SU1252657A2 - Eddy-current thickness gauge of dielectric coatings - Google Patents

Abstract

The invention makes it possible to reduce the error in thickness measurements due to the influence of external destabilizing factors. For this purpose, the measuring path of the thickness gauge, containing successively connected harmonic oscillator, eddy current transducer (VTP), amplifier, amplitude detector, logarithmic amplifier, an amplifier and amplitude detector are introduced that are completely identical to the main one. At the input of the amplifier with the removal from the part of the turns of the VTP coil, the gain is directly proportional to the value of the exciting current of the VTP. This voltage, after amplification and detection, affects the input of a controllable source of the reference current of a logarithmic amplifier. A change in the transmission coefficient of the latter is opposite to a change in the exciting current and reduces the multiplicative measurement error associated with its fluctuations. Due to the identical parameters of the amplifiers and amplitude detectors, the measurement error is reduced due to the temporal and temperature drift of the transmission coefficients of these units. 1 il. (L SP to OD SL

Description

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The invention relates to non-destructive quality control of the components by the method of vortex currents, can be used to measure the thickness of dielectric coatings deposited on electropneumatic non-magnetic bases, and is an improvement of the known eddy current thickness gauge according to ed. sn. No. I153233.

The purpose of the first invention is to increase the accuracy of measurements by reducing the instrumental error.

The drawing shows a block diagram of the device.

The device contains a series-connected harmonic current generator I, an overhead eddy current transducer 2 (VTP), a main channel consisting of a series-connected amplifier 3 and an amplitude detector 4, a logarithmic amplifier 5, a multiplier 6 and an indicator 7, an additional channel identical in parameters to the main and consisting of a series-connected amplifier 8 and an amplitude detector 9, including between the part of the turns from a portion of the ECP useful coil and the input of a controlled source of reference current 10 ogarifmicheskogo amplifier series connected source 10 and reference voltage adder and a second input connected to the output of the logarithmic amplifier 5, and an output coupled to a second input of multiplier 6.

The device works as follows.

Generator 1 feeds a sinusoidal current of fixed amplitude and frequency ECP. As a result of the electromagnetic interaction of the VTP with the control object, a signal is produced at the output of the measuring coil of the converter and which is equal to

U, Igf (n), (I) where IB is the ETP excitation current;

f (n) is the known function of the measured thickness: h of the dielectric layer.

The signal Uj, passing through the main channel with the resulting transmission coefficient K, is fed to the first input of the logarithmic amplifier 5. It is made according to a thermally compensated circuit with a reference current controlled by HtTO4HHKOM, which is matched in terms of the parameters of a pair of transistors, foriating 526572

The logarithmic function of the amplifier is 5. The input of the controlled reference current source, i.e. second (t input logarithmic amplification, 5 liters, dongle) to the output of the additional channel thickness gauge. The input voltage of the additional channel is removed from the outlet from a portion of the turns of the VTP 2 useful coil. It is possible to perform this removal, for example, from a resistor connected to the current winding circuit. It is proportional to the magnitude of the excitation current at the operating frequency of the converter, therefore, the second input 15 of the logarithmic amplifier is affected by the reference voltage, where K is the additional channel transmission coefficient equal to K.

According to equality (1), the conversion function of the input signal of the logarithmic amplifier is

(-U) (2)

on

where K is the transfer coefficient of the logarithmic amplifier, K is the coefficient determined by the parameters of the logarithmic circuit.

Bear in mind that V b

20

25

thirty

five

40

45

50

55

K, UC,

given the raiz equality (2) of the state () receive

and5 КзК „1п 1ЧЬ),

those. the output voltage of the logarithmic amplifier does not depend on the magnitude of the excitation current, as well as on the temperature and time fluctuations of the coefficients of the main and additional channels.

Further processing of the measured signal occurs in accordance with the conversion function, having the form

, U, (), (3), where C and C, j are constant coefficients.

Claims (1)

Invention Formula Eddy current thickness gauge dielectric coatings ed. St. No. 1153233, characterized in that, in order to improve the measurement accuracy, it is equipped with an additional channel, identical in parameters to the main one and including series-connected amplifier and amplitude detector, eddy current transducer is made with a branch from the part of the turns of the payload coil to which the additional channel input is connected, and the logarithmic amplifier is made according to Voltage reference current source, input Editor M. Blanan Compiled by V. Kuznetsov Tehred M. Khodanich Proofreader L; Pilipenko A615 / 43 Circulation 670 Subscription VNIIPI USSR State Committee for inventions and discoveries 113035, Moscow, Zh-35, Raushsk nab., 4/5 Production and printing company, Uzhgorod, st. Project, 4 telno channel.