JPH0259404B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an ultrasonic flowmeter that measures the flow velocity of a fluid and has an output correction function for temperature changes in a fluid to be measured. An ultrasonic flow meter transmits and receives ultrasonic waves in the forward and reverse directions with respect to the flow direction of the fluid, and attempts to determine the fluid flow velocity from the difference in propagation time of each ultrasonic wave. FIG. 1 shows a block diagram for explaining the functions of a conventional ultrasonic flowmeter.
In the figure, 1a, 1b, 2a, and 2b are ultrasonic transceivers, 3a, 3b, 4a, and 4b are ultrasonic transceiver mounting members, and 5 is piping.
The ultrasonic transceivers 1a, 1b, 2a, 2b are connected to the piping 5 via ultrasonic mounting members 3a, 3b, 4a, 4b.
It is fixedly installed. Ultrasonic flowmeters detect when ultrasonic waves propagate through a fluid.
This method utilizes the fact that a propagation time difference occurs between the ultrasonic propagation time in the forward direction of the flow direction and the ultrasonic propagation time in the reverse direction with respect to the flow direction, and that the propagation time difference is proportional to the fluid flow velocity. . This will be explained using FIG. 1. As shown in FIG.
4b Let us assume that the ultrasonic propagation time per body is τ ₀ /2, the ultrasonic incident angle θ at the boundary between the pipe wall and the fluid, and the sound speed of the ultrasonic wave in the fluid as Co. Since the sound velocity in the fluid of the ultrasound transmitted in the forward direction of the fluid is sufficiently large compared to the fluid flow velocity, the incident angle does not change and only the sound velocity component of the ultrasound changes.
It becomes Co+Vcosθ. Further, since the propagation distance of the ultrasonic wave is d/sin θ, the propagation time of the ultrasonic wave propagating in the fluid is d/(Co+Vcos θ) sin θ. Therefore, the propagation time t L for the forward-propagating ultrasound to reach the ultrasound transmitter/receiver 2b from the ultrasound transmitter/receiver 1a in FIG. ₁ is t _L = d/(Co+Vcosθ) sinθ+τ ₀ ...(1) Become. Similarly, ultrasonic waves propagating in the opposite direction to the flow direction are transmitted from the ultrasonic transceiver 1b to the ultrasonic transceiver 2a.
The propagation time t _u to reach is t _u =d/(Co−Vcosθ)sinθ+τ ₀ (2). (1). Obtaining the fluid flow velocity V from equation (2), V=d(t _u −t _L )/sin2θ(t _L −τ ₀ )(t _u −τ ₀ )...
…(3) becomes. Here, t _u −t _L is the propagation time difference and △t
Also, since t _L −τ ₀ ≫△t, equation (3) is obtained as V=d/sin2θ(t _u −τ ₀ ) ² △ ...(4). By measuring the propagation time difference Δt in this manner, the fluid flow velocity V can be determined. Conventional ultrasonic flowmeters are based on the operating principle described above, so by measuring the ultrasonic propagation time t _u and the propagation time difference Δt, it can be determined that the ultrasonic sound velocity Co is not included in equation (3). Therefore, temperature correction of the ultrasonic flowmeter output due to fluid temperature changes is possible to a certain extent. However, the pipe inner diameter d,
The ultrasonic incident angle θ and the temperature dependence of τ ₀ due to the use of the ultrasonic transceiver mounting member are not corrected. This point remains a major problem in realizing high-precision ultrasonic flowmeters, and causes difficulties in applying ultrasonic flowmeters to plants, etc. where the fluid to be measured has a wide temperature change range. Ta. This invention was made to eliminate the drawbacks of conventional ultrasonic flowmeters as described above, and does not require a temperature signal of the fluid to be measured, allowing the ultrasonic flowmeter alone to respond to temperature changes in the fluid to be measured. Our goal is to provide a highly accurate ultrasonic flowmeter that enables temperature correction of the output output, and that is highly accurate even when the temperature of the fluid to be measured changes over a wide range due to operating conditions such as nuclear power plants and various other plants. There is. In order to achieve the above object, one embodiment of the present invention will be described below with reference to the drawings. In Figure 2,
1a, 1b, 2a, 2b are ultrasonic transmitter/receivers, 3
a, 3b, 4a, and 4b are ultrasonic transmitter/receiver mounting members corresponding to the ultrasonic transmitter/receivers 1a, 1b, 2a, and 2b, respectively; 5 is a pipe; and 6 is an ultrasonic signal attachment member for the ultrasonic transmitter/receiver elements 1a to 2b. An ultrasonic flowmeter circuit unit for controlling transmission and reception, and measuring the difference in ultrasound propagation time between the forward and reverse directions with respect to the flow direction of the fluid to be measured, and the ultrasound propagation time from ultrasound transmission to reception. , 7 is an ultrasonic flowmeter circuit section 6
This is an output temperature correction calculation unit for the ultrasonic flowmeter output using ultrasonic propagation time and propagation time difference information. FIG. 3 is a detailed configuration diagram showing the function of the output temperature correction calculating section 7 in FIG. 2, in which 8 is an ultrasonic propagation time difference signal, 9 is an ultrasonic propagation time signal,
71 is an amplification regulator for amplifying and adjusting the signal voltage of the ultrasonic propagation time difference signal 8; 72 is a bias circuit section for applying a bias voltage to the signal voltage of the ultrasonic propagation time signal 9; and 73 is an amplifier for the bias circuit section 72. A squarer 74 is a divider for dividing the output voltage of the amplification regulator 71 by the output voltage of the squarer 73. Here, the basic principle of the present invention will be described, and the role of the output temperature correction calculation section 7 in the configuration of an embodiment of the present invention shown in FIG. 2 will be explained. As previously explained, in an ultrasonic flowmeter, the fluid flow velocity can be determined by equation (4) by eliminating the ultrasonic sound velocity in the fluid being measured by measuring the ultrasonic propagation time and the propagation time difference. Also,
Similarly, the relationship between the fluid flow velocity including the contribution of the ultrasonic sound velocity in the fluid to be measured and the ultrasonic propagation time difference in the forward and reverse directions with respect to the flow direction is given by the following equation. V=tanθ・Co ² /2d△t...(5) In other words, equation (5) indicates that the difference in ultrasonic propagation time between the forward and reverse flow directions of the fluid to be measured is proportional to the fluid flow velocity. This is the measurement principle equation of an ultrasonic flowmeter.On the other hand, the ultrasonic sound velocity in the fluid to be measured is eliminated from equation (4) or (5), and the ultrasonic propagation time is measured. This is an actual measurement formula that attempts to determine the fluid flow velocity in response to temperature changes. However, as described above, even if the measurement is performed using equation (4), the output temperature correction for the temperature change of the fluid to be measured in the output of the ultrasonic flowmeter is not sufficient. In the present invention, equations (4) and (5) are placed equal to the fluid flow velocity V, and tanθ・Co ² /2d△t=d/sin2θ・(t _u −τ ₀ ) ² △t, Furthermore, the ultrasonic propagation time difference Δt is eliminated, a component that depends on the temperature change of the fluid to be measured in the ultrasonic flowmeter is extracted, and the above equation is rearranged to obtain the following equation. In equation (6), the ultrasonic propagation time t _u to be measured
against

The relationship [Formula] is determined in advance with respect to the temperature change of the fluid to be measured. The fluid to be measured, the ultrasonic transmitter/receiver mounting material, the material of the piping, the geometric shape, and the temperature change range can be known in advance once the target plant where the ultrasonic flowmeter will be installed is determined, so it is easy to actually install the ultrasonic flowmeter in the plant. Even without installing and measuring, t _u can be calculated in advance.

The relationship with [Formula] can be found. From the relationship between the two obtained in this way, constants A and B that satisfy the following equation are determined. That is, t _u and

The relationship with [Formula] is approximately within the permissible error range and is a straight line, which can be obtained from the slope and intercept of this straight line. Using the constants A and B obtained in this way, the fluid flow velocity can be determined by the following equation, V=A/(t _u −B) ² △t ...(8) In equation (8), By using A and B, highly accurate output temperature correction corresponding to temperature changes of the fluid to be measured can be realized. A specific configuration for implementing equation (8) is the output temperature correction calculation section 7 shown in FIG. 2, and FIG. 3 shows the detailed configuration of the output temperature correction calculation section 7. In FIG. 3, it is clear that the amplification degree determined by the constant A in equation (8) is adjusted for the ultrasonic propagation time difference signal 8 in the amplification adjuster 71. The method of the present invention can also be applied to an ultrasonic flowmeter in which the ultrasonic transmitter/receiver mounting members 3a to 4b shown in FIG. It has the same effect as the example. Furthermore, in the above embodiment, the amplifier adjuster 71 in FIG. 3 was provided before the divider 74;
It may be provided after 4. As described above, according to the present invention, it is possible to realize temperature correction with a very simple function with high accuracy even when the temperature change of the measured fluid with respect to the output of an ultrasonic flowmeter is quite large. It is possible to provide a highly accurate ultrasonic flow meter even in cases such as plants where the temperature of the fluid to be measured changes over a wide range depending on the plant operating conditions.

[Brief explanation of drawings]

FIG. 1 is a functional block diagram showing the operating principle and measurement principle of a conventional ultrasonic flowmeter, FIG. 2 is a functional block diagram showing an ultrasonic flowmeter according to an embodiment of the present invention, and FIG. FIG. 2 is a detailed functional block diagram showing in more detail one function in the functional block diagram of FIG. 1a, 1b, 2a, 2b... Ultrasonic transmitter/receiver,
3a, 3b, 4a, 4b... Ultrasonic transmitter/receiver mounting member, 5... Piping, 6... Ultrasonic flowmeter circuit section,
7... Output temperature correction calculation unit, 8... Ultrasonic propagation time difference signal, 9... Ultrasonic propagation time signal, 71...
Amplification regulator, 72...Bias circuit section, 73...
Squarer, 74...divider. In addition, in the figures, the same reference numerals indicate the same or equivalent parts.

Claims (1)

[Claims] 1. In an ultrasonic flowmeter that measures the propagation time and propagation time difference of ultrasonic waves in a fluid to determine the flow velocity and flow rate of the fluid, a bias circuit section that subtracts or adds a constant value from a propagation time signal. , a squarer for squaring the bias circuit output, and a divider for dividing the propagation time difference signal by the squarer output. 2. The ultrasonic flowmeter according to claim 1, wherein a constant bias value that is subtracted from or added to the propagation time signal is determined from B according to the following equation. d; Internal diameter of the fluid pipe to be measured θ; Angle of incidence of ultrasonic propagation in the pipe Co; Speed of ultrasound sound in the fluid to be measured tu; Total propagation time from ultrasonic transmitter to ultrasonic receiver A, B: Output temperature correction coefficient.