SU368471A1 - LIBRARY 1 - Google Patents

Description

A vortex current device for measuring the distance to a metal surface contains an eddy current sensor, an oscillator that includes a sensor, a reference oscillator, a frequency converter connected to the output of the oscillator and a reference oscillator, and a frequency detector connected to the output of the frequency converter.

The proposed device differs from the known one in that it is additionally equipped with a phase-shifting chain included in the oscillator circuit, and the frequency detector is designed as a series-connected valve and two triggers and connected to the trigger input of the multivibrator. This increases the accuracy and reliability of the measurement.

FIG. 1 shows a block diagram of the proposed device; in fig. 2 is a block diagram of an auto generator; in fig. 3 is a block diagram of a frequency detector; in fig. 4 - amplitude-frequency characteristics of the oscillator circuit of the oscillator; in fig. 5 - phase-frequency characteristics of the oscillator circuit of the oscillator.

The device contains a sensor / included in the oscillating circuit of the auto-oscillator 2, the reference oscillator 3, the frequency converter 4, the inputs of which are connected to the outputs of the auto-generator and the reference oscillator, and the output to the input of the low-pass filter 5. The device also contains an amplifier-limiter 6 connected in series with the filter 5, a frequency detector 7 and a low-pass filter 8.

The device's oscillator is made up of amplifiers 9 and 10, an oscillatory circuit 11, and a phase-shifting chain 12 connected between amplifiers 9 and 10.

Frequency detector 7 contains a multivibrator 13 connected by an output to the first input of the trigger 14, which is connected by an output through a valve 15 to a common input of the trigger 16, the output of which is connected to the second input of the trigger 14. The second input of the valve 15 is connected to the output of the amplifier-limiter 6.

Curves I (figs. 4 and 5) correspond to the smallest introduced inductive resistance and the greatest introduced active

0 resistance; curves П correspond to the greatest introduced inductive resistance and the smallest introduced active resistance.

At some frequency fr, the phase-frequency characteristics intersect, and the phase shifts are equal to each other.

The device works as follows.

One of the conditions for generation is that the phase shift in the closed 0 circuit is zero: amplifier input — amplifier output —

oscillatory circuit - amplifier input. Therefore, the phase-shifting chain is chosen such that the phase shift in the circuit: amplifier

9-phase-shifting chain 12 - amplifier

10 was equal in the whole range of measured displacements. In this case, in order to ensure that the total phase shift in the closed circuit of the oscillator is equal to zero, a phase shift occurs in the oscillatory circuit. For a given distance between the sensor and the surface, the generation frequency will be equal to / g and the same for surfaces with extreme electromagnetic properties and close to fz for surfaces with intermediate electromagnetic properties. When the distance between the eddy current sensor and the surface under study changes, the magnitude of the inductive and active resistance introduced into the coil of the Bi-Bi-heating sensor changes. As a result, the frequency of the oscillator changes. After conversion in the frequency converter and filtering by a low-pass filter, the voltage, whose frequency is equal to the difference between the frequencies of the auto-oscillator and the reference oscillator, goes to the amplifier-limiter 6 and then to the frequency detector 7.

The impulse of the multivibrator 13 transfers the trigger 14, the voltage at the output of which opens the valve 15. Two pulses of intermediate frequency, the passage through the valve 15, form an impulse at the output of the trigger 16.

the duration of which is equal to the period of the intermediate frequency. The falling edge of this pulse transfers trigger 14 to its original state. When the frequency of the multivibrator is coaxial, the constant voltage component at the output of the trigger 16 is inversely proportional to the intermediate frequency. If the frequency of the reference oscillator is chosen so that the intermediate frequency is back

proportional to the distance, then the constant component of the voltage at the output of the device will linearly depend on the distance between the sensor and the surface.

Subject invention

An eddy current device for measuring the distance to a metal surface, containing an eddy current sensor, an autogenerator with a sensor included, a reference oscillator, a frequency converter connected to the outputs of the autogenerator and a reference oscillator, and a frequency detector connected to the output of the frequency converter, the fact that, in order to increase the measurement accuracy, it is additionally equipped with a phase-shifting chain included in the oscillator circuit, and the frequency detector is made in the form of connected valve and two triggers and connected to the trigger input of the multivibrator.

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