SU1486909A1 - Method and apparatus for automatic testing of pulp hard inclusion main characteristics - Google Patents

Description

The invention relates to the technique of acoustic measurements and can be used to automatically control the main characteristics of solid pulp inclusions, in particular the concentration of the solid phase and the particle size distribution of the crushed material in the pulp.

The purpose of the invention is to improve the accuracy of control by reducing measurement errors by measuring characteristics that are independent of the parameters of gas bubbles.

The drawing shows a block diagram of a device for the automatic control of the main characteristics of solid pulp inclusions.

In the drawing, the first 1 and second 2 measurement channels are indicated, a 20 tor 3 generator, an emitting transducer 4, a receiving transducer 5, a preamplifier 6, a selection unit 7, a logarithmic amplifier 8 $ delay circuit 9, a subtraction unit 10, 25 division unit 11 , multivibrator 12, measuring chamber 13, one-shot 14, one-shot 15 delay, differentiator 16, amplitude stop 17 and forming a single-oscillator 18.

The method of automatic control of the main characteristics of solids pulp is as follows. -zs

one' . .

In the pulp flow passing through the measuring chamber, emit ultrasonic vibrations and exercise. reception passed through the flow of vibrations. At the same time, the Lamb waves are excited in the wall of the measuring chamber and are received at a fixed distance from the excitation point. “Then, the amplitudes of the received oscillations are measured: A _o - ultrasonic waves passing through the stream;

And _l - Lamb waves propagating in the wall of the measuring chamber. The concentration of solid inclusions is determined by the amplitude of A _l , and the content of the size class is determined from the expression

P ^ = (1n A _o - 1n A _L ) / 1n A _l

and control the content of $$

class size.

A device for automatic control of the main characteristics of solid pulp inclusions contains two channels I and 2 measurements, a multivibrator 12, · two single vibrators 14, the inputs of which are connected to the output of multivibrator 12, and the output of each of them - to the input of one of the channels 1 and 2. Device takhke contains a block

10 subtraction, the inputs of which are connected to the outputs of channels 1 and 2, block

11 divisions, the first input of which is coeno dinene with the output of subtraction unit 10,

and the second - with the output of the second channel 2, and the measuring chamber 13. Each of the channels 1 and 2 consists of a series-connected generator 3 and a radiating transducer 4, a receiving transducer 5, a pre-amplifier 6, a selection unit 7 and a log-amplifier 8.

Each of channels 1 and 2 also includes a delay circuit 9, the input of which is connected to the output of the multivibrator 12, and the output - to the input of the selection unit 7. Each delay circuit 9 is made in the form of a delayed one-shot 15, a differentiator 16, an amplitude limiter 17 and a forming one-shot 18. 4 and 5 channels 1 and 2. Transducers 4 and 5 of the first channel 1 are mounted on the walls of the measuring chamber 13 so that during the monitoring a controlled flow of pulp is heard Removable 'ultrasonic waves, and the transducers 4 and 5, the second channel 2 are in the form of Lamb waves and transducers are installed on the walls of the measuring chamber 13 so that control is performed during radiation and receiving Lamb waves.

Device for automatic control of the main characteristics of solids pulp works as follows.

Through the measuring chamber a stream of pulp is passed to be monitored. Multivibrator 12 generates square-wave pulses, each of which, by means of triggering single-shot oscillators 14, starts the generators of 3 channels 1 and 2, which in turn form video pulses of a given frequency. · Turn-on time ge5

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Nerators 3 and, therefore, the duration of the video pulses is determined by the duration of the pulses generated by the triggering one-shot 14, Emitting transducers 4, such as piezoceramic type, convert electrical oscillations into elastic ultrasonic vibrations. The transducer 4 of the first channel 1 excites through the walls of the measuring chamber 13 in the pulp flow longitudinal ultrasonic vibrations. During the propagation of ultrasound in the pulp, it is absorbed and scattered, and the scattering of ultrasound significantly exceeds the absorption when the size of particles with a wavelength is comparable (for particles of 50–100 µm in size, this condition corresponds to a frequency of 5–10 MHz). The absorption and scattering of sound is also affected by the presence of gas bubbles in the pulp. The process of ultrasound attenuation on gas bubbles has a pronounced resonant nature and at frequencies of the order of 5 MHz, the ultrasound on gas bubbles practically does not attenuate, since this frequency corresponds to the size of the bubbles at which they dissolve in water. Thus, the degree of attenuation of high-frequency ultrasonic oscillations as they pass through the pulp stream is determined only by the size of the solid phase particles and their concentration. The Converter 4 of the second channel 2 excites in the wall of the measuring chamber 13 of the Lamb wave.

The attenuation of the Lamb wave propagating in the wall of the measuring chamber 13, which is in contact with one side with a controlled volume of pulp, is determined only by the concentration of the crushed material in the pulp and does not depend on the size of the particles of the solid phase and the presence of gas bubbles (due to their small mass). Ultrasonic oscillations propagating in the pulp and in the wall of the measuring chamber 13 reach receiving transducers 5 located at a fixed distance from the corresponding radiating transducers 4. Transducers 5 convert acoustic oscillations into electrical signals amplified by preamplifiers 6 and fed to

blocks 7 selection. In the latter, a temporary selection of the received signals is made using control

_{from the} signals from the outputs of the circuits

9 delays, in order to reduce the effect of noise and eliminate the possible interaction of Lamb waves and longitudinal waves excited in a single measuring

10 camera 13.

The control signals in delay circuits 9 are generated as follows. Pulse from the multivibrator 12 triggers one-shot delays 15, which generate pulses whose duration is determined by the time required for propagation from the radiating transducers 4 to the receiving transducers 5 of the corresponding ultrasonic vibrations (longitudinal waves for the first channel 1 and Lamb waves for the second channel 2) „ Formed by one-shot 15 positive rectangular, pulses after differentiation by differentiators 16 are converted into two (positive and negative) short after successive pulse. The amplitude limiters 17 transmit only the second of them (negative), which triggers the forming one-shot 18. The latter generate pulses arriving at the output of circuit 9 for 35 holders. In blocks 7, electrical signals are transmitted from the preamplifiers 6 to the logarithmic amplifiers 8 only at the moment of the existence of a control pulse 40 formed by the delay circuit 9. Logarithmic amplifiers 8 produce the final amplification of the received oscillations and the calculation of the logarithm of the input signals. The amplitude 45 of the output signal of the second channel 2, measured with the help of the amplifier 8, is proportional to the concentration of β, solid inclusions and serves to control this parameter.

10 subtraction where subtracted logarithm of the amplitude A _n, the received second channel signal 2 from lo • logarithms of the amplitude A _{of the} signal prinya55 of the first channel 1 from the output unit 10 subtracting the signals received at the first input of the division unit 11, and, its second input receives signals from the output of the second channel. 2. In block 11

Ί

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the signal received at the first input is divided by the signal received at the second input. The amplitude of the output unit 11, iz ₅ Merenii with its help, proportional to the size class and is used to monitor the parameter of

Thus, a device for the av-10 tomato control of the main characteristics of solid pulp inclusions measures the concentration of the solid phase and the content of the grain size of interest in the pulp flow, regardless of the parameters of the gas phase and without prior degassing of the controlled medium with high accuracy.

Claims (1)

1. A method of automatic control of the main characteristics of solid pulp inclusions, consisting in the fact that they emit ultrasonic vibrations into the pulp flow passing through the measuring chamber, receive oscillations passing through the flow, measure the amplitude A _{o of the} received oscillations and, taking into account its magnitude, determine the monitored parameters, characterized in that, in order to increase accuracy, the Lamb waves are additionally excited in the wall of the measuring chamber, take them at a fixed distance and measure their amplitude A _l , the concentration of solid inclusions is determined by the amplitude A _L , and the content (3 ^ size class is determined from the expression P ' _£ ) ^{= (1p A} o " ^{1p A} l) / ^{1p A} m 2. Device for automatic control of the main characteristics of solid pulp inclusions, containing two measurement channels, each of which consists of a series-connected generator and a radiating transducer, a receiving transducer, a pre-amplifier, a selection unit and a logarithmic amplifier and a delay circuit, the output of which is connected to the second input of the selection unit, subtraction unit The inputs of which are connected to the outputs of the channels, a division unit, a multivibrator and a measuring chamber for passing the pulp, on the walls of which the device Converters are installed, characterized in that, in order to improve accuracy, it is equipped with two triggering single-oscillators, the inputs of which are connected to the output of the multivibrator, and outputs to the input of each channel, each delay circuit is made in the form of serially connected delay single-oscillator, differentiator, amplitude limiter and forming one-shot, the input of the delay circuit is connected to the output of the multivibrator, the inputs of the division unit are connected to the output of the second measurement channel and the output of the subtraction unit, and The spruces of the second channel are made in the form of Lamb wave transducers. 1486909 A1 3 1486909 four