RU2104503C1 - Method determining velocity of ultrasound - Google Patents

Abstract

FIELD: measurement technology. SUBSTANCE: method is meant for determination of ultrasound parameters and indices of liquid and gaseous media functionally dependent on velocity. Tested gas is let pass through standard and tested channels in agreement with method. Mode of autocirculation of electroacoustic pulses is set in tested channel and pulse mode of passing of electroacoustic pulses with simultaneous excitation of both channels is established in standard channel. Then train of reference electric pulses is formed from pulses of autocirculation and from pulses passed through standard channel there are formed pulses used jointly with reference pulses for formation of standard time interval equal to time of propagation of acoustic pulse in standard channel. After this test time intervals equal to time of propagation of acoustic pulse in tested channels are formed. Pulses are generated , test intervals are filled with high-frequency pulses and standard intervals are filled at same time with counting of these pulses. Then filling of standard intervals is stopped at time moment when total number of high-frequency pulses filling test intervals reaches fixed number. Number of high-frequency pulses emerged with filling of seven standard intervals from moment of start to moment of finish of filling is used to evaluate velocity of ultrasound. EFFECT: increased authenticity of method. 1 dwg

Description

 The invention relates to non-destructive testing of materials, substances and products by the speed of propagation of ultrasonic vibrations and can be used to signal fast measurements of the composition of gaseous, for example, air media.

 There is a method of determining the speed of ultrasound, in which the difference between the pulse repetition frequencies of two channels (reference and measuring) is measured, each of which forms a feedback system, then the difference frequency voltage is filtered, and then the number of difference frequency pulses is amplified, limited and counted [1] .

 The disadvantage of this method is that full compensation of the influence of atmospheric humidity on the measurement result is impossible.

 The closest to the invention in technical essence and the achieved result (prototype) is a method for determining the speed of ultrasound, which consists in the fact that in the controlled channel set the mode of auto-circulation of electro-acoustic pulses, and in the reference channel, the pulse mode of transmission of electro-acoustic pulses with simultaneous excitation of both channels, form a sequence of reference electrical pulses with a frequency of autocirculation and a sequence of electrical pulses of the same frequency The repetitions generated after the acoustic signal passes the reference signal use both of these sequences to form a reference time interval equal to the propagation time of the acoustic pulse in the reference channel, and the speed of ultrasound is judged by the total number of high-frequency pulses filling the reference intervals during the measuring time interval, high-frequency pulses are received from a stable generator, form control time intervals equal to the propagation time acoustic pulse in the controlled channel, and for the measuring time interval, take the time interval during which the total number of high-frequency pulses filling the control intervals reaches a fixed number [2].

 The disadvantage of this method in the following. When controlling air pollution by harmful gases, a controlled gas enters the measuring channel, and the reference channel is closed. The measuring channel communicates with the external environment and is filled with gas with a certain value of relative humidity φ of air, and a change in the frequency of autocirculation at different values of φ occurs along curves close in nature and multiplicative effect.

 In this case, the relative weight content of moisture vapor X remains constant in the reference channel, and the change in the autocirculation frequency in it has an additive character (curves X = 1.8%, X = 1.3%, X = 1%, X = 0; according to Fig. . 6.22, p. 192 [3]).

 As a result, full compensation of the influence of air humidity on the measurement result is not possible. The measurement error by the method of correcting the influence of atmospheric humidity [3, p. 194] even in a narrow range of changes in relative humidity from φ = 100 to φ = 60% is ± 0.12% of the nominal value of the measured value, which is two to three orders of magnitude exceeds the permissible error of the gas analyzer in the control of most harmful gases [4].

 The essence of the invention is achieved by the fact that in the controlled channel set the mode of autocirculation of electro-acoustic pulses, and in the reference channel, the pulse mode of passage of electro-acoustic pulses with simultaneous excitation of both channels, form a sequence of reference electrical pulses with a frequency of autocirculation and a sequence of electrical pulses of the same repetition frequency generated after acoustic signal passage of the reference channel, use both of these sequences the formation of the reference time interval equal to the propagation time of the acoustic pulse in the reference channel, and the speed of ultrasound is judged by the total number of high-frequency pulses filling the reference intervals during the measuring time interval. High-frequency pulses are obtained from a stable generator, control time intervals are formed equal to the propagation time of the acoustic pulse in the controlled channel, and the time interval during which the total number of high-frequency pulses filling the control intervals reaches a fixed number is taken as a measuring time interval. According to the invention, a controlled gas is passed through a reference channel.

 As a result, with a sharp (volley) discharge, for example, of ammonia into the atmosphere, its concentration in the controlled channel quickly reaches the concentration of ammonia in the air, and in the reference channel the concentration will equalize over a certain period of time, commensurate with the time that atmospheric air penetrates the reference channel.

 Thus, a gas detector with such a design will respond in a timely manner to volley emissions of substances, at the same time it will be insensitive to moisture exposure, since the measuring and reference channels communicate with the external environment and are filled with gas with a certain value of relative humidity φ of air, and the frequency change autocirculation in the channels at different values of φ occurs along curves close in nature to the multiplicative effects, which are compensated and do not affect the result of erenium.

 The drawing shows a block diagram of a device that implements the described method.

 The device contains a controlled channel of auto-circulation of electro-acoustic pulses, which is shown in the drawing by a serially connected synchronized pulse generator 1, a shaper 2 of a control interval, a radiator 3 of a vibration, a controlled medium 4, a receiver 5 of vibrations, an amplifier-forming unit 6, and also a reference channel represented in series emitter 7 of oscillations, a reference medium 8, a receiver 9 of oscillations, an intensifying-forming unit 10 and a shaper 11 of a reference interval, and the input of the emitter 7 is connected to the output of the generator 1 and the second input of the shaper 11. The device also contains a series-connected generator 12 of stable oscillations, a cascade 13 matches, a frequency divider 14, a second cascade 15 matches and a pulse counter 16, and the output of the shaper 2 is connected to the second input of the cascade 13, the output of the shaper 11 is connected to the second input of the cascade 15, the third input of which is connected to the output of the generator 12.

(контрольный интервал) и периодом T_к автоциркуляции, поступивших с выхода формирователя 2 на вход каскада 13 в течение измерительного интервала, определяется из условия:

где

- время распространения импульса в акустической среде контролируемого канала.The method is as follows. Generator 1 generates electrical impulses, which, after converting them to acoustic ones, pass through a controlled channel, go to the input of generator 1, causing a repeated autocirculation cycle of electro-acoustic pulses, and also go to the input of driver 2, are formed and go to the second input of cascade 13, controlling the passage of high-frequency pulses with a period T _o from the output of the generator 12 to the input of the divider 14 having a division coefficient K _e . The number N _to pulses with a duration

(control interval) and the period T _for autocirculation received from the output of the shaper 2 to the input of the cascade 13 during the measuring interval is determined from the condition:

Where

- pulse propagation time in the acoustic environment of the controlled channel.

, равной времени распространения импульса в акустической среде эталонного канала.The pulses from the output of the generator 1 also go to the second input of the shaper 11 and, passing through the emitter 7, the controlled medium 8, the receiver 9 and block 10, go to the first input of the shaper 11, the pulses of which are generated with a period T _for autocirculation and duration

equal to the propagation time of the pulse in the acoustic environment of the reference channel.

 From the output of the shaper 11, the pulses arrive at the second input of the cascade 15, controlling the passage of high-frequency pulses from the output of the generator 12 to the input of the counter 16.

каждый в течение измерительного интервала N_кT_к, с учетом выражения (2) равно:

Следовательно, результат измерений по описываемому способу, принимая во внимание обратную пропорциональность времени распространения акустических колебания в среде и скорость ультразвука, может быть записан в виде:

где C_к - скорость ультразвука в контролируемом канале;
C_э - скорость ультразвука в эталонном канале.The total number N _{x of} high-frequency pulses filling N _k reference time intervals of duration

each during the measuring interval N _to T _to , taking into account the expression (2) is equal to:

Therefore, the measurement result by the described method, taking into account the inverse proportionality of the propagation time of acoustic vibrations in the medium and the speed of ultrasound, can be written in the form:

where C _to - the speed of ultrasound in a controlled channel;
C _e - the speed of ultrasound in the reference channel.

справедливым и для известного способа.When choosing the conditions for the physical implementation of the method, it suffices to restrict ourselves to the ratio:

fair for the known method.

As a result of the analysis, for example, when determining the speed of ultrasound in atmospheric air, the graphs of daily changes in relative humidity of atmospheric air, the minimum time constant τ _{e of} changes in atmospheric humidity is [5] τ _e = 4000 s.
The time constant τ _{e of the} air exchange of the reference channel was chosen equal to 800 s from the condition of high-quality five-time purge of the sensor.

 In the controlled channel, the auto-circulation mode of electro-acoustic pulses is set, and in the reference channel, the pulse mode of transmission of electro-acoustic pulses is set with simultaneous excitation of both channels. Then, a sequence of reference electrical pulses is formed from auto-circulation pulses, and pulses are also formed from pulses transmitted through the reference channel and used together with the reference pulses to form a reference time interval equal to the propagation time of the acoustic pulse in the reference channel.

 Then, using autocirculation pulses, control time intervals equal to the propagation time of the acoustic pulse in the controlled channel are formed, then high-frequency pulses are received from a stable generator, the control intervals are filled with high-frequency pulses, and at the same time they begin to fill the reference intervals with high-frequency pulses, counting the number of these pulses. At the time when the total number of high-frequency pulses filling the control intervals reaches a fixed number, the filling of the standard intervals with high-frequency pulses is stopped and the ultrasound speed is judged by the number of high-frequency pulses that appeared when they filled the reference intervals from the beginning to the moment of filling completion.

 The described method allows to increase the accuracy of signaling by rapid changes in the composition of gaseous media by two to three orders of magnitude and can also be carried out in other methods and devices, the measurement result of which is proportional to the ratio of sound velocities in the measuring and reference channels.

Sources of information:
1. Nosov V. A. Design of ultrasonic measuring equipment.-M.: Mechanical Engineering, 1972, p. 109-110.

 2. SU, a.s. N 894551, cl. G 01 N 29/00, 1981.

 3.Novitsky P.V., Knorring V.G., Gutnikov V.S. Digital devices with frequency sensors.- L.: Energy, 1970, p.191-194.

 4. Vorobyov N.P. Research and development of a pseudo-selective air pollution meter for an automated control system. Dissert. for research. step. Ph.D., Tomsk, 1980, p. 43, tab. 1-7.

 5. Meteorological monthly. General Directorate of Hydrometeorological Service under the Council of Ministers of the USSR. West Siberian Hydrometeorological Service. Novosibirsk, 1973, no. 20, part 3, N 1-9.

Claims (1)

 A method for determining the speed of ultrasound, in which the mode of auto-circulation of electro-acoustic pulses is set in the controlled channel, and the pulse mode of transmission of electro-acoustic pulses in the reference channel while both channels are excited, form a sequence of reference electrical pulses with a frequency of auto-circulation and a sequence of electrical pulses of the same repetition frequency generated after acoustic signal passage of the reference channel, use both of these sequences for the formation of the reference time interval equal to the propagation time of the acoustic pulse in the reference channel, and the speed of ultrasound is judged by the total number of high-frequency pulses filling the reference intervals during the measuring time interval, high-frequency pulses are received from a stable generator, form control time intervals equal to time the propagation of an acoustic pulse in a controlled channel, and for the measuring time interval take a period of time, during which the total number of high-frequency pulses filling the control intervals reaches a fixed number, characterized in that the controlled gas is passed through the reference channel.