JP2015222188A - Ultrasonic flowmeter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an ultrasonic flowmeter which can easily set propagation time τ of a connection cable according to each site without performing actual measurement of cable length.SOLUTION: An ultrasonic flowmeter 100 comprises a control unit 122 which controls operation of the ultrasonic flowmeter, an ultrasonic transmission unit 126 which transmits an output signal for outputting an ultrasonic wave, an ultrasonic reception unit 128 which amplifies a received signal to perform A/D conversion, and a connection cable 114a which connects the ultrasonic transmission unit or the ultrasonic reception unit and a transducer. The control unit oscillates a pulse signal from the ultrasonic transmission unit, receives a reflection signal obtained by reflecting the pulse signal on an end edge on the transducer side of the connection cable with the ultrasonic reception unit, and calculates the propagation time of the signal in the connection cable by using the oscillation time of the pulse signal and the reception time of the reflection signal.

Description

  The present invention relates to an ultrasonic flowmeter that measures the flow rate of a fluid flowing in a pipeline using ultrasonic waves.

  Conventionally, there has been known an ultrasonic flowmeter that outputs (injects) an ultrasonic wave from the outside of a pipe through which the fluid flows and measures the flow velocity and flow rate of the fluid by utilizing the property that ultrasonic waves propagate through the substance. It has been. As the principle of the ultrasonic flowmeter, there are those using various methods such as a propagation time difference method and a Doppler method (also referred to as a reflection correlation method).

  As said ultrasonic flow meter, the ultrasonic flow meter of patent document 1 can be mentioned, for example. In the ultrasonic flowmeter of Patent Document 1, a pair of transmission / reception ultrasonic transducers (hereinafter referred to as transducers) are arranged on the upstream side and the downstream side of a pipe. In such an ultrasonic flow meter, the time difference between the propagation time of the ultrasonic wave from the upstream side to the downstream side and the propagation time of the ultrasonic wave from the downstream side to the upstream side is obtained by using the propagation time difference method. The flow velocity of the flowing fluid and the flow rate can be calculated. Further, in the ultrasonic flowmeter of Patent Document 1, the reflection correlation method is performed by receiving, with the same transducer, the reflected wave reflected from the ultrasonic reflector included in the fluid flowing in the pipe by the ultrasonic wave incident from one transducer. It is also possible to calculate the flow rate and flow rate of the fluid.

JP 2005-181268 A

The calculation method of the fluid flow velocity will be described below by exemplifying the propagation time difference method. In the propagation time difference method, the ultrasonic wave propagation time tu from upstream to downstream (hereinafter referred to as upstream propagation time tu) and the ultrasonic wave propagation time td from downstream to upstream (hereinafter referred to as downstream propagation time td). ) Is expressed as in the following Equation 1 and Equation 2. In Equations 1 and 2, L is a distance that propagates in the tube (hereinafter referred to as propagation distance L), C is the speed of sound in the fluid, V is the flow velocity in the tube, θ is the flow velocity in the tube, and the propagation direction of the ultrasonic waves. And the angle. τ is a propagation time of a pipe material, a lining material, a connection cable, and the like.
tu = L / (C−V cos θ) + τ Equation 1
td = L / (C + V cos θ) + τ Equation 2

As shown in Equation 3 below, the propagation time difference Δt is calculated by subtracting the downstream propagation time td from the upstream propagation time tu. Then, using the calculated propagation time difference, the flow velocity of the fluid is obtained by Equation 4, and the flow rate is obtained by multiplying the obtained flow velocity by the cross-sectional area of the pipe. It is assumed that the propagation distance L, the sound speed C, and the angle θ are already known.
Δt = tu−td Equation 3
V≈ (C ² / 2L cos θ) · Δt Equation 4

Here, since the speed of sound C in the fluid is affected by temperature, the value is likely to fluctuate due to temperature change. Therefore, in order to eliminate the sonic velocity C, which is a variable parameter, the propagation time t ₀ with respect to the static fluid is obtained by Equation 5, and as shown in Equation 6, the obtained propagation time t ₀ is substituted into Equation 4 to obtain the flow velocity. calculate. Thereby, an error due to the influence of the sound speed C is excluded.
t ₀ = 1/2 (td + tu) = (L / C) + τ Equation 5
V≈ (L / 2 (t ₀ −τ) ² cos θ) Δt Equation 6

  As described with reference to the above formulas 1 to 6, when obtaining the flow velocity V, the propagation time τ of the pipe material, the lining material, the connection cable, and the like is required. Here, the pipe material and the lining material are values that are known before installation. However, although the material of the connection cable for connecting the transducer and the transducer in the ultrasonic flowmeter is known, the length differs at the installation site. For this reason, with regard to the propagation time τ of the connection cable, the length of the connection cable is measured when installing the ultrasonic flowmeter in the field, and the conversion coefficient for each connection cable (in the case of a coaxial cable) according to the measured length , About 5 to 6 nsec / m).

  As described above, when the length of the connection cable is actually measured for each site, the work efficiency is significantly reduced. For this reason, at present, several types of connection cables are prepared in advance, and the connection time suitable for the site is used, and the propagation time τ is set according to the length of the connection cable used. However, with such a method, it is necessary to carry even connection cables that are not used, leading to an increase in the weight of the apparatus.

  Further, although a propagation time τ corresponding to each connection cable is set, the propagation time τ is not a measured value but a representative value, and is not necessarily a value that matches the actual site. In addition, when measuring the length of the connection cable or using a suitable connection cable among several types of connection cables, measurement accuracy or selection errors can affect measurement accuracy. There is sex.

  In view of such problems, the present invention has an object to provide an ultrasonic flowmeter that can easily set the propagation time τ of a connection cable in accordance with the field without actually measuring the cable length. Yes.

  In order to solve the above-described problem, a typical configuration of an ultrasonic flowmeter according to the present invention is an ultrasonic flowmeter that measures the flow rate of a fluid flowing in a pipe line using ultrasonic waves. A control unit that controls the operation of the flow meter, an ultrasonic transmission unit that transmits an output signal for outputting ultrasonic waves, an ultrasonic reception unit that amplifies the received signal and performs A / D conversion, and ultrasonic transmission A connection cable for connecting the transducer or the ultrasonic reception unit and the transducer, and the control unit oscillates a pulse signal from the ultrasonic transmission unit, and the pulse signal superimposes a reflected signal reflected at the end of the connection cable on the transducer side. The propagation time of the signal in the connection cable is calculated using the oscillation time of the pulse signal and the reception time of the reflected signal.

  According to the above configuration, the propagation time of the signal in the connection cable can be calculated from the time until the pulse signal is oscillated from the ultrasonic transmission unit and the reflected signal reflected by the end of the connection cable is received. it can. Therefore, it is possible to easily set the propagation time of the connection cable without actually measuring the cable length. Moreover, since the propagation time is calculated using the connection cable actually used, the propagation time τ of the connection cable can be set in accordance with the site.

  The ultrasonic flow meter is a transmission type ultrasonic flow meter that calculates a flow velocity based on a difference in propagation time by alternately switching between transmission and reception of ultrasonic waves using two transducers. When measuring the propagation time, it is preferable to switch so that both the ultrasonic transmitter and the ultrasonic receiver are connected to one transducer. According to this configuration, the above-described advantages can be obtained when performing flow rate measurement by the propagation time difference method.

  ADVANTAGE OF THE INVENTION According to this invention, the ultrasonic flowmeter which can set easily the propagation time (tau) of the connection cable according to the field can be provided, without measuring cable length.

It is a figure which illustrates the ultrasonic flowmeter concerning this embodiment. It is a figure explaining the measurement of the propagation time (tau) of the connection cable in the ultrasonic flowmeter of this embodiment. It is a figure which illustrates the waveform of the signal received in the ultrasonic wave receiving part. It is a figure explaining other embodiment of an ultrasonic flowmeter.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. The dimensions, materials, and other specific numerical values shown in the embodiments are merely examples for facilitating understanding of the invention, and do not limit the present invention unless otherwise specified. In the present specification and drawings, elements having substantially the same function and configuration are denoted by the same reference numerals, and redundant description is omitted, and elements not directly related to the present invention are not illustrated. To do.

  FIG. 1 is a diagram illustrating an ultrasonic flow meter according to this embodiment. The ultrasonic flowmeter 100 according to the present embodiment measures the flow rate of the fluid flowing through the inside of the pipe line 102 using a pair of upstream transducer 110a and downstream transducer 110b. As shown in FIG. 1, the ultrasonic flowmeter 100 according to the present embodiment includes an upstream transducer 110a, a downstream transducer 110b, and a converter 120.

  The upstream transducer 110 a is attached to the upstream side in the flow direction of the fluid flowing in the pipe 102, and the downstream transducer 110 b is attached to the downstream side in the flow direction of the fluid flowing in the pipe 102. The upstream-side transducer 110a and the downstream-side transducer 110b are respectively connected to the converter 120 (strictly speaking, the ultrasonic transmission unit 126 or the ultrasonic reception unit 128 accommodated in the converter by connecting cables 114a and 114b which are coaxial cables. )It is connected to the.

  The converter 120 includes a control unit 122, a calculation unit 124, an ultrasonic transmission unit 126, an ultrasonic reception unit 128, and a switching unit 130. The control unit 122 manages and controls the operation of the ultrasonic flowmeter 100 using a semiconductor integrated circuit including a central processing unit (CPU). As will be described later, the calculation unit 124 calculates the signal propagation time in the connection cables 114a and 114b using the pulse signal oscillation time and the reflected signal reception time.

  The ultrasonic transmission unit 126 transmits an ultrasonic input signal (transmission voltage), which is a signal for outputting ultrasonic waves, to the transducer on the ultrasonic transmission side of the upstream transducer 110a or the downstream transducer 110b. That is, a pulsar (pulse generator). The ultrasonic reception unit 128 amplifies the signal (reception signal) of the transducer that has received the ultrasonic wave or the reflected wave of the upstream transducer 110a or the downstream transducer 110b, and converts the reception signal as an analog signal into a digital signal. (A / D conversion).

  Based on the control by the control unit 122, the switching unit 130 switches the connection between the ultrasonic transmission unit 126 and the ultrasonic reception unit 128 and the upstream transducer 110a and the downstream transducer 110b. Specifically, the switching unit 130 includes an upstream transmission switch 132a, a downstream transmission switch 132b, an upstream reception switch 134a, and a downstream reception switch 134b.

  In the switching unit 130, the ultrasonic transmission unit 126 and the upstream transmission switch 132a are connected, so that the ultrasonic input signal from the ultrasonic transmission unit 126 is transmitted to the upstream transducer 110a. Thereby, the upstream transducer 110a functions as a transducer on the side that transmits ultrasonic waves (ultrasonic waves are oscillated from the upstream transducer 110a). On the other hand, in the switching unit 130, the ultrasonic transmission unit 126 and the downstream transmission switch 132b are connected to transmit the ultrasonic input signal from the ultrasonic transmission unit 126 to the downstream transducer 110b. Thereby, the downstream transducer 110b functions as a transducer on the side that transmits ultrasonic waves (ultrasonic waves are oscillated from the downstream transducer 110b).

  In the switching unit 130, the ultrasonic reception unit 128 and the upstream reception switch 134 a are connected, so that an ultrasonic wave or reflected wave reception signal received by the upstream transducer 110 a is transmitted to the ultrasonic reception unit 128. (The upstream transducer 110a functions as a receiving transducer). On the other hand, in the switching unit 130, the ultrasonic reception unit 128 and the downstream reception switch 134 b are connected, so that an ultrasonic wave or reflected wave reception signal received by the downstream transducer 110 b is transmitted to the ultrasonic reception unit 128. (The downstream transducer 110b functions as a receiving transducer).

  When measuring the flow rate and flow velocity of the fluid with the ultrasonic flowmeter 100, the control unit 122 first controls switching of the switching unit 130 (switching of the switch), and the ultrasonic transmission unit 126 and the upstream transmission switch 132a, The ultrasonic receiver 128 and the downstream receiving switch 134b are connected. As a result, the upstream transmission switch 132a and the downstream reception switch 134b are turned on, and the upstream transducer 110a functions as a transmission transducer and the downstream transducer 110b functions as a reception transducer.

  And the control part 122 outputs an ultrasonic wave from the upstream transducer 110a by transmitting an ultrasonic input signal to the upstream transducer 110a by the ultrasonic transmitter 126. Thereafter, the control unit 122 amplifies and A / D-converts the ultrasonic reception signal that passes through the fluid in the pipe 102 and is received by the downstream transducer 110b, from the upstream to the downstream. The propagation time tu of the propagated ultrasonic wave is calculated.

  After calculating the propagation time tu of the ultrasonic wave propagated from the upstream to the downstream, the control unit 122 controls the switching unit 130 to switch the switch. Specifically, the control unit 122 connects the ultrasonic transmission unit 126 and the downstream transmission switch 132b, and the ultrasonic reception unit 128 and the upstream reception switch 134a. As a result, the downstream transmission switch 132b and the upstream reception switch 134a are turned on, and the downstream transducer 110b functions as a transmission transducer and the upstream transducer 110a functions as a reception transducer.

  Subsequently, the control unit 122 outputs an ultrasonic wave from the downstream transducer 110b by transmitting an ultrasonic wave input signal to the downstream transducer 110b by the ultrasonic wave transmission unit 126. Then, the control unit 122 amplifies and A / D-converts the ultrasonic reception signal that passes through the fluid in the pipe 102 and is received by the upstream transducer 110a, from the downstream to the upstream. The propagation time td of the propagated ultrasonic wave is calculated.

  After acquiring the data of the propagation time tu and the propagation time td, the control unit 122 calculates the propagation time difference Δt by subtracting the propagation time td from the propagation time tu in the calculation unit 124, and uses the propagation time difference Δt to calculate the fluid time. Calculate flow rate and flow rate. That is, the ultrasonic flowmeter 100 of this embodiment calculates the flow velocity based on the propagation time difference by alternately switching between transmission and reception of ultrasonic waves using two transducers (upstream transducer 110a and downstream transducer 110b). It is a transmission type ultrasonic flowmeter. Then, the control unit 122 calculates the flow velocity based on the propagation time difference by switching the switching unit 130 and alternately transmitting and receiving ultrasonic waves by the upstream transducer 110a and the downstream transducer 110b.

  Here, when obtaining the flow velocity V, the propagation time τ of the pipe material, the lining material, the connection cable, and the like is required. However, since the propagation time τ of the pipe material and the lining material is known in advance, It can be set. However, the propagation time τ of the connection cables 114a and 114b varies depending on the cable length used in the field. Therefore, in the present embodiment, the propagation time τ of the connection cables 114a and 114b can be set without actually measuring the cable length at the site.

  FIG. 2 is a diagram for explaining the measurement of the propagation time τ of the connection cable in the ultrasonic flowmeter 100 of the present embodiment. In FIG. 2, a case where the propagation time τ of the connection cable 114a is measured will be described as an example. When measuring the signal propagation time τ in the connection cable 114a, first, the control unit 122 in the switching unit 130, the ultrasonic transmission unit 126 and the upstream transmission switch 132a, the ultrasonic reception unit 128 and the upstream reception switch 134a. Connect. That is, as shown in FIG. 2A, the control unit 122 transmits both the ultrasonic transmission unit 126 and the ultrasonic reception unit 128 to the upstream transducer 110a to which the connection cable 114a for measuring the propagation time τ is connected. Connect.

  Subsequently, the control unit 122 transmits a measurement start signal to the ultrasonic transmission unit 126, and in response to this, the ultrasonic transmission unit 126 oscillates a pulse signal. Such a pulse signal can be, for example, one pulse (rectangular wave corresponding to about 10 MHz) having a width of about 50 nsec. The oscillated pulse signal passes through the connection cable 114a and reaches the upstream transducer 110a.

  Here, the transducer (upstream transducer 110a) includes the piezoelectric element 112, and is equivalent to a simple capacitance (generally about several nF) in terms of circuit. Such a transducer and the ultrasonic transmitter 126 and the ultrasonic receiver Generally, a coaxial cable (for example, impedance 50Ω) is used as the connection cable 114a for connecting 128. For this reason, the impedance of the connection end of the connection cable 114a to which the upstream transducer 110a is connected, that is, the end of the connection cable 114a on the transducer side is mismatched.

  As described above, since the end of the connection cable 114a on the transducer side is in an impedance mismatching state, the pulse signal oscillated from the ultrasonic transmission unit 126 is reflected at the end of the transducer, and a reflected signal is generated. The control unit 122 receives this reflected signal at the ultrasonic wave reception unit 128. Then, the control unit 122 calculates the signal propagation time in the connection cable 114 a using the pulse signal oscillation time and the reflected signal reception time in the calculation unit 124.

  FIG. 2B schematically illustrates the waveform of the signal received by the ultrasonic receiving unit 128. The pulse signal oscillated from the ultrasonic transmitter 126 is not only directed to the upstream transducer 110a through the connection cable 114a but also received by the ultrasonic receiver 128 as shown in FIG. 2B. The starting point of the pulse signal received by the ultrasonic receiver 128 may be the oscillation time. In addition, when transmitting the measurement start signal to the ultrasonic transmission unit 126, the control unit 122 also transmits the measurement start signal to the ultrasonic reception unit 128, and sets the time when the ultrasonic reception unit 128 has received the measurement start signal. It may be the oscillation time. However, in this case, in calculating the propagation time τ, it is necessary to consider a circuit delay time from when the ultrasonic transmission unit 126 receives the measurement start signal to when the ultrasonic wave is oscillated.

  FIG. 3 is a diagram illustrating a waveform of a signal received by the ultrasonic receiving unit 128. As described above, the reflected signal reflected at the end of the connection cable 114a is received by the ultrasonic receiving unit 128, and amplified and AD converted. At this time, if the sampling frequency of the ultrasonic receiving unit 128 is, for example, 50 MHz, the sampling interval is 20 nsec.

  FIG. 3A illustrates measurement points a to f when sampling is performed at 6 timings (A to F) at intervals of 20 nsec. The timing at which the reflected signal actually arrives by the ultrasonic receiver 128 is defined as a reception point x. If the measurement point b among the measurement points a to f is determined as the rising propagation time, an error from the actual reception point x occurs. That is, when the sampling frequency is 50 MHz, for example, an error of 20 nsec at maximum may occur. When this is converted into a length, for example, if the connection cable 114a is a coaxial cable having a conversion coefficient of 5 nsec / m, an error of about 4 m occurs.

  In order to reduce the error described above, it is preferable to estimate the reception time of the reflected signal. Here, since the load of the connection cable 114a and the piezoelectric element 112 of the upstream transducer 110a are basically capacitive loads, the voltage waveform shape is a general CR waveform as shown by a broken line in FIG. Become. Therefore, if about three points are measured as in the measurement points a to c in FIG. 3A, the reception point x of the actual reflected signal can be estimated by triangular approximation. According to this estimation method, the error can be reduced to half the sampling frequency, that is, about 10 nsec.

  FIGS. 3B and 3C are diagrams for explaining the measurement range of the propagation time τ of the connection cable 114a, and exemplify a signal reception waveform in the case of a general 50Ω coaxial cable. In a 50Ω coaxial cable, the propagation time is approximately 5 nsec / m per meter, and when the cable length is 10 m, for example, the round-trip propagation time of the cable is 100 nsec. In such a case, as shown in FIG. 3B, the ultrasonic receiver 128 receives the pulse signal (50 nsec) oscillated from the ultrasonic transmitter 126 and the received waveform of the reflected signal reflected at the end of the cable ( (Reception timing) does not overlap. Therefore, the reception time of the reflected signal can be estimated, and the propagation time τ can be calculated.

  On the other hand, when the cable length is shortened, the reception timing of the reflected signal is naturally advanced, so that the reception waveforms of the pulse signal and the reflected signal overlap as shown in FIG. Then, the reception time of the reflected signal cannot be estimated, and the propagation time τ cannot be calculated. From these facts, it is understood that the propagation time τ can be calculated practically when the cable length is 10 m or longer with a general 50Ω coaxial cable. Actually, since the connection cable of the ultrasonic flowmeter is hardly 10 m or less, it is considered that the propagation time τ can be calculated in most sites.

  As described above, according to the ultrasonic flowmeter 100 of the present embodiment, the oscillation time of the pulse signal oscillated from the ultrasonic transmission unit 126 and the reception of the reflected signal reflected by the terminal end of the connection cable 114a. By measuring the time, it is possible to easily calculate the signal propagation time in the connection cable 114a without actually measuring the cable length. Accordingly, the calculation of the propagation time can be automated, and the propagation time measurement work in the field becomes unnecessary, so that the work efficiency can be improved. It is also possible to prevent setting mistakes such as when the propagation time τ is set by the cable length.

  Furthermore, since the propagation time is calculated using the connection cable that is actually used, the influence of the cable type and aging deterioration is excluded, that is, the propagation time τ of the connection cable with high accuracy in line with the site is obtained. Is possible. In addition, since it is not necessary to add parts to the apparatus, the cost is not increased. In the above-described embodiment, the case where the propagation time τ in the connection cable 114a is measured is illustrated. However, when the propagation time τ in the connection cable 114b is measured, the switching unit 130 includes the ultrasonic transmission unit 126 and The downstream transmission switch 132b, the ultrasonic reception unit 128, and the downstream reception switch 134b are connected, and the same processing as described above may be performed.

(Other embodiments)
FIG. 4 is a diagram for explaining another embodiment of the ultrasonic flow meter 100, and the same components as those in the ultrasonic flow meter 100 described above are denoted by the same reference numerals and description thereof is omitted. An ultrasonic flow meter 100a shown in FIG. 4 is a transmission / reflection type ultrasonic flow meter, and includes two ultrasonic transmission units and two ultrasonic reception units. In the ultrasonic flowmeter 100a shown in FIG. 4, the first ultrasonic transmitter 126a and the first ultrasonic receiver 128a are on the same signal line, and the second ultrasonic transmitter 126b and the second ultrasonic receiver 128b. Are also on the same signal line. Therefore, according to the ultrasonic flowmeter 100a, it is possible to measure the propagation time τ of the connection cables 114a and 114b without performing the switching process of the switching unit 130.

  As mentioned above, although preferred embodiment of this invention was described referring an accompanying drawing, it cannot be overemphasized that this invention is not limited to the example which concerns. It will be apparent to those skilled in the art that various changes and modifications can be made within the scope of the claims, and these are naturally within the technical scope of the present invention. Understood.

  INDUSTRIAL APPLICABILITY The present invention can be used for an ultrasonic flowmeter that measures the flow rate of a fluid flowing in a pipeline using ultrasonic waves.

DESCRIPTION OF SYMBOLS 100 ... Ultrasonic flowmeter, 100a ... Ultrasonic flowmeter, 102 ... Pipe line, 110a ... Upstream transducer, 110b ... Downstream transducer, 112 ... Piezoelectric element, 114a ... Connection cable, 114b ... Connection cable, 120 ... Converter , 122, a control unit, 124, a calculation unit, 126, an ultrasonic transmission unit, 126 a, a first ultrasonic transmission unit, 126 b, a second ultrasonic transmission unit, 128, an ultrasonic reception unit, 128 a, a first ultrasonic reception. , 128b... Second ultrasonic wave receiver, 130... Switching unit, 132a... Upstream transmission switch, 132b .. downstream transmission switch, 134a... Upstream reception switch, 134b.

Claims (2)

An ultrasonic flowmeter that measures the flow rate of a fluid flowing in a pipeline using ultrasonic waves,
A control unit for controlling the operation of the ultrasonic flowmeter;
An ultrasonic transmitter that transmits an output signal for outputting ultrasonic waves;
An ultrasonic receiving unit that amplifies the received signal and performs A / D conversion;
A connection cable for connecting the ultrasonic transmitter or the ultrasonic receiver and the transducer;
With
The controller is
A pulse signal is oscillated from the ultrasonic transmitter,
The reflected signal reflected by the end of the connection cable on the transducer side of the connection cable is received by the ultrasonic receiver,
An ultrasonic flowmeter, wherein a propagation time of a signal in the connection cable is calculated using an oscillation time of the pulse signal and a reception time of the reflected signal. The ultrasonic flow meter is a transmission type ultrasonic flow meter that calculates a flow velocity based on a propagation time difference by alternately switching between transmission and reception of ultrasonic waves using two transducers,
The ultrasonic wave according to claim 1, wherein when measuring the propagation time of the signal to the transducer, switching is performed so that both the ultrasonic transmission unit and the ultrasonic reception unit are connected to one transducer. Sonic flow meter.

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