SU1221572A1 - Electromagnetic method of measuring specific electrical conductivity of articles - Google Patents

Abstract

The invention relates to the field of non-destructive K: ontrol and can be used to measure the electrical conductivity of non-ferromagnetic conductive products. The purpose of the invention is to improve accuracy by suppressing the effect of gap changes. The method; measuring the electrical conductivity of the products consists in installing the reference eddy current transducer over the reference and controlled products with three fixed gap values, measuring the orthogonal component of the output voltages of the eddy current transducer for each gap value, determining the ratio the increments of the orthogonal components for two pairs of gaps: the maximum average and the average - the minimum, change the frequency of the exciting current. until the obtained ratios are equal, and use the obtained frequency value to determine the specific electric conductivity of the product. 2il. V g to to SP ND

Description

The invention relates to methods for non-destructive testing and can be used to measure the specific electrical conductivity of non-ferromagnetic conductive products with increased accuracy under conditions of significant changes in the gap between the eddy current transducer and the controlled product.

The purpose of the invention is to improve the measurement accuracy by suppressing the effect of gap changes.

FIG. 1 shows a block diagram of a device implementing the proposed method; FIG. 2 shows the hodographs of the relative applied voltage of a patch transformer eddy current transducer as a function of generalized parameters oi.

: R. "

where h is the gap between the eddy current transducer and the product; R is the radius of the maximum winding of the converter; W - circular frequency of the exciting current of the converter; / and "41f .10 n is magnetic constant; d - specific electrical conductivity of the product.

The device contains a function generator 1 with an adjustable output signal frequency, connected via a controlled switch 2 to the excitation windings of a system of identical (with equal radii of windings) transformer eddy current converters 3, 4 and 5 located coaxially on the plant (0.1 -0.2) 8 from each other, the measuring windings of which through the control switch 6 are connected to the i input of the variable voltage amplifier 7, the output of which is connected to the working inputs of the synchronous detectors 8 and 9, the reference inputs of which are connected They are connected to the outputs of the former 10 of the reference coordinate system j connected with its input to the second output of the function generator 1 with an adjustable frequency. The outputs of the synchronous detectors 8 and 9 through analog-to-digital converters 11 and 12 are connected to the block 13 random access memory devices (RAM), the outputs of which are connected to the inputs of the computing device 14, the output of which is connected to the control unit through a digital-to-analog converter

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equalizing input of the function generator with adjustable frequency. The generator 16 clock pulses through the counter 7 is connected to the control inputs of the switches 2 and 6, the address input of the RAM unit 13 and the input of the write pulse generator 8, the output of which is connected to the write enable input of the RAM unit 13.

10 The output of the variable-frequency function generator 1 is also connected via the frequency converter 19 to the code to the inputs of the computing device 20 and RAM 21, and the outputs of the RAM 2 and the permanent storage device (ROM) 22 are also connected to the inputs of the computing device 20, the output which is connected to the information input of the digital indication block 23, to the control input of which the output of the computing device 14 is connected, also connected via the imager 24 write pulses and the switch 25

25 modes of operation of the device to the input resolution recording RAM 21,

The method is implemented as follows.

Pre-write to ROM

2P 22 the numerical value of the specific elec-. tric conductivity of reference sample Cz 5t Install the system of eddy current transducers 3, 4 and 5 on the reference sample with some installation clearances about (in Fig. 2, oij is the relative gap between the lower eddy current transducer and the product under test). The switch 25 modes of the device closes, which corresponds to the mode of operation Calibration.

A clock generator 6 triggers a counter 17, which generates control codes for switches 2 and 6, which are also RAM address codes 3 and are used in shaper 18 to generate recording pulses. Managed switches 2 and 6 with a clock frequency following alternately connected to the exciting windings of eddy current transducers 3, 4 and 5 output sinusoidal

S is the voltage of the functional generator with adjustable frequency, and their measuring windings (synchronously with the exciters) are input usi5

The unit has an alternating voltage, which is equivalent to moving one eddy current transducer to fixed heights. The output signals of the synchronous detectors 8 and 9 are proportional to the orthogonal components of the input (output) voltages of the polled eddy current probes 3, 4 and 5 in figure 2.

X ,, 9 J g and g V i i, respectively, are converted by analog-digital converters 1 1 and 12 into a binary code. They are written into the memory cells of the RAM unit 13. The reference voltages for synchronous detectors 8 and 9 produce the reference coordinate system shaper 10, which is triggered by a pulsed rectangular voltage of the function generator 1 with adjustable frequency and forms a pair of rectangular voltages that are shifted relative to each other 90 and rigidly synchronized with the voltage power eddy current transducers

The computing device 14, using the information accumulated over the three cycles of operation in the memory cells of the RAM unit 13, calculates a function of the form

Hi-ji

x, x

 (/,about):

where IJ k is the value determined by the ratio of the conversion coefficients of the output signals of eddy current I transducers in the channels of synchronous detectors 8 and 9. The function Ф (/, cio is the difference of the tangents of the tilt angles of the straight lines carried through points on the complex plane of the applied stresses ( Fig. 2), corresponding to some value of the generalized parameter / and relative gaps j and, 2

moreover, oi} (x: ,, 0 3 ° 1 os, + 2uci, where l o (, is the relative distance between eddy-current transducers 3 and 4, 4 and 5. As it follows from the hodographs of the applied voltages of eddy-current overhead transformers (Fig. 2) at some optimal value of the generalized parameter / 5 / 5opg, the retraction line becomes direct in the range of variation of the relative gap

oi, a, 1 ... 1, 0, and at / 5/3

wholesale

and

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L; / Hz отв of the withdrawal line has a curvature of opposite signs, which determines the following properties of the function F (f, oiig): 5 fO eu.

S (p, 0. With O, if

in the range of change of the installation 10 gap aio o, 1. .. (l-2iot).

The function F (/ 5,) differs from .OI) by the multiplier, which remains almost constant during the measurement. Digital1 tax

15 converter 15 converts with

taking into account the sign of the digital value f (p, o} to the voltage that is applied to the control input of the function generator 1 with adjustable frequency,

20 and if the function F (/, tig is positive, then the frequency decreases, and if it is negative, it increases and, therefore, approximation of the parameter 25 occurs;, in (u7cr | opt) Poll Cycles of Eddy Current Transducers 3, 4 and 5, the calculations of the function K (/ 1, (d) and the changes in the operating frequency of the functional: generator 1 continue automatically, and the frequency changes until the value of the function F (p.et). At the output of the computing device | Va 14 does not vanish, i.e.

35

fi

where {, is the steady-state value of the operating frequency.

Frequency converter 19 to code continuously converts the operating frequency of function generator 1 into a parallel binary code that enters the inputs of computing device 20 and RAM 21. Computing device 20 performs the operation of dividing the number recorded in RAM 21 by numbers, which codes arrive from the frequency converter 19 in the code, and multiplies the result by the numerical value C), t stored in ROM 22. At the moment that the function F (p, oio) is zero, the output of the computing device 14 at the output of the computing device 14 is Pulse records that

through the closed switch 25 of the device operation modes sends a pulse to the input of the write permission of the RAM 21, as a result of which

the numerical value of frequency i, is recorded. At the same time, the readings of the digital indication unit 23 are displayed, the information input of which receives the output code of the computing device 20. As in the calibration mode, from the converter 19, the code and RAM 21 to the inputs of the computing device 20 receives the code of frequency values 1, then the digital 23 The display will show the numerical value of th ,. This completes the calibration process of the device, the essence of which is to write in the ROM 22 the numerical value d, and in the RAM 21, the corresponding frequency i,.

 The switch 25 modes of operation of the device open, which corresponds to the mode of operation Measurement. The system of eddy current transducers 3, 4, and 5 is installed on a controlled product with an unknown value of electrical conductivity ijj (, the device operates as in the calibration process 1 but unlike it, the frequency 21 is already recorded in RAM 21 computing device 14, the operating frequency of the function generator {takes a certain value ij and, according to condition (2), has

fr nt Rls izpo.

Wg

Equating the expressions for, we express the desired value;

 . . i, x -, .- p.

This function is implemented by the computing device 20, and the measurement result is shown by the digital display unit 23.

The invention allows to eliminate the error caused by fluctuations of the installation gap in a certain range determined by the radius R of the external windings of the converters.

and distance C between the converters ,. For example, since the possible range of fluctuations of the relative ustarhovchnogo gap oi, p is 0.1 ... (l-24 (t.), Then for R 6 mm and d sat 0.3 we get C iuci 0.9 mm and the range possible fluctuations of the installation gap uh - (l-2k) -0, l R 0.9 mm,

at R to 6 0.3; C, 5 mm and i h I, 5.

Claims (1)

Invention Formula Electromagnetic method of measuring the specific electrical conductivity and limit 5, consisting in the fact that the invoice eddy-current transducer is moved along the normal to the standard-komz and controlled products, change the frequency of the exciting current eddy current transducer, frequency values are measured that correspond to a given constant ratio of the parameters of the output signals of the eddy current transducer for: the reference and monitored products, respectively, and use the indicated frequencies to determine the specific electrical conductivity of the monitored products, which is the case. 4TOj, in order to improve measurement accuracy by suppressing the effects of gap changes, the eddy current transducer is installed over reference and monitored MM products with three fixed the values of the gaps are measured for each value of the gap orthogonal components of the output voltage of the research institute of eddy current transducer, determine the ratio of the breakdowns of the orthogonal components, SC1 of two pairs of gaps: the maximum — medium and medium-minimum 5; and, by varying the frequency of the exciting current of the eddy current transducer, Fiel L; / 7.2 / g 0.3 Xs 0, USH Rf-y (jo  Ush Rf-y (jo Rept Fi.2 VNIIPI Order 1605/50 Circulation 778 Subscription Branch PPP Patent, Uzhgorod, ul. Project, 4