SU170695A1 - DEVICE FOR MEASUREMENT OF THICKNESSES! - Google Patents

Description

Instruments are known for measuring the thickness of thin non-magnetic and non-metallic coatings on a ferromagnetic base, for example, eddy-current devices such as "Dermitron.

The proposed device is based on the magnetoharmonic method. In it, in order to eliminate the influence of changes in magnetic permeability and ferromagnetic base thickness on measurement accuracy, a measuring bridge with inductive sensors and balancing elements is connected to the inputs of a two-channel resonant amplifier, the first channel of which is tuned to the third frequency harmonic and the second frequency of the generator.

FIG. 1 shows a block diagram of the device; in fig. 2 - his electrical circuit.

The device contains a measuring bridge /, a compensation bridge 2, a sinusoidal voltage generator 3, a buffer stage 4, a resonant amplifier 5, a detector 6, a lamp voltmeter 7, a differential stage S, a selective amplifier 9, a detector 10, a summing unit 11 and a block food 12.

The measuring bridge / using a resonant amplifier S, detector 6 and lamp voltmeter 7 is balanced in the absence of the product under the sensor for the third harmonic of the frequency of the power supply of the bridge. At the same time, it remains unbalanced in terms of the main frequency. From the output of the Bridge / unbalance signal, a postPisg to the input of the differential stage 5, is amplified by a selective amplifier 9, detected by the detector 10 and measured by a lamp voltmeter 7.

To compensate for the unbalance of the measuring bridge / at the main frequency, a compensation bridge 2 serves, the voltage from which also goes to the differential cascade 8. Thus, the measuring bridge / is balanced by blocks 5, 6 and 7 for the third harmonic, and with the power of blocks 2, 8. 9, 10 -7 7 - the main frequency. When one of the sensors of the working bridge is placed on the product, the bridge will become unbalanced both in the fundamental frequency and in the third harmonic. The unbalance signals of the measuring bridge with respect to the fundamental frequency and the third harmonic, after amplification by resonant amplifiers 9, 5 and detected by detectors 10 and 6, enter the summing unit //.

The sum signal is measured by a DC voltmeter. The gain control of blocks 5 and I achieve a detuning from the effect of a change in the magnetic permeability of the ferrite IOD. LOGO on the readings of the instrument.

A push-pull generator 13 with capacitive feedback generates a sinusoidal voltage with a given frequency; These oscillations, through an isolating capacitor, arrive at the control grid of the buffer buffer stage M whose anode load is a transformer 15, the secondary windings of which feed a compensation bridge 16 and a measuring bridge consisting of two overlapping inductive sensors 17 and balancing elements 18. From the output of the measuring bridge, the voltage unbalance is fed to the input of a two-channel resonant amplifier having two channels, the first of which, assembled on two lamps 19, is tuned to the third harmonic, and the second, assembled on lamps 20, is tuned to the main frequency of the generator. At the output of both channels, the amplified unbalance voltage of the measuring bridge is detected by diodes 21 and 22.

A differential lamp voltmeter 23 using a switch 24 alternately measures the DC component of the detection voltages directly on

output of each channel, as well as on the summing cell 25.

Subject invention

A device for measuring the thickness of thin non-magnetic and non-metallic coatings on a ferromagnetic base, comprising a generator, a measuring and compensating bridges, a resonant amplifier, a differential cascade, two detectors, a summing unit and a measuring device, characterized in that, in order to eliminate the effect of a change in the magnetic permeability of the base on measurement accuracy, a measuring bridge with inductive sensors and balancing elements is connected to the inputs of a two-channel resonant amplifier, the first channel of which is us Roen at the third harmonic frequency, the second - on the main oscillator frequency.