RU2364841C1 - Method for measurement of liquid level - Google Patents

Abstract

FIELD: physics, measurements.

SUBSTANCE: invention is related to metering equipment and may be used for measurement of liquid levels in closed reservoirs. Time is measured for distribution of acoustic wave radiated by reversible ultrasonic converter (radiator-receiver), which is installed on cover of reservoir well at preset (reference) distance from upper limit of liquid level measurement range, to limit of mediums interface and back (the main reflected signal T₁), and time of acoustic wave distribution along the way: radiator, mediums interface, upper covering of reservoir back to interface of mediums and to ultrasonic converter (re-reflected signal T₂), and measured liquid level is calculated according to the following formula:

,

where L₀ is reference distance.

EFFECT: higher accuracy of level measurement during variation of parametres of gas medium above liquid: temperature, pressure, composition, etc, and elimination of dead zone inherent in acoustic level metres.

2 dwg

Description

The present invention relates to measuring technique and can be used to measure the levels of liquid media in closed tanks in the utilities, petroleum industry and transport.

Widely known methods for measuring the level of liquids by the method of acoustic location, when measured the propagation time of an acoustic wave from the emitter to the interface between media and vice versa and the distance is determined by the formula

L _x = V _z T / 2,

where V _z is the speed of sound, T is the propagation time of the ultrasonic wave in the forward and reverse directions.

The disadvantage of this method and its implementing devices is the dependence of the ultrasound speed on the parameters of the gaseous medium above the liquid: temperature, pressure, composition, etc., which leads to an additional measurement error.

To eliminate this drawback, a method for correcting the speed of propagation of an acoustic wave by the measured temperature of the gaseous medium of propagation of an acoustic signal in a location process is used. Using this method complicates the device and takes into account only one destabilizing factor.

Closest to the claimed technical solution is the method described in the patent of the Russian Federation for the utility model "Electronic-acoustic device for measuring the liquid level" measurement [1], using the main reflected signal and the signal reflected from the reference reflector, calculating the current propagation velocity of the sound wave and calculating fluid level according to the corresponding formula.

The technical result of the invention is to increase the accuracy of measurement, eliminate errors with changing parameters of the gas medium above the liquid: temperature, pressure, composition, etc., and provide level measurement over the entire height of the tank.

This is achieved by the fact that in the method of measuring the liquid level, which consists in emitting a sounding acoustic pulse and receiving a reflected signal from a medium section, according to the invention, the propagation time of an acoustic wave emitted by a reversible ultrasonic transducer (emitter-receiver) is measured, which is set at a predetermined (reference ) distance from the top of the liquid level measurement range to the boundary between the media and forth (main reflected signal T _1), and extends the time of acoustic waves on the way: the emitter section mediums overlap the upper reservoir back to the media section and to the ultrasonic transducer (Backlight signal T _2), and calculating the measured liquid level from the formula

,

,

where L ₀ is the reference distance.

From the obtained expression it follows that the measured parameter — the level of separation of the gaseous and liquid media — does not depend on the propagation velocity of the acoustic wave in the gas medium.

Figure 1 presents the electrical functional diagram of an ultrasonic level gauge that implements the proposed method for measuring the liquid level.

The device contains a reservoir (measurement object) 1, a well with a cover 2, a reversible electro-acoustic transducer (emitter-receiver) 3, and a series-connected generator of a probe pulse train 4, a mode switch of the electro-acoustic transducer 5, amplifier 6, a filtering and decoding unit for reflected signals 7, measurement unit 8, control device 9, synchronizing the operation of all blocks of the level gauge, information processing device 10, indicator 11.

Figure 1 also shows the propagation path of the main acoustic wave 13 and the reflected wave 12.

The proposed method for measuring the liquid level is implemented as follows.

The excitation of the electro-acoustic transducer 3 in the radiation mode and the formation of the probe pulse is carried out using a generator of bundles of probe pulses 4, the parameters of which are frequency, the number of pulses in the packet are set in advance. The operating mode "radiation - reception" is carried out using the switch 5.

Out of the whole variety of propagation paths of emitted and reflected acoustic vibrations, two are used in this case, indicated in Fig. 1 as 12 and 13.

The propagation time of the signal along path 13 is determined by the equation

where L ₀ is the predetermined (reference) level value, defined as the distance between the electro-acoustic transducer and the upper level of the tank, V _z is the acoustic wave propagation velocity at the time of measurement.

The propagation time of the signal along path 12 (see figures 1, 2) can be determined from the expression

The reflected signal received by the electro-acoustic transducer 3 after time T ₁ and reflected after time T _{2 is} amplified by the amplifier 6 and fed to the filtering and decryption unit of the reflected signal 7, where the signal is analyzed by the frequency (period) and number of pulses in the packet with the same period.

According to the selected pulses (see figure 2), limiting the time intervals T ₁ and T ₂ , the measuring unit 8 determines the intervals T ₁ and T ₂ , and the block 10 processes the received information.

The solution of the resulting system of equations (1) and (2)

relative to L _x will be determined by the expression

.

.

The liquid level in the tank L _W relative to the bottom can be determined by the formula

L _W = L _max -L _x ,

where L _max - the maximum possible value of the measured liquid level in the tank.

The implementation of computational operations is possible both analog and digital means. However, it is obvious that the use of digital technologies for processing a temporary signal is, in this case, preferable.

The measurement result is transmitted to the indicator 11. The operation of all devices and blocks of the level gauge is synchronized by the control device 9.

Using the reference value of the level L ₀ allows you to determine the current velocity of propagation of ultrasound, which eliminates the influence of disturbing influences; the installation of an electro-acoustic transducer at a given distance in the well eliminates the dead zone of the acoustic emitter and provides level measurement over the entire height of the tank, increasing the propagation path of the acoustic wave at a certain resolution of the device can also improve the accuracy of measurement.

The practical implementation of the ultrasonic level transmitter that implements the proposed method, based on the PIC18F2620 single-chip microcontroller, showed rather high metrological characteristics when measuring in closed and open sewer and water intake stations. In particular, with a level measuring range of 6 m, a resolution of 10 mm was obtained, and the main and additional error components in the entire temperature range from -25 ° C to + 25 ° C and the corresponding humidity and air pressure did not exceed the value of the least significant discharge.

The source of information

1. Certificate for utility model RU No. 53001. Electronic-acoustic device for measuring liquid level. Borminsky S.A., Skvortsov B.I. - published: 04/27/2006, Bull. No. 12.

Claims (1)

A method of measuring a liquid level, which consists in emitting a sounding acoustic pulse and receiving a reflected signal from a medium section, characterized in that the propagation time of an acoustic wave emitted by a reversible ultrasonic transducer (receiver emitter) is measured, which is mounted on the reservoir well cover at a predetermined (reference) distance from the top of the liquid level measurement range to the boundary between the media and forth (main reflected signal T ₁₎ and the propagation time of an ultra acoustic wave along the path: an emitter section mediums overlap the upper reservoir back to the media section and to the ultrasonic transducer (Backlight signal T _2), and calculating the measured liquid level from the formula

where L ₀ is the reference distance.

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