SU1298517A1 - Eddy-current thickness gauge of dielectric coatings - Google Patents

Description

The invention relates to instrumentation engineering and can be used to measure the thickness of dielectric coatings on a non-ferromagnetic conductor on its base.

The purpose of the invention is to increase the measurement accuracy by eliminating the temperature drift and the error associated with the instability of the oscillator,

The drawing shows a block diagram of the thickness gauge.

V sretokovy thickness gauge contains a series-connected auto-oscillator 1, eddy-current transducer (VTP) 2, amplifier 3, amplitude detector 4, logarithmic amplifier 5 and indicator 6, made in the form of an analog-digital converter, serially connected transformer 7, whose input is connected to the output of the auto-oscillator 1 , the second amplifier 8, the second amplitude detector 9, the output of which is connected to the reference input of the logarithmic amplifier 5, as well as the second logarithmic amplifier 10, the combined reference and signal the first inputs of which are connected to a source of reference voltage, and an adder 11 whose inputs are connected to the outputs of logarithmic amplifiers 5 and 10, and the output - to the reference input of the indicator 6.

Eddy current thickness gauge works as follows.

The auto-oscillator 1 feeds a sinusoidal current ETP 2, the signal from the measuring winding of which, which appears when the converter interacts with the object, is amplified by the amplifier 3 and detected by the amplitude detector 4 and logarithmized by the long-arc amplifier 5. The output signal of the logarithmic amplifier 5 is proportional to

The value is 1pA, where A is the amplitude of the voltage applied to the VTP 2. The reference voltage of the logarithmic amplifier 5 is formed by a series circuit comprising a transformer 7, an amplifier 8 and an amplitude detector 9, the output signal of which is proportional to the output voltage of the oscillator 1 and its operating frequency. The output signal of the logarithmic amplifier 5 is simultaneously supplied to the signal input of the indicator 6, and to one of the inputs of the adder 11. The output signal of the latter.

The supplied reference indicator 6 is proportional to the value V - InA + С, where C is the value directly proportional to the output (reference) signal of the logarithmic amplitude. l 10.

Indicator 6 indications are directly proportional to the input signal, i.e. 1pA, and inversely proportional to the signal supplied to the reference input of the indicator 6.

Thus, the indicator readings 6 are directly proportional to

Mk

Kdpa

one

+ Kj1пА

(one)

and K, are constant.

where is 14,

The output signals of the logarithmic amplifiers 5 and 10, due to the identity of the circuits, are directly proportional to the value of H — the temperature potential, which is a significant disadvantage of such logarithmic circuits, despite their simplicity, but since the differential transistor pairs of logars (| amplifiers 5 and 10 are under the same temperature conditions, then, as follows from (1), the indicator 6 indications do not depend on the temperature drift of the transfer coefficient of the logarithmic amplifier 5. At the same time, the reference voltage (s) supplied for the combined reference and signal inputs of logarithmic amplifier 10 may possess any type of instability in particular be temperature-unstable.

 Eliminating the zero error caused by the instability of the excitation current of the VTP 2, the operating frequency and the transmission coefficient of the amplifier-detection path can be applied to the reference input of the logarithmic amplifier 5, a voltage directly proportional to such parameters. Information about such parameters can be obtained by inputting, for example, a so-called test converter in the main ECP 2, whose output signal is directly proportional to the specified parameters. However, this technique significantly complicates the design of the VCP 2 and creates a number of inconveniences for the user. It is possible to eliminate such disadvantages by introducing into the thickness gauge a transformer 7 located in the instrument case and connected to the output of the autogenerator 1. At the same time, the output signals of amp312

The D and 9 volume detectors are directly proportional to the parameters, the instability of which creates a zero error. Taking into account the peculiarities of the logarithm scheme, it can be concluded that these factors do not affect the indicator readings 6.

Thus, the proposed device possesses a high accuracy of ejections due to a significantly higher temperature stability (the latter is determined only by the stability of the passive elements included in the thickness gauge blocks and nodes), which allows such devices to be referred to the group of so-called quasi-besatal thickness gauges, those. devices that will not require calibration in the process of working with them.

Claims (1)

Due to the complete independence of the display of such a thickness gauge from changes in ambient temperature, it can be used in a wide variety of temperature conditions. Invention Formula Eddy current dielectric coating thickness gauge containing post-Editor S. Patrusheva Order 875/40 Compiled by I. Rekunov Tehred M. Khodanich Proof-reader I. Erdeyi Circulation 678 Subscription VNIIPI USSR State Committee for inventions and discoveries 113035, Moscow, Zh-35, Raushsk nab., 4/5 Production and printing company, Uzhgorod, st. Project, 4 174 oscillator, eddy current transducer, amplifier, ultra-low detector, logarithmic amplifier and adder, voltage source and indicator, characterized in that, in order to improve measurement accuracy, it is equipped with a series-connected transformer, the input is connected to the output oscillator, a second amplifier and a second amplitude detector, and a second logar | A log amplifier, the logarithmic amplifiers are made adjustable, the second input of the first logarithmic amplifier is connected to the output of the second amplitude detector, the first and second inputs of the second logarithmic amplifier are connected to the source of the reference voltage, and the output is made in the form of an analog the digital converter to the reference input of which the output of the totalizer is connected and to the serial input - output first logarithmic amplifier.