates the flow velocity distribution of the fluid to be measured flowing in the pipe 30 using the echo wave signal. The flow velocity calculation unit 130 may employ any of the Doppler method and the reflection correlation method.

  The flow rate calculation unit 140 calculates the flow rate of the fluid to be measured that flows in the pipe 30 based on the flow velocity distribution. The measurement result output unit 150 displays the measured flow rate, flow velocity distribution, and the like on an internal or external display device or stores them in a storage device.

  Since the transmission control unit 110, the reception processing unit 120, the flow rate calculation unit 130, the flow rate calculation unit 140, and the measurement result output unit 150 described above can have the same contents as those in the past, detailed description thereof is omitted.

  The parameter setting unit 160 receives parameter settings necessary for measurement from the user and stores them in the parameter storage unit 170. The parameters received by the parameter setting unit 160 are the material of the pipe 30, the thickness t of the pipe 30, the outer diameter of the pipe 30, the speed of sound C1 in the wedge 210, the speed of sound in the pipe (fluid), the incident angle θ1, and the like.

  Here, the incident angle θ1 is an angle when the ultrasonic signal enters the pipe 30 from the wedge 210, as shown in FIG. Further, a refraction angle θ2 described later is an angle after refraction in the pipe 30, that is, an angle when entering the pipe from the pipe 30. This figure also shows the thickness t of the pipe 30, the speed of sound C <b> 1 in the wedge 210, and the speed of sound C <b> 2 in the pipe 30.

  Returning to the description of FIG. 1, the transmission frequency setting unit 180 is a functional unit that sets a transmission frequency so as to reduce the measurement error. The pipe sound speed calculation unit 181, the refraction angle calculation unit 182, and the transmission frequency calculation unit 183 I have.

Here, the frequency f at which the flow rate error is reduced can be obtained according to [Equation 1] using the refraction angle θ2, the thickness t of the pipe 30, and the sound velocity C2 in the pipe 30 shown in FIG.

  However, m is assumed to be 1.5, 2.5, 3.5..., Which is a non-resonant frequency, or 1, 2, 3 which is a resonant frequency.

  As shown in [Equation 1], the frequency f at which the flow rate error is small depends on the sound velocity C2 (transverse sound velocity) in the pipe 30. For this reason, in order to reduce the flow rate error, it is necessary to appropriately set the sound velocity C2 in the pipe 30.

  In this embodiment, the pipe sound speed calculation unit 181 calculates the sound speed C2 in the pipe 30 in consideration of the temperature of the pipe 30 in addition to the conventional pipe material and the like. That is, the pipe sound speed C2 varies with the pipe temperature T even if the material is the same, as shown in FIG.

  For this reason, by calculating the frequency f using the pipe sound velocity C2 corresponding to the pipe temperature T, the frequency f of the ultrasonic wave to be output can be set more appropriately, and the measurement error can be reduced. The pipe sound speed calculation unit 181 acquires the temperature of the pipe 30 detected by the temperature sensor 230 via the temperature acquisition unit 190.

  The pipe sound speed calculation unit 181 includes, for example, a temperature sound speed correspondence table 184 prepared for each pipe material. By referring to the temperature sound speed correspondence table 184, the pipe sound speed calculation unit 181 determines the pipe temperature T acquired via the temperature acquisition unit 190. The corresponding pipe sound speed C2 is calculated. Alternatively, a function C2 = f (T) representing the relationship between the pipe temperature T and the pipe sound speed C2 is recorded for each pipe material, and the pipe sound speed C2 corresponding to the acquired pipe temperature T is calculated. Also good.

Returning to the description of FIG. 1, the refraction angle calculation unit 182 uses the pipe sound speed C2 calculated by the pipe sound speed calculation unit 181 to calculate the refraction angle θ2 according to Snell's law expressed by [Equation 2]. At this time, the sound velocity C1 in the wedge 210 may be corrected based on the temperature of the wedge 210.

  The transmission frequency calculation unit 183 calculates the frequency f according to [Equation 1] using the calculated pipe sound speed C2 and the refraction angle θ2, and outputs the frequency f to the transmission control unit 110.

  Next, the processing operation of the ultrasonic flowmeter 10 in the present embodiment will be described with reference to the flowchart of FIG.

  First, the parameter setting unit 160 receives parameter settings necessary for measurement from the user (S101). Here, the parameters to be accepted are the material of the pipe 30, the thickness t of the pipe 30, the outer diameter of the pipe 30, the speed of sound C1 in the wedge 210, the incident angle θ <b> 1, etc., and may be accepted only once before measurement. The accepted parameters are stored in the parameter storage unit 170.

  Next, the pipe temperature T is measured (S102), and the pipe sound speed calculation unit 181 calculates the pipe sound speed C2 based on the measured temperature T (S103). Then, using the calculated pipe sound speed C2, the refraction angle calculation unit 182 calculates the refraction angle θ2 (S104). When the pipe sound speed C2 and the refraction angle θ2 are calculated, the transmission frequency calculation unit 183 calculates the frequency f according to [Equation 1] (S105).

  Then, the transmission control unit 110 emits the ultrasonic signal having the calculated frequency f from the ultrasonic transducer 220 at a predetermined timing (S106). At this time, if the Doppler method is adopted as the measurement method, it is attached at least once, and if the reflection correlation method is adopted, it is attached at least once and more than twice. Sound wave signal emission.

  When the echo wave signal from the ultrasonic reflector moving in the fluid to be measured is received (S107), the flow velocity calculation unit 130 calculates the flow velocity distribution of the fluid to be measured flowing in the pipe 30 using the echo wave signal. (S108).

  Specifically, when the Doppler method is adopted, the flow velocity distribution is obtained by detecting the amount of change of the frequency of the echo wave signal from the frequency f of the output ultrasonic signal. When the reflection correlation method is adopted, correlation calculation is performed on a plurality of echo wave signals from the ultrasonic reflector, and a waveform with a high correlation coefficient is a reflected signal from the same ultrasonic reflector. As a result, the flow velocity distribution in the pipe is obtained by calculating the position and moving speed of the ultrasonic reflector based on the propagation time and the time difference.

  Then, the flow rate calculation unit 140 calculates the flow rate of the fluid to be measured by integrating the obtained velocity distribution along the cross-sectional area of the pipe 30 (S109). The calculation result is output by the measurement result output unit 150 to a display device or the like provided inside or outside the ultrasonic flow meter 10 (S110). However, a plurality of measurement results may be accumulated and output after performing abnormal value elimination processing, averaging processing, and the like.

  By repeating the above-described processing after the pipe temperature measurement (S102) until the flow rate measurement is completed (S111), it is possible to set an appropriate frequency in consideration of the change in the pipe sound speed due to the pipe temperature. The measurement error in the total 10 can be reduced.

  When the pipe temperature T is stable, the pipe temperature measurement (S102), pipe sound speed calculation (S103), refraction angle calculation (S104), and transmission frequency calculation (S104) must be performed each time. For example, it may be performed every predetermined number of times, every predetermined time, or when the environmental temperature changes.

  In the above example, the detection result of the temperature sensor 230 attached to the outer wall of the pipe 30 is used as the pipe temperature T. For example, the pipe temperature T is estimated by measuring the temperature of the fluid to be measured. Alternatively, the pipe temperature T may be estimated by measuring the surface temperature of the wedge 210.

  Alternatively, the pipe temperature T may be obtained indirectly by detecting values depending on the temperature such as the transverse elastic modulus, Young's modulus, Poisson's ratio, etc. of the pipe 30 without directly detecting the temperature. Furthermore, the pipe sound speed C2 may be actually measured, or the pipe sound speed C2 may be estimated from the sound speed in the wedge 210, the sound speed in the fluid to be measured, or the like.

DESCRIPTION OF SYMBOLS 10 ... Ultrasonic flowmeter, 30 ... Piping, 100 ... Control part, 110 ... Transmission control part, 120 ... Reception processing part, 130 ... Flow velocity calculation part, 140 ... Flow rate calculation part, 150 ... Measurement result output part, 160 ... Parameter Setting unit, 170 ... parameter storage unit, 180 ... transmission frequency setting unit, 181 ... pipe sound speed calculation unit, 182 ... refraction angle calculation unit, 183 ... transmission frequency calculation unit, 184 ... temperature sound speed correspondence table, 190 ... temperature acquisition unit, 210 ... Wedge, 220 ... Ultrasonic vibrator, 230 ... Temperature sensor, 310 ... Ultrasonic reflector

Claims (3)

An ultrasonic flowmeter that outputs an ultrasonic signal toward a pipe through which a fluid flows and calculates a flow rate of the fluid based on a reflection signal of the ultrasonic signal,
A temperature acquisition unit for acquiring the temperature of the pipe;
Based on the acquired temperature of the pipe, the speed of sound in the pipe is calculated, and using the calculated speed of sound in the pipe, the frequency of the ultrasonic signal is determined according to a rule for reducing a predetermined measurement error. A transmission frequency setting section to be set;
An ultrasonic flowmeter comprising:   2. The ultrasonic flowmeter according to claim 1, wherein the transmission frequency setting unit calculates the sound velocity in the pipe using data indicating a correspondence relationship between the temperature of the pipe and the sound speed in the pipe. .   The ultrasonic flowmeter according to claim 1, wherein the temperature acquisition unit acquires the temperature of the pipe based on a detection result of a temperature sensor attached to the pipe.