RU2123172C1 - Method and device to check level of liquid medium in reservoirs - Google Patents

Abstract

FIELD: metallurgy, chemical and petroleum refining industries. SUBSTANCE: acoustic radiator with two angles of feed of ultrasonic vibrations into wall of reservoir excites two types of ultrasonic waves: normal wave of needed mode and surface wave that propagate in parallel to plane of surface of checked liquid over perimeter of reservoir inside wall and over its outer surface. Acoustic receiver identical to radiator mounted at definite distance relative to radiator in zone of level check is employed to receive ultrasonic vibrations. Information on presence or absence of liquid medium at checked level is extracted by amplitude of normal wave. Correction of amplitude of normal wave with change of acoustic resistance of contact layer is carried out by amplitude of surface wave. Device for realization of method includes two acoustic converters, generator, measurement stage, two selective stages, two peak detectors, two delay units, two formers of gating pulses, comparator, coincidence circuit, counter, decoder, unit of analog keys, attenuator, summing unit, amplifier, source of reference voltage. EFFECT: increased reliability and precision of check. 2 cl, 2 dwg

Description

 The invention relates to techniques for controlling the technological parameters of liquid media in tanks for industrial production and can find application in metallurgical, chemical, oil refining, water treatment and other industries.

 There is a method of ultrasonic control of parameters of liquid media, for example, the liquid level in tanks, which consists in the fact that ultrasonic vibrations are periodically introduced into the tank wall along the normal to it in the level control zone, pulse signals and acoustic reverberation signals reflected from the opposite wall are received in the tank wall, emit the envelope of the reverberation pulses in a given time zone and judging by its amplitude about the presence of fluid at a controlled level [1].

 The disadvantage of this control method is the low accuracy and reliability of level control, since changes in the amplitude of the envelope of the reverberation pulses, which are used to judge the level when damping the wall with liquid, are insignificant and depend on the acoustic resistance of the contact layer between the acoustic transducer and the tank wall.

 There is another method of ultrasonic control of the liquid level in tanks, which consists in the fact that a longitudinal ultrasonic wave is introduced into the tank wall at an angle parallel to the surface of the medium in the level control zone, the trace speed of which along the input surface is set equal to the speed of a normal wave (Lamb wave) propagating in the wall, and after passing a fixed distance along the wall, the Lamb wave is received and its amplitude is used as an information signal about ram [3].

 The disadvantage of this method of controlling the liquid level, which reduces its reliability and accuracy, is the instability of the amplitude of the information signal when the wall thickness in the tank changes due to corrosion or exposure to aggressive media and the residual components of the liquid reagents overgrow.

 The disadvantages of the second method include low reliability due to the instability of the information signal as a result of changes in the acoustic resistance of the contact layer between the acoustic transducers and the tank wall.

 Closer (prototype) of the proposed method is the second analogue.

 The proposed method differs from the known method in that it simultaneously additionally excites a surface wave that does not experience attenuation when the tank wall is damped with liquid in the level control zone, receive it with the same acoustic receiver, attenuate the received input signal containing both waves, emit the surface wave amplitude in it, detect it and form a threshold signal whose value is stored, compare the amplitude of the surface wave with a threshold signal, and when it decreases, form a periodic a sequence of control pulses, the number of which is proportional to the decrease in the amplitude of the surface wave relative to the threshold signal and inversely proportional to the value of the initially introduced attenuation, direct the pulses to the attenuation circuit of the input signal and restore the amplitude of the information normal wave.

 The essence of the proposed method of level control is illustrated by the acoustic circuit in FIG. 1 and is as follows.

 Longitudinal ultrasonic vibrations (ultrasonic vibrations) are periodically directed to the wall of the tank with a controlled fluid medium at different angles α and β, which are excited using a generator and an acoustic transducer (emitter) mounted on the surface of the tank in the level control zone.

 The input angles α and β of the longitudinal ultrasonic ultrasound are chosen so that normal and surface waves are formed in the wall as a result of refractions on the external surface.

где
C₁ - скорость звука в волноводе акустического излучателя;
C_ф - фазовая скорость выбранной моды нормальной волны;
C_R - скорость поверхностной волны.With known wall thickness, ultrasonic testing frequency and their propagation velocity in the acoustic transducer waveguide and wall material, the input angles α and β are determined from the relations

Where
C ₁ is the speed of sound in the waveguide of the acoustic emitter;
C _f - phase velocity of the selected mode of the normal wave;
C _R - surface wave velocity.

 Inside the wall and on its surface, the normal and surface waves travel a certain predetermined distance L in the direction of the acoustic receiver and enter its input. The ultrasonic testing receiver is performed similarly to the emitter and is installed in the level control zone on a line parallel to the surface plane of the controlled liquid medium.

The speed of the normal C _f and surface C _R waves and their path from the emitter to the receiver are different, therefore, within the same period of the exciting pulses, the amplitude of each of the waves is distinguished, since their temporal position relative to the excitation pulse is different.

 Information on the presence or absence of a liquid medium at a controlled level is distinguished by the amplitude of the normal wave of the selected mode, and by the amplitude of the surface wave, information on the influence of destabilizing factors on the amplitude of the normal wave is extracted.

 The separation is based on the different reactions of normal and surface waves to the effect of a liquid medium on the wall of the tank in the control zone.

 Damping of the inner surface of the tank wall with a liquid leads to a sharp decrease in the amplitude of the normal wave due to the transition of part of the ultrasonic ultrasonic energy into the liquid, while the amplitude of the surface wave does not change. It was experimentally established that the amplitudes of normal and surface waves change proportionally with a change in the acoustic resistance of the contact layer.

 The proposed method uses the properties of a surface wave to eliminate the influence of acoustic contact on the reliability and accuracy of level control. For this, weakening of the input signal is introduced, in which the amplitude of the surface wave corresponding to the normal acoustic contact of the transducers with the wall is isolated, it is converted into a constant direction and stored. Then, when the acoustic resistance of the contact layer is changed, the changed amplitude is converted into a constant voltage, which is compared with the initial one, and depending on the difference of these voltages, the attenuation of the input signal is proportionally reduced and the amplitude of the information normal wave is increased.

 A device for monitoring the physical parameters of liquid media, in particular, the level in closed tanks, containing two identical inclined acoustic transducers mounted on the outer surface of the tank at a fixed distance towards each other, serially connected exciter and power amplifier connected to one of the acoustic transducers, series-connected amplifier, selector stage (first input), detector and measuring stage, series-connected sync a resonator, a delay unit, a driver of a strobe pulse, connected - a synchronizer to the input of the pathogen, and a driver of a strobe to the second input of the first selector stage, connected between the amplifier and the detector [2].

 The disadvantage of this device is the low reliability and accuracy due to the dependence of information signals on the influence of destabilizing factors, for example, the changing acoustic resistance of the contact layer between the acoustic sensors and the tank wall.

 The purpose of the proposed device is to increase the reliability and accuracy of level control of liquid media in closed tanks when changing the acoustic contact of the ultrasonic sensors with the wall.

 This goal is achieved by the fact that the device further comprises a second delay block connected in series, a second strobe driver, a second selector stage (first input), a second peak detector, a comparator (first input), a match circuit (first input), a counter, a decoder, an analog block keys, the output of which is connected to the second input of the attenuator, the input of the second delay unit and the second input of the matching circuit connected to the output of the synchronizer; connected in series to a second acoustic transducer, a summing device, an attenuator (first input), an amplifier, the output of which is connected to the second input of the second selector stage; a reference voltage source connected to the second input of the comparator.

 Functional diagram of the device and pulse potential diagrams explaining its operation are shown in FIG. 12.

 The device contains a serially connected synchronizer 1, a driver 2 and a power amplifier 3, connected by an output to an acoustic emitter 6, consisting of piezoelectric transducers 4, 5 mounted on a waveguide 7 at angles α and β; an acoustic receiver 8, consisting of piezoelectric transducers 10, 11 mounted on the waveguide 9 at angles α and β, connected to an output to the input of a serial circuit consisting of an adder 12, an attenuator 13, an amplifier 14, and an output connected to the second inputs of the selector stages 15, 16 , a serial circuit consisting of a delay unit 20, a shaper 18, a selector stage 16, a peak detector 22 and a measuring stage 23, the input of this circuit is connected to the output of the synchronizer 1; a serial circuit consisting of a delay unit 19, a shaper 17, a selector stage 15, a peak detector 21, a comparator 24, the second input of which is connected to a reference voltage source 25, coincidence circuit 26, the second input of which is connected to synchronizer 1, counter 27, decoder 28 , the block of analog keys 29, the input of this circuit is also connected to the synchronizer 1, the output of the block 29 is connected to the attenuator 13, the wall 30 of the tank, on which the acoustic emitter 6 and receiver 8 are installed.

 The operation of the device is as follows.

 A pulse generator consisting of a synchronizer 1, a driver 2 and a power amplifier 3 generates a sequence of pulses (1e), which are fed to the piezoelectric transducers 4, 5 of the emitter 6. The transducers 4, 5 excite in the waveguide 7 elastic longitudinal ultrasonic testing, which are introduced at angles α and β into the tank wall.

At the entry point on the outer surface of the wall, the longitudinal ultrasonic waves are refracted and form a surface wave 31 and a normal wave of the necessary mode 32. Inside the wall and on the surface, two waves travel a certain predetermined distance L, at which the acoustic receiver 8 is installed. At the wall-waveguide 9 surface and normal waves are transformed into longitudinal ultrasonic testing, which excite piezoelectric transducers 10, 11 mounted on the waveguide 9 at the same angles α and β.
The output electrical signals of the converters 10, 11, equivalent to the amplitudes of the surface and normal waves, are summed in an adder 12. The output signal (12g) of the adder is sent to a multi-stage attenuator 13, in which all attenuation stages are introduced. The number of signal attenuation steps (12g) is determined by the permissible range of variation of the amplitude of the normal wave 32 and the accuracy with which it is adjusted. The minimum allowable signal at the attenuator output with fully attenuated attenuation should exceed the sensitivity threshold of the amplifier 14 connected to the attenuator 13 output. Using the selector stages 15, 16, the amplitude of the normal (16l) and surface (15k) waves is extracted using the selector stages. To do this, according to the signals (1e) of the synchronizer 1, delay units 19, 20 form pulses whose duration corresponds to the propagation time (τ ₁ and τ ₂ ) of the amplitude of the normal and surface waves.

 On the trailing edge of the pulses, the shapers 17, 18 generate strobe pulses (17z and 18i) that control the operation of the selector stages 15, 16.

Peak detectors 21, 22 convert the amplitudes of the surface and normal waves into proportional constant voltages. The voltage (21 m) of the peak detector 22 controls the operation of the measuring stage 23, which has its own threshold U _c .

When damping the inner surface of the wall with a liquid in the control zone, a constant voltage (22n) at the output of the peak detector, proportional to the amplitude of the normal wave (12b), decreases relative to the response threshold U _{c of the} measuring stage 23, signaling the presence of liquid at the control level.

The constant voltage of the peak detector 21 is supplied to the input of the comparator 24, at the second input of which the amplitude of the surface wave (12a) is set using the reference voltage source 25 as the reference voltage level (21m) corresponding to the normal acoustic contact of the transducers with the tank wall. When changing the acoustic contact (increasing the resistance of the contact layer), the voltage (21 m) at the output of the peak detector 21 decreases relative to the reference U _op by ΔU, switching the comparator 21, which is installed at the input of the matching circuit 26, the resolving potential (24 °).

 The pulses of the synchronizer (1e) sequentially through the coincidence circuit 26 pass to the input of the counter 27 and switch it. The decoder 28 converts the state of the counter into a sequence of potentials (28c) at its outputs, which are connected to the block of analog keys 29. The analog keys sequentially by signals (28c) turn off the attenuation stages of the attenuator 13, thereby restoring the amplitude of the normal wave 32.

 The proposed invention is new, because it is not known from the prior art relating to the determination of the level of liquid media in closed tanks and uses an unknown method of ultrasonic monitoring of the physical parameters of liquid media, in particular, the level in closed tanks, namely, that in the zone of control into the tank wall at a certain angle to it parallel to the surface of the medium being monitored using an acoustic emitter periodically introduce an ultrasonic wave, the track speed th along the input surface is set equal to the speed of the normal wave of the selected mode propagating on a fixed part of the wall, this wave is taken by an acoustic receiver and its amplitude is used as an information signal about the level, characterized in that at the same time they additionally excite a surface wave that is insensitive to damping of the tank wall by , receive it with the same acoustic receiver, attenuate the received input signal containing both waves, emit the surface wave, detect it and form a threshold signal whose value is stored, compare the amplitude of the surface wave with the threshold signal and when it decreases, form a periodic sequence of control pulses, the number of which is proportional to the decrease in the amplitude of the surface wave relative to the threshold signal and inversely proportional to the value of the initially introduced attenuation, direct control pulses in the attenuation circuit of the input signal and restore the amplitude of the information normal Wave.

 The proposed device, which contains a serially connected synchronizer 1, a driver 2 and a power amplifier 3, connected to the output of an acoustic emitter 6, consisting of converters 4, 5 mounted on the waveguide 7 at angles α and β; an acoustic receiver 8, consisting of transducers 10, 11 mounted on the waveguide 9 at angles α and β and connected to an output to the input of a serial circuit consisting of an adder 12, an attenuator 13, an amplifier 14, and an output connected to the second inputs of the selector stages 15, 16 ; a serial circuit consisting of a delay unit 20, a shaper 18, a selector stage 16, a peak detector 22 and a measuring stage 23, the input connected to the output of the synchronizer 1; a serial circuit consisting of a delay unit 19, a shaper 17, a selector stage 15, a peak detector 21, a comparator 24, the second input of which is connected to a reference voltage source 25, coincidence circuit 26, the second input of which is connected to synchronizer 1, counter 27, decoder 28 , block of analog keys 29, the input connected to the synchronizer 1, and the output to the attenuator 13; the wall 30 of the tank, on which the acoustic emitter 6 and the receiver 8 are installed.

 The proposed inventions have an inventive step, since they use an unknown method and device that increase the reliability and accuracy of controlling the level of liquid media in closed tanks by compensating for the influence of the acoustic resistance of the contact layer on the amplitude of the information normal wave.

 The proposed inventions are applicable in industry to control the level of liquid media in high-pressure tanks of hydraulic presses, tanks with liquid chlorine and ammonia, industrial vessels and oil separators of computer refrigeration units, tanks with concentrated acids, etc.

Bibliography
1. US patent 4145917, 73/53, 1979.

 2. Copyright certificate of the USSR N 599203 G 01 F 23/28, 1978.

 3. USSR author's certificate N 343155, G 01 F 23/28, 1972.

Claims (2)

 1. The method of ultrasonic level control in tanks, which consists in the fact that a longitudinal ultrasonic wave is periodically introduced into the wall of the tank at a certain angle to it using an acoustic emitter so that a normal wave forms in the tank wall as a result of refraction the selected mode, propagating on a fixed section of the wall, take this wave with an acoustic receiver and use its amplitude as an information signal about the level, and the illuminator and the receiver are arranged along a line parallel to the surface of the liquid under control, characterized in that they simultaneously additionally excite a surface wave that is insensitive to damping of the tank wall by the liquid in the level control zone, receive it with the same acoustic receiver, attenuate the received input signal containing both waves, isolate in it the amplitude of the surface wave, detect it and form a threshold signal, the value of which is stored, when the acoustic resistance of the contact of the layer, the changed amplitude of the surface wave is compared with a threshold signal, and when it is reduced, a periodic sequence of control pulses is generated, the number of which is proportional to the decrease in the amplitude of the surface wave and inversely proportional to the value of the initial attenuation, control pulses are sent to the attenuation circuit of the input signal and the amplitude of the information signal is restored.  2. A device for level control in tanks containing an acoustic emitter and an acoustic receiver mounted on the outer surface of the tank in a line parallel to the surface of the liquid being monitored at a fixed distance towards each other, a generator, an amplifier and a first peak detector connected to the measuring stage, while the acoustic the emitter and acoustic receiver contains the first piezoelectric transducers mounted on waveguides at an angle α to the tank wall, characterized in that the generator p consists of a series-connected synchronizer, exciter and power amplifier connected to an acoustic emitter, the amplifier is connected in series with the first input of the first selector stage and the first peak detector, the synchronizer is connected in series with the first peak delay unit, the first strobe driver, the second input of the first selector stage, the second delay unit is connected in series with the second driver of the strobe pulse, the first input of the second selector stage, the second a peak detector, the first input of the comparator, the first input of the matching circuit, a counter, a decoder, an analog key block, the output of which is connected to the second input of the attenuator, the input of the second delay unit and the second input of the matching circuit are connected to the output of the synchronizer, the acoustic receiver is connected in series with the summing device, the first input of the attenuator and the amplifier, the output of which is connected to the second input of the second selector stage, the second input of the comparator is connected to a reference voltage source, and the bushy emitter and receiver contain second piezoelectric transducers mounted on the waveguides at an angle β to the tank wall.

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