SU932240A1 - Ultrasonic flow meter - Google Patents

Description

(5) ULTRASONIC FLOW METER

I

The invention relates to instrumentation, in particular to the technique of measuring the flow of liquid media.

Ultrasonic time-frequency flow meters are known based on maintaining a constant ratio of the transit time of an ultrasonic pulse along and against the flow to the pulse period of the corresponding generator. The flow meters contain two controlled pulse generators connected via piezo transducers with keys, a frequency control circuit and a measure of the difference in the frequency of the till.

A disadvantage of flow meters is low measurement accuracy.

The closest in technical essence to the present invention is an ultrasonic single-channel flow meter containing two controlled oscillators, the outputs of which are connected to a frequency difference meter and the inputs of the first key, the output of which is through;

the trigger, the probe pulse shaper, the second key, is connected to the inputs of the reversible transducers, and then via the third key, the amplifier shaper, the time selector, the fourth key, and the integrators to the control inputs of the generators. In addition, the device contains a switch that controls the inputs of the keys 2.

The nominal static characteristic of an ultrasonic time-frequency flow meter is: 2m f 2t3-C

-) V,

(1Ci)

F l

15

where F is the output frequency of the flow meter;

L is the base length of the acoustic channel;

m is the division ratio of the frequency divider of controlled oscillators;

C is the propagation velocity of the ultrasonic wave in the measured fluid; V is the flow velocity averaged along the length of the acoustic channel; delay time in blocks, membranes and pockets of the flow meter. Under operating conditions, the ultrasound velocity (C) may differ for some reason from the calibration value, which causes a change in the static characteristic - 2m f - (1 dS) V (2) As can be seen from ( 2) the presence of the dS term causes an increase in measurement error 2. A disadvantage of the known flow meter is the low measurement accuracy due to the dependence of the measured parameter on the measured liquid. The purpose of the invention is to improve the accuracy of flow measurement. The goal is achieved by the fact that the device is equipped with a divider, four decoders and a period-time converter, the decoder inputs are connected to the output of the first key through a divider, the output of the first decoder is connected to the input of the probe pulse generator, and the outputs of the second and third decoders are connected to the trigger inputs, and the fourth decoder output is connected to the switch input and the divider setting input. FIG. 1 is a block diagram of a flow meter; in fig. 2 - time diagrams. The flow meter contains two controlled oscillators 1 n 2 connected via the first 3 and second A keys with piezoelectric transducers 5 and 6. The frequency control circuit of the generators is designed as a trigger 7 with a counting input and a temporary selector 8, the measurement input of which through the third key 9 is connected to the piezoelectric transducers, and the outputs are connected via the fourth key 10 and the integrators 11 and 12 to the generators 1 and 2. The device also contains the former-13 probe pulses, the amplifier-former 1 of the received signals, the meter 15 and the switching device 16. Furthermore, in the entrance of the flowmeter m divider 17, deshif tors 18-21, as well as the time-period of transducer 22. The apparatus operates as follows. The switch signal (FIG. 2, plot 2 a) switches keys (3, and 10), providing measurement in one direction, for example, along a stream. Generator 1 pulses through a key are fed to register 17, which is reset to zero in the initial state (Fig. 26). When the K code is reached, the decoder 18 outputs a signal to the converter 22 (Fig. 2, d), which after a certain time generates a signal ( Fig, 2, d). The latter through the driver of the excitation pulses 13 and the key 4 is fed to the piezoelectric transducer 5. After passing through the measured liquid, the received signal (Fig. 2, k) through the key 9 is fed to the amplifier-driver 14 and further to the input of the time selector 8 as a measuring signal . The reference signal of the selector are the pulses of the trigger 7 (Fig. 2, and), which are formed as follows. After reaching code 1 in the register, the decoder 19 signal (Fig. 22, e) changes the state of trigger 7 (Fig. 2, i), and after reaching the code, the signal of the decoder 20 (Fig. 2, c) is flip- off. The trigger is reset (Fig. 2, i). The voltage drop received from the trigger serves as a reference signal for the selector 8. The process described above in the flow mode is performed once, since this principle of the flow meter (the formation of only one ultrasonic pulse in the measured fluid in each radiation mode) reduces the time measuring the flow meter, which causes a decrease in its error due to fluctuations in the physical properties of the measured liquid. The use in the proposed device of one divider with several decoders simplifies its functional diagram and design in comparison with the use of several parallel operating dividers. The control signal to the input of integrator 12 depends on the temporal position of the reference and measurement signals of the selector. The control of the pulse period (T) of the generator by the output voltage of the integrator is carried out until the condition t 1 (m - 1) Tr.,. 1- L 1 C + V where T-1 is the period of the pulse generator 1. When the code n is reached in the register, the decoder 21 outputs a signal (FIG. 2, g) to the switching device 16 for ne10

switching the radiation direction and the positions of the keys 3, 9 and 10 (Fig. 2, a) and to the register 17 to reset it to zero.

When operating in the upstream mode, the pulse period of the generator 2 is changed until the condition

tn (m - 1) 1; t, L (4)

1 С - V where Tn is the pulse following period,

generator 2. The meter 15 of the frequency difference allocates the difference frequency of the generator 1 25 P - - 2 (t - 1), g. T T7 - 1 1 As can be seen, expression (5) differs from (1) by the absence of a member, i.e. The readings of the proposed device will not depend on the change in the velocity of the ultrasonic wave relative to its graduated value, which leads to an increase in the accuracy of flow measurement. Thus, an increase in the measurement accuracy is achieved by introducing a converter 22 into the flow meter, the parameters of which are chosen so that the probe pulse of the driver 13 advances the moment of change from that trigger 7 always by the same value equal to the total delay time of ultrasonic oscillations electron blocks, membranes, and a carriage of acoustic flowmeter heads (t). The value of t for each flowmeter instance can be determined with great accuracy, it remains almost constant under operating conditions. The purpose and principle of operation of converter 22 is determined from its functional purpose, which is to generate a pulse at a stable time t after receiving 9322 5

the cryogenic media and liquid metals, since it retains its characteristics determined during calibration, for example, on water.

Claims (2)

Invention Formula An ultrasonic flow meter containing two controlled oscillators, the outputs of which are connected to the frequency difference meter and the inputs of the first switch, are connected in series to the driver of the probe pulses. 06 of the signal from the divider 17. The magnitude of the given time t is related to the pulse period of the generators 1 and 2 by the expressions t (1 - K) Tj - t in the flux mode (6); t (1 - K) tjB radiation upstream mode (7). The proposed device can be widely used for measuring with high flow rate accuracy and a quantitative key, two reversible electroacoustic transducers, a third key, an amplifier-shaper, a time selector, a fourth key, the outputs of which through the first and second integrators are connected to the inputs of controlled generators, trigger, the output of which is connected to the input of the time selector, and a switch connected to the control inputs of the four keys, characterized in that, in order to improve the measurement accuracy, the devices The divider is equipped with four decoders and period-time converters, the decoder ports and the divider are connected to the first key, the output of the first encoder through the period-time converter is connected to the input of the probe pulse former, you have the second and third decoders connected to the trigger inputs, and the output the fourth decoder is connected to the input of the switch and the installation input of the divider. Sources of information taken into account in the examination 1. USSR author's certificate number 16233, cl. G 01 F 1/66, 1962. 2. USSR author's certificate No. 523285, cl. G 01 F 1/66, 197 (prototype;). 1 n t / 77/7 f t