JPS6244626A - Calibrating method for transmission type ultrasonic flowmeter - Google Patents

Abstract

PURPOSE:To easily calibrate a transmission ultrasonic flowmeter after its installation in a plant by alternating two probes for calibrations in transmitting and receiving ultrasonic pulses and obtaining a propagation time corresonding to that in reference flow velocity measurement artifically. CONSTITUTION:While two couples of probes 11 and 12, and 13 and 14 for calibration are set at the same distance, an ultrasonic flowmeter is put in operation and a zero adjustment is made by the zero adjusting device 7a of an arithmetic circuit 7 so that the output signal from the arithmetic circuit 7 indicate a zero flow velocity. Then, a computing element 16, a constant input setter 17, and a probe positioning mechanism 18 are provided and a reference flow velocity V, the distance L between probes, an angle theta, and acoustic velocities C and C0 in stationary gas are inputted to the computing element 16. Then, the distances L10 and L20 between the probes 13 and 14, and 11 and 12 are calculated from equations I and II and arithmetic values are used as command signals to control a probe positioning mechanism 18. Thus, the distance L10 and L20 are determined automatically and a calibrating device is connected to downstream-side probe receiving circuits 3 and 4 of the ultrasonic flow meter to make calibrations.

Description

[Detailed description of the invention] "Industrial application field" The present invention relates to a method for calibrating a transmission type ultrasonic flowmeter.

``Prior art'' Transmission type ultrasonic flowmeters are well known as instruments for measuring flow velocity, and in particular, with the recent development of ultrasonic flowmeters for gases, the range of their use has been greatly expanded, and even in the steel industry M It is often used to measure the flow velocity of gas, B gas, or air.

Here, the principle of a transmission type ultrasonic flowmeter will be explained with reference to FIG.

In FIG. 2, the propagation time t1 of the ultrasonic pulse transmitted from the downstream probe 2 to the upstream probe 1 is +11
It is expressed by the formula.

■ (In formula 11, L is the distance between the downstream probe 2 and the upstream probe l, C is the propagation velocity of the ultrasonic pulse in stationary gas, ■ is the velocity of the fluid, and θ is the upstream probe 1 This is the angle between the line connecting the downstream probe 2 and the flow velocity direction.

Further, the propagation time t2 when an ultrasonic pulse is transmitted from the upstream probe 1 to the downstream probe 2 is expressed by equation (2).

t2-=□・・・・・・・・・・・・・・・・・・
-(2) C+Vcosθ Therefore, the flow velocity V is determined by equation (3).

The above is the principle of the transmission-type sonic flowmeter.In reality, ultrasonic pulses are periodically transmitted alternately from the downstream probe 2 or the upstream probe 1 until the pulses are input to the opposite probe. Time t1. t2 is measured, and the flow velocity V is determined by electrical calculation.

FIG. 3 is a block diagram of a transmission type ultrasonic flow needle,
A wave transmitting/receiving circuit 3.4 for upstream and downstream probes is connected to the upstream probe 1 and a downstream probe 2, respectively. l.

(Ultra) where the ultrasonic pulses are alternately input to 2)
□2.714, y-yo. , □7.7. 1. Send a switching clock pulse to the circuit 5, and send an ultrasonic pulse to the upstream and downstream probe 1 in accordance with this switching clock pulse.
.

To explain flow velocity measurement using the ultrasonic flow needle shown in FIG. 3, first, a switching clock pulse is sent from the upstream/downstream switching clock pulse generating circuit 6 to the ultrasonic pulse generating circuit 5.

The ultrasonic pulse of the ultrasonic pulse generation circuit 5 is transmitted from the upstream probe l via the upstream probe transceiver circuit 3 at the timing of the low level of the clock pulse, for example, and is received by the downstream probe 2. .

The pulses received by the downstream probe 2 are input to the ultrasonic pulse generation circuit 5 via the downstream probe transceiver circuit 4, and the ultrasonic pulse generation circuit 5 measures the propagation time t2.

For example, at the high level timing of the clock pulse, as shown by the broken line in FIG. Probe transceiver circuit 3
The signal is input to the ultrasonic pulse generation circuit 5 via the ultrasonic pulse generation circuit 5, and the propagation time t1 is measured in the ultrasonic pulse generation circuit 5.

Then, in the arithmetic circuit 7, ti
+, Flow velocity ■ is calculated from t2.

"Problems to be Solved by the Invention" By the way, with transmission-type ultrasonic flow needles, once installed in a plant, there is no means to calibrate the measurement accuracy, so the design accuracy is always maintained. There was a problem that the reliability of flow rate measurement was poor, and the plant had to be operated with the belief that this was the case.

"Means for Solving the Problems" The present invention is intended to solve the problems of the transmission type sonic flowmeter as described above.

That is, in the transmission type sonic flowmeter of the present invention, each pair of two sets of calibration probes are installed at a distance corresponding to the propagation time of the ultrasonic pulse when measuring the reference flow velocity, and the transmission of the ultrasonic pulse is performed. The gist of the present invention is to alternately switch between the two sets of probes to receive waves, thereby obtaining a simulated propagation time equivalent to the time of standard flow velocity measurement.

The method of the present invention will be explained below.

The present invention focuses on the fact that if the propagation times t+a and tm of ultrasonic pulses corresponding to the flow velocity Vo can be created in a simulated manner, a transmission type sonic flowmeter can be calibrated.

That is, in order to obtain the propagation times tIl and t2I corresponding to the predetermined flow velocity VO consisting of the above equations (11 and (2)) in a stationary gas, similarly, for the distances L+a and IJ given by, It can be seen that it is sufficient to make the upstream probe and the downstream probe face each other.

FIG. 1 is a block diagram of the method of the invention.

This means that the first
A pair of calibration probes IL 12 of the set are installed with their facing distance being j, and a pair of calibration probes 13 and 14 of the second set are installed with their facing distance being LIl, and upstream/downstream switching clock pulses are generated. Switching black 7 from circuit 6
pulse, ultrasonic pulse.

By inputting it to the generation circuit 5 and also inputting it to the transmission/reception switching circuit 15, activating the transmission/reception switching circuit 15, and switching the signal lines to the two sets of calibration probes 11.12 and 13.14. As if flowing) □３
□7°, ゎ, 6.6o, 5o, Kawa 3yu calculation circuit 7.

Here, to explain the function of the transmission/reception switching circuit 15, at the timing of the high level of the clock pulse mentioned above, the analog switches 15a and 15b are turned on, and the ultrasonic pulse of the ultrasonic pulse generation circuit 5 is turned on. As shown by the dashed line in Figure 1, the downstream probe transceiver circuit 4
, analog switch 15a1 second set of calibration probe 1
3, 14, the signal is input to the ultrasonic pulse generation circuit 5 via the analog switch 15b and the upstream probe transceiver circuit 3, and the propagation time tII is measured.

Also, at the timing of the low level of the clock pulse mentioned above, NO? Analog switch 15 via circuit 15c
d, 15e turns on, and the ultrasonic pulse generation circuit 5
As shown by the two-dot chain line in FIG. 1, the ultrasonic pulse of
The signal is input to the ultrasonic pulse generation circuit 5 via the first set of calibration probes 11 and 12, the analog switch 15e, and the downstream probe transceiver circuit 4, and the propagation time is measured.

By doing this, the distance between the pair of probes 11.12 of the first set corresponds to 1 - and the second
The received pulses are returned alternately with a propagation time Lm corresponding to the distance Lm between the pair of probes 13.14, and therefore propagation times t, ..., t2 corresponding to the flow velocity V are given in a simulated manner. It turns out.

"Operation" The method for calibrating the ultrasonic flowmeter will be explained based on FIG. 1.

First, the distances between each pair of calibration probes 11, 12 and 13, 14 are made equal, and the ultrasonic flowmeter is operated so that the output signal from the calculation circuit 7 at this time indicates zero flow velocity. Next, zero adjustment is performed by the zero adjuster 7a of the arithmetic circuit 7.

Next, the flow velocity V near the maximum range of the ultrasonic flowmeter.

The distances LII and IJ between each pair of calibration probes 13.14 and 11.12 corresponding to (4), (
5) Two sets of calibration probes 13, each pair
．． Set the distance between question 14 and 11.12 to LLI, IJ.

In this state, operate the ultrasonic flowmeter and adjust the span adjuster 7 so that the output of the arithmetic circuit 7 at this time becomes the reference flow rate ■0.
Perform span adjustment using b.

Using this method, the ultrasonic flowmeter can be calibrated for any flow rate by simply setting the calibration probes 13.14 and 11.12 at the distance -, Lll corresponding to the flow rate V for which calibration is desired. I can do it.

Note that when the flow velocity is zero, LIl-La may be used.

"Example" LLI corresponding to the flow rate Vo in the method of the present invention described above
, Lll, and thereby automatically calculate the distance between each pair of calibration probes 13.14 and 11.12, as shown in FIG.
, constant input setting device 17 , and probe positioning mechanism 18
The constant input setting device 17 inputs the reference flow velocity V, the distance between the probes, the angle θ, and the speed of sound in stationary gas C5Co into the calculator 16, and sets two sets of calibration probes for each pair. 13.14 questions and distance LL1 between 11°12
．． By calculating Lxa based on equations (4) and (5) and controlling the probe positioning mechanism 18 using this calculated value as a command signal, each pair of two sets of calibration is performed via the probe positioning mechanism 18. The distance between probes 13.14 and 11.12 can be automatically set to Lm, [J.

That is, each pair of two sets of probes 11, 12 and 1
3.14, the wave transmission/reception switching circuit 15, the arithmetic unit 16,
Calibration can be performed extremely easily by simply connecting the calibration device consisting of the constant input setting device 17 and the probe positioning mechanism 18 to the upstream and downstream probe transceiver circuits 3.4 of the ultrasonic flowmeter. .

Furthermore, for example, to explain the case of performing three-point calibration of an ultrasonic flow meter, 0% of the measurement range of the ultrasonic flow needle
, 50%, and 100%, and the flow velocity for each propagation time is V m , V s
o + V 1011, and the output signals of the arithmetic circuit 7 at this time are Ycm, Yso, Ymo (however, these are the outputs when the ultrasonic flow needle is operating correctly).

Distance LLI between calibration probes 13.14 and 11.12 to create propagation times for these flow velocities.
IX1 and Iayr, L (experiment and Ia, io, -
Tao and IJJoo are given as follows from equations (4) and (5).

(θ %) (50χ) (100χ) Set two pairs of calibration probes 13.14 and 11.12 at these distances, operate ultrasonic flowmeter 1, and measure their respective outputs. Measure.

If the respective outputs are Yoo', Y5a', and Yyo', then, of course, when the ultrasonic flow-needle is operating normally and there is no error, YIl11'''''YoaI Y5@' = Y2O Y+oo' Y-, and if an error occurs, arithmetic circuit 1
Perform zero adjustment and span adjustment in step 7.

"Effects of the Invention" As described above, according to the method of the present invention, it is possible to easily calibrate a transmission type ultrasonic flowmeter after installation of a plant, which was difficult to perform in the past. This has the remarkable effect of making it possible to control the accuracy of the ultrasonic flowmeter and further expanding the range of application of the ultrasonic flowmeter.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of the method of the present invention, FIG. 2 is a diagram explaining the principle of a transparent type B ultrasonic flowmeter, and FIG. 3 is a block diagram of a transparent type B sonic flow meter. L... Upstream probe, 2... Downstream probe, 3
... Transmission/reception circuit for the upstream probe, 4... Transmission/reception circuit for the downstream probe, 5... Ultrasonic pulse generation circuit,
6... Upstream/downstream switching clock pulse generation circuit, 7... Arithmetic circuit, 7a... Zero adjuster, 7b... Span adjuster, 11.1... First set of pair of calibration probes ,
13.14... Second set of pair of calibration probes, 15
... Transmission/reception wave switching circuit, 16... Arithmetic unit, 17...
Constant manual setting device, 18... Probe positioning mechanism "'<9/"

Claims (1)

[Claims] In a transmission type ultrasonic flowmeter, two pairs of calibration probes are installed at a distance corresponding to the propagation time during reference flow velocity measurement, and the transmission and reception of ultrasonic pulses are performed by the two sets of probes. A method for calibrating a transmission type ultrasonic flowmeter, characterized in that the transmission time is alternately switched to obtain a propagation time equivalent to a reference flow velocity measurement in a simulated manner.