SU1462114A1 - Device for graduating ultrasonic flowmeters - Google Patents

Abstract

The invention relates to instrumentation engineering and can be used in various areas of the national economy for measuring fluid flow. The aim of the invention is to improve the accuracy of calibration by eliminating systematic measurement error. The device contains a flow transducer 1, consisting of two electroacoustic transducers 2 and 3. The measurement direction switch 5 directs the radiation along or against the flow. The device operates in two modes: Measurement and Graduation. In the case of operation in the Measurement mode, the delay time of the signals in block 8 of the controlled delay is maintained. In the Graduation mode, using the switch 10, the discrete change of the delay time and the monitoring of the repetition period of the signals in the circuit are performed using a periodometer. The controllable delay unit 8 consists of a negative-feedback shock excitation generator, which includes a differential amplifier, a delay line, a variable delay time line, and a delay time switch. 2 silt no. Ff with (/)

Description

114

The invention relates to instrumentation and can be used 4 different areas of the national economy for the calibration of liquid flow meters.

The purpose of the invention is to increase the accuracy of the calibration by eliminating the systematic measurement error.

FIG. 1 is a block diagram of a calibration device; 2, a lock diagram of a controllable delay unit.

i The device contains a flow transducer 1 consisting of two electro-acoustic transducers I and 3 installed on the supply pipeline 4, a radiation control switch 5, a driver. 6 1 | mpulsov and a generator 7, a controllable delay unit 8, a control unit 9 - and, switch 10, periodometer 11 ijr output device 12, as well as constant voltage source 13 to which the second input of the switch 10 is connected.

i Controllable delayed unit 8 contains a shock excitation generator 14, made according to a scheme with delayed negative feedback and consisting of a differential amplifier, a delay line 16, a time line 17 with variable delay time and a junction switch 18. , counter 19 pulses and switch 20 operating mode. To control the difference in the delay time, a periodometer 11 is connected to the output of the controllable delayed unit 8.

The device works in two modes - presses.

In Measurement mode, switch 10 is in the second or third position. At the same time, the control input of the device 8 of the controlled delay is supplied either with a constant voltage (a logical 1 signal) or zero voltage (a logical O signal), which remain unchanged during the measurement and provide a constant signal delay time block 8 delay.

In the Graduation mode, the control input of the delay unit 8 is connected via a switch 10 to the output of the control unit 9.

In the Measurement mode, the device operates as follows.

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0

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five

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five

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five

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42

Under the action of a pulse produced initially by the generator 7, the device circulates pulses around the depi: radiation direction switch 5, electrical converters 2 and 3, switch 5, driver 6, controllable delay unit 8, pulse generator 7 operating in a synchronized mode, and etc. The direction of propagation of the probe pulses in the primary converter 3 is determined by the state of the switch 5 controlled by signals from the control unit 9. The periods of pulses following the flow and against the liquid flow depends on the propagation time of the probe signals in the converter 1 of the flow rate and the delay time in the electronic elements of the flow meter

(C + VsineyHSse 2 -} + t5i + t - tftg-Ht. + Tg,

  (c vSine) cose - - tfe + t -t-tg, (. 1)

where T, -, T2 are the periods of pulse following at the input of the generator 7;

D is the diameter of the pipeline; C, 0 - speed and angle ultrasound in fluid;

V - cKopoQTb liquid; tj. -.time of ultrasound propagation in the walls of the pipeline 4;

Hz

t 2 - the delay of the pulses in

electroacoustic transducers x 2 and 3 during their propagation along the current and against the fluid flow;

 -51 -52. delay, pulses in the switch 5, emitted from the flow and against the flow of the liquid;

tg, t-f, tg are the impulse delay, respectively, in the former 6, the control unit 8, my delay, and the generator 7.

The difference between periods 1 and T is proportional to the speed and flow rate of the liquid. 14, measured by output device 12

IB. ,, К (,) -K (, - but,) +, (2)

,., - t2.3; At5 t52-ty ,, where I 8 OUT Flow meter reading;

K - conversion factor

output device 12; itq is the asymmetry value of the flow transducer 1, caused by the non-identity of the transducers 2,3, as well as noise signals;

Etty is the asymmetry value of the switch 5, caused by non-identical conditions for the passage of multidirectional signals through it; - the error of the output device 12.

The last three terms in expression (2) are the error in measuring the flow meter.

To correct the measurement result, the flow meter is switched to the Graduation mode and the flow rate of the fluid is set to zero, for example, shut off the pipeline. With the help of valves,. and the switch 10 is set to the first position. In this mode, the delay time of the pulses in the controllable delay unit 8 depends on the direction of radiation of the probing signal: if the output of the control unit 9 is a logical O signal (the probing signal is emitted over the stream), the delay of the pulse is shorter than when a logical 1 signal is applied.

Thus, with the help of a controllable delay unit, the

the effect of a moving fluid on the period of circulation of pulses in the flow converter 1, and with an appropriate choice of the parameters of block 8, the delay difference created by it can be recalculated into an equivalent value of the velocity of the fluid in the pipe and pipeline

V l; Efia,) i

h 2Dtg 0

(3)

where is the simulated value of velocity. these liquids;

l g

 H Pbm delay in block 8. accordingly for pulses,

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emitted upstream and downstream. The operator manually changes the delay time t and, after taking the corresponding meter readings, determines the calibration characteristic of the flow meter, which is then used to calculate the systematic error at various points on the Ieb scale, (Vu) 1 uIeMx f (Vu) (4) where f (V) - dependence of indications

flow meter from simulated fluid velocity / (calibration characteristic);

 -bykh systematic error of the flow meter; K is the nominal conversion coefficient of the flow meter (passport value).

Subtracting from the previously obtained (or after calibration) measurement results the systematic error filftbix, we obtain the corrected measurement result of increased accuracy.

The controllable delay unit 8 operates as follows. .

At the moment the input pulse counter 19 is supplied to the stationary RV, it is set to the zero state. In this case, the blocking voltage is removed from the generator. 14 of the shock excitation, which, from a strictly defined phase, begins to produce a pulsed voltage applied to the equal input; counter 19, pulse. After the arrival of m-pulses at its output, a positive voltage drop is formed, which is an output signal and is delayed relative to the input pulse for a time

t.e, (m-H) to, - tg., (m + l) t, + t ,, J, (5) where m is the capacity of the counter,, 2 ...,; 1 is a fractional number that takes into account the initial phase of the oscillations of the shock excitation generator 14;

01 RIOD oscillations of a shock excitation generator for a control signal;

to the logical

one.

Oh and logical

514

 the delay time of the propagation of the signal in the counter 19,

At the same time, the voltage from the output of the pulse counter 19 is applied through the -switch 20 of the operating mode to the blocking input of the shock excitation generator 14 and the generation of the pulses stops until the next input pulse arrives

To calibrate the controllable delay unit 8, a zero potential is applied to the blocking в input of the generator 14 using the switch 20 and the generator 14 begins to generate a continuous sequence of pulses with a repetition period depending on the control signal and equal to t and tgj. Measuring the periods of pulse following by a periodometer 11, determine the difference in delay times.

At, (m-H) (t,. (6)

In order to ensure the stability and uniformity of the initial phase of the oscillation institute and the number 1, the shock excitation generator 14 is made according to a scheme with delayed negative feedback. Its initial phase is strictly equal to zero, if the reading is conducted from the negative front, and is equal to Jf when the phase is counted from the positive front. However, if the counter 19 at the counting input responds to the negative front, the value 1 in expression (6) is zero, otherwise, 5. The generation and timing of the pulses is controlled by applying a control signal to the 1 & switch, which switches the outputs of the delay line 16 and 17. By varying the delay time of the delay line 17, the difference in delay times required for calibration is created.

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Claims (2)

1. A device for calibration of ultrasonic flow meters, containing a primary flow transducer, including two electroacoustic transducers installed A controllable delay unit connected between the output of the pulse former and the generator input, characterized in that, in order to increase the calibration accuracy by eliminating systematic error, it is additionally entered a periodometer, a mode switch and a control unit, the periodomer input being connected to the output of a controllable delay unit, the control input of which is connected to the output of the mode switch, its first: the input is connected to the output of the control unit and the input of the switch of the radiator, and the second and third inputs are connected to a constant voltage source, with this, the input of the control unit is connected to the output of the driver. 2. The device according to claim 1, on. t l and, in particular, that the unit of the delay is tuned in the form of series-connected shock excitation generator, counter and switch, the output of which is connected to the input of the shock excitation generator. 15 Vmd 19 Output 1H Lh go -BUT Fie.2