JPS62257021A - Calibration of ultrasonic flowmeter - Google Patents

Abstract

PURPOSE:To enhance the measuring accuracy of the flow rate of a fluid, by calibrating an actually measured flow rate on the basis of the actually measured value and a planning value of the inner diameter of fluid flow piping and the actually measured value and planning value of the mount angle of the transmitting and receiving probe mounted on the aforementioned piping. CONSTITUTION:An upstream side probe 2 and a downstream side probe 3 are arranged to the wall of fluid flow piping 1 in opposed relationship so as to cross the pipe axis of the piping 1 at a required angle theta and alternately transmit ultrasonic pulses cyclically by a flow amount operator 4 and an apparent flow rate Qd' is operated on the basis of respective propagation times t1r, t2r required before pulses are inputted to the opposed probes. This value Qd' is multiplied by a flow rate correction value alpha represented by formula (wherein Dr and Dd are the actually measured value and planning value of the inner diameter of the piping and thetar and thetad are the actually measured value and planning value of a probe mount angle) by a flow rate correction operator to obtain a true flow amount Qr.

Description

DETAILED DESCRIPTION OF THE INVENTION "Field of Industrial Application" The present invention relates to a method for calibrating a Kawano-a flowmeter.

Conventional Techniques Ifi'' Conventionally, differential pressure flowmeters have been used to measure the flow rate of fluids such as gas in large-diameter pipes, but because the production cost of large-diameter throttle mechanisms is high, Recently, ultrasonic flowmeters have come into widespread use.

In order to measure the flow rate of the fluid flowing through the fluid distribution piping using an ultrasonic flow meter, as shown in Fig. Intermittent ultrasonic pulses are alternately transmitted from the upstream probe 2 facing the wall to the downstream probe 3, or from the downstream probe 3 to the upstream probe 2, and the pulses are sent to the opposing probe. Each propagation time t1. Measure the velocity of the fluid by electrical calculation from each propagation time 1++1*, calculate the cross-sectional average jt+ from the fluid velocity ~l, and multiply the cross-sectional area of the distribution f1 by 11). , I am finally looking for the flow rate.

"5 points to be solved by the invention" The propagation time t+, ta is the distance F between each probe 2.3
In order to indicate different values depending on the IL, each blow, '2.
When installing 3, consideration must be given to ensure that their mounting position and dimensions match the design values.

However, it is no exaggeration to say that in reality, it is almost impossible to make the mounting positional relationship and dimensions of each probe 2.3 exactly as measured values.

For example, see Section 12 below. As shown in , there is a difference of a1 between the designed value and the actual value.

Table 1 Therefore, it is not possible to measure the fluid flow rate in the bath.

"Means for Solving the Problems" The present invention has been made to eliminate the error in determining the fluid flow rate 111 caused by the ultrasonic meter due to the installation error as described above.

That is, the present invention is based on the actual measured values of the inner diameter of the fluid circulation pipe to which the transmitting/receiving probe of the ultrasonic flowmeter is attached and the mounting angle of the transmitting/receiving probe, and the measurement of The gist is to calibrate the actually measured flow rate using the correction value α obtained from the following formula based on the design value of the installation angle variation.

Here, Dr and Dd are the actual measured value of the pipe inner diameter and the setting i.
tfil! i, θr: 6 and θ(j: y) are actual measured values and designed values of the transmitting/receiving probe mounting claw.

Next, the calibration method of the present invention will be explained based on the measurement principle of an ultrahigh wave flowmeter (see Fig. 2).

Design (theoretical) propagation time Ltd when transmitting an ultrasonic pulse from the upstream probe 2 to the downstream probe 3
:! , +11.

(1) In formula (1), C is the propagation velocity of an ultrasonic pulse in a stationary fluid, and d in each symbol means a designed value.

Also, the designed (theoretical) propagation time t+ when transmitting an ultrasonic pulse from the downstream probe 3 to the upstream probe 2
d is expressed by equation (2).

On the other hand, the relationship between the designed linear average flow velocity Vd and the designed cross-sectional average flow velocity d is expressed as in equation (3).

V d −d xk・・・・・・・・・・・・・・・
・・・・・・・・・・・・・・・・・・・・・＋31(
3) In the formula, k is a conversion coefficient of the cross-sectional average flow velocity d to the line average flow velocity Vd.

The designed flow rate Qd is then determined by equation (4).

(4) In the formula, Dd is the designed inner diameter of the distribution v1.

Based on the above equations (1) to (4), equation (5) is obtained.

1 1-d πDd" On the other hand, when the distance uL between each probe 2.3, the Proso installation angle θ, and the white mud on the pipe l deviate from the design values, the true flow rate Qr and the apparent reduction amount QJ' is expressed by equations (6) and (7), respectively.

tIr ttr In formulas (6) and (7), r in each symbol has an actual value of 8.

t Each 7' lobe 2.3 from the installed state (8
) and (9) hold true.

Therefore, how many times should we multiply the flow rate in (1) to get the true flow rate? /itR? ! The positive value α is calculated as shown in 0@formula based on formulas (6) to (9).

"Example" Next, an example of the calibration method of the present invention for an ultrasonic flowmeter will be described based on FIG.

In FIG. 1, l is a fluid distribution pipe, 2 and 3 are
An upstream probe and a downstream probe 4 are arranged opposite to each other on the wall of the pipe 1 so as to intersect the pipe axis of the pipe 1 at a required angle θ, from the upper probe 2 to the lower part: A f
The hl l' Y wave pulse is alternately and periodically transmitted to the VI probe 3 or from the downstream probe 3:1 to the upstream probe 2, and each propagation time L1r + L1 until the pulse is input to the opposite probe. ``Based on (7) above.
This is a flow rate calculator that calculates the apparent flow Hqd' according to the formula.

5 is the apparent flow rate Q which is the output of the flow rate calculator 4.
d', the distribution is the real value of the inner diameter of l'I (A D r, and the true value of δP equation (6) '/& fR12?i positive operator to obtain the output corresponding to the quantity Q r It is.

In addition, in the present invention, in order to correct error factors, the flow rate ?
The actual JII value Dr of the inner diameter of the pipe l and the actual measured value θr of the mounting angle of each probe 2.3 are used as the setting values for the +li positive calculator 5, and the distance XI between each probe 2.3 is used.
Although the real III value of L is not used, it is based on the above (8)
This is because the relationship of equation (9) holds true.

In addition, the actual measured value Dd of the inner diameter of the arrangement fl and each probe 2.3
The calculated value may be set to the flow rate correction calculator 5 from the actual measurement value θr of the mounting angle.

Furthermore, it may be determined by actually measured values of the mounting angles of the respective probes 2 and 3.

"Effects of the Invention" As described above, according to the calibration method of the present invention, even if the inner diameter of the fluid distribution pipe and the mounting angle of the transmitting/receiving probe deviate from the designed values, the fluid flow rate can be very easily corrected to the true fluid flow rate. Therefore, the measurement accuracy of fluid flow rate using an ultrasonic flowmeter can be significantly improved.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the method of the present invention, and FIG. 2 is a diagram illustrating the principle of an ultrasonic flow needle. 1... Fluid distribution piping, 2... Upstream probe, 3
...Downstream probe, 4...Flow rate calculator, 5...
Flow rate correction calculator Figure 1

Claims (1)

[Claims] Actual measured values of the inner diameter of the fluid circulation pipe to which the transmitting/receiving probe of the ultrasonic flowmeter is attached and the mounting angle of the transmitting/receiving probe, and design values of the inner diameter of the pipe and the mounting angle of the transmitting/receiving probe. A method for calibrating an ultrasonic flowmeter, characterized in that the measured flow rate is calibrated using a correction value α obtained using the following formula. α=[(Dr)/(Dd)]^3×[(sin2θd)
/(sin2θr)] Here, Dr and Dd are the measured values and designed values of the pipe inner diameter, and θr and θd are the measured values and designed values of the transmitting/receiving probe mounting angle.