SU605081A1 - Method and apparatus for monitoring sheet material thickness - Google Patents

Description

one

This invention relates to non-destructive quality control of materials and may be used in metal processing plants.

There is a method according to which a double-sided echo-location of the material is performed, which involves comparing the propagation time of the echoes with a reference echo-signal 1. The disadvantage of this method (which includes temperature depths) is low sensitivity in the thickness range of film materials due to the extremely small propagation time echo signals.

The closest to the proposed method to the technical essence and the achieved effect is the method of controlling the thickness of the tape material, which means that by an electrically excited electroacoustic transducer in the air in the zone adjacent to the material being monitored, they emit material oscillations in the air in another zone adjacent to the material, and according to their amplitude, the controlled parameter {2.

The disadvantage of this method is the occurrence of errors arising from changes in air temperature.

The method of controlling the thickness of the tape material is carried out using a device containing radiating and receiving electroacoustic transducers installed on the sides of the monitored tape material, excitation pulse generator connected to the output with the radiating converter, and electronic measuring unit, inputs connected to the receiver and an additional output of the generator.

The purpose of the invention is to improve the measurement accuracy.

This goal is achieved by registering temperature changes in one of the zones, forming an additional signal proportional to these changes, and adjusting the intensity of the excitation according to the ratio with its help;

 dl4 d2

 I dt g dt

where N is the additional signal of the relative intensity control;

dl

 first intensity derivative

dt

excitation of radiation from temperature t; Z is the acoustic impedance of air.

This method of controlling the thickness of the tape material can be carried out by a device containing radiating and receiving electroacoustic transducers, a generator of excitation pulses connected to it and to a receiving transducer matching transformer, electronic measuring unit, inputs connected to the receiving transducer and an additional output of the generator, and installed in the housing thermistor transducer connected between its potential plate and the output winding according its transformer, while the ratio between the value of Rt of the thermistor and the value of Ri of the electrical resistance of the radiating converter is chosen as close as possible to

-I

2 (city: K, SCH-2 dt) J

dRt

- first derivative of the thermistor dt value from the temperature /;

dz dt

-first derivative of the acoustic impedance g of air temperature.

A device for carrying out the method is shown in Fig.

It contains a radiating electroacoustic transducer 1 and receiving electroacoustic transducer 2, installed on the sides of the controlled tape material 3, a generator 4 excitation pulses connected to the output with electroacoustic converter 1, and an electronic measuring unit 5, the input connected to the electroacoustic converter 2 and an additional output of generator 4 exciting pulses.

In addition to the piezoelectric element 6, entering and receiving electroacoustic converter 2, the radiating electroacoustic transducer 1 includes a matching transformer 7, the input winding 8 of which is connected to the potential element of the piezoelectric element 6 through a coaxial cable 9 to the generator 4.

The electronic measuring unit 5 consists of a serially connected amplifier 12, a selector amplifier 13 and a measuring registering unit 14, as well as a generator 15 "strobe pulses, input connected to generator 4, and output to controlled input of selector amplifier 13.

The device works as follows.

The generator 4 produces electric pulses of stabilized amplitude, which are fed via cable 9 to radiating transducer 1 to the input winding 8 of a matching transformer 7. From the output winding 10 of the transformer, pulses are fed through a thermistor 11 to a piezoelectric element.

6. Excited by the pulses arriving at it, piezoelectric element 6 emits pulses of acoustic oscillations into the air towards the controlled material.

Due to the fact that impulses arrive at a bad element 6 through a thermistor 11, which has a negative value of the temperature coefficient of resistance, with increasing temperature, the voltage of the pulses on the plates of piezoelectric element 6 increases, blocking the change in pressure caused by the change in air impedance.

However, the simple mutual compensation of pressure changes caused by

impedance, ineffective. This is due to the fact that when impedance decreases, the acoustic transparency of the material being monitored decreases proportionally, therefore, to increase the amplitude stabilization

the acoustic impulses transmitted through the metal, the ratio of the electrical resistances of the radiating transducer and the thermistor is chosen as close as possible to

  / M

  dt - dt) j

so that the pressure of the acoustic parcel grows in proportion to the temperature change and thus the condition

J dl4 dz

I

dt

dt

The pulsed signals of the receiving electroacoustic transducer 2 through amplifier 12 are fed to a selector amplifier 13, to another input of which gates are received from a generator 15 controlled by pulses of an excitation generator 4. In amplifier 13, informative pulses of converter 2 are separated from acoustic noise and fed to measuring-recording -. The unit 14, the scale of which is calibrated in units of the thickness of the controlled material.

Claims (2)

1. The method of controlling the thickness of the tape material, which means that by means of an electrically electrically operated electroacoustic transducer in the air in the zone adjacent to the material being monitored, ultrasonic vibrations are emitted towards the material, they receive vibrations transmitted through the material in the air in another zone adjacent to , and by their amplitude, a controlled parameter is judged, characterized in that, in order to increase the control accuracy, temperature changes in one of the zones are recorded, Coziness, an additional signal proportional to these changes, n regulates with its help the intensity of the excitation of the radiation according to the relation: 1 dl4 ds L / dt g dt where L is the additional signal of the relative intensity control; dl first intensity derivative dt excitation of radiation from temperature i; Z-acoustic air impedance. 2. A device for carrying out the method according to claim 1, comprising radiating and receiving electroacoustic transducers installed on the sides of the controlled tape material, excitation pulse generator, matching transformer connected to the generator output and receiving electroacoustic driver, electronic measuring unit, connected to the receiving electro-acoustic transducer and an additional output of the generator, a thermistor mounted in the case of the radiating electroacus nical connected between the converter and its potential electrode and the output winding of the matching transformer, wherein otnoschenie value Ri between the thermistor and the value of /, the electrical resistance of the radiating transducer selected possibly close to the value: rf dt dz Rt Ttj dRt Where - first derivative of dt thermistor for temperature t, dz dt - first derivative of acoustic impedance Z air temperature t. Sources of information taken into account in the examination 1. USSR author's certificate No. 393667, cl. G 01N 29/00, 1971. 2. Authors collection of the USSR No. 266404, cl. G 17/02, 1968.