SU1635729A1 - Eddy-current flaw detector - Google Patents

Abstract

The invention relates to non-destructive testing and can be used for the inspection of electrically conductive objects. The purpose of the invention — an increase in the reliability of the control — is achieved by simultaneously suppressing the influence of the variation of the working gap of the eddy current transducer and the specific electrical conductivity. By adjusting the resistor 6, the sensitivity of the measuring bridge to the variation of the working gap of the eddy current transducer 5 at the lower frequency fi is suppressed. Generated by the generator 1. The suppression of the influence of the variation of the gap at the frequency fa is performed using the adjustment unit 11, made in the first embodiment as a phase shifter. By adjusting the gains of the amplifiers 13. 14, the suppression of the effect of the specific electrical conductivity on the voltage recorded by the inductor 18 is achieved. 2 Cp f-ly, 5 ill.

Description

The invention relates to non-destructive testing and can be used to detect subsurface defects in electrically conductive non-magnetic products.

The purpose of the invention — an increase in the reliability of the control — is achieved by simultaneously suppressing the influence of the variation of the working gap of the eddy current transducer and the specific electrical conductivity.

FIG. Figures 1 and 2 show the block diagrams of the eddy current flaw detector for various variants of the adjustment unit: FIG. 3 is a vector diagram of the reduced resistances of the bridge, corresponding to the mode of detuning from the effects of changing the gap; in FIG. 4 is a vector diagram of bridge voltages corresponding to the mode of detuning from the influence of gap measurement; FIG. 5 is a vector diagram of the bridge resistances under the influence of changes in electrical conductivity.

The eddy current flaw detector contains the lowest 1 and highest 2 frequency generators mixer 3. connected by first and second inputs to generators 1 and 2, respectively, power amplifier A, connected by an input to the output of mixer 3, a measuring bridge, the first measuring arm of which is formed by a eddy current converter 5, and the second measuring arm - serially connected variable resistor 6 and the first coil 7 inductance, the common point of the measuring shoulders is the first input top of the bridge, the first and second auxiliary s years echi bridge formed by the second and

ABOUT

so VI h o

The third coils 8 and 9 of the inductance, respectively, the common point of the auxiliary arms of the bridge is the second input peak of the bridge, which is grounded.

The flaw detector also contains a separation transformer 10, an adjustment unit 11, a selector 12 connected to the output of an isolation transformer 10. Its primary winding is connected to the output diagonal of the measuring bridge, voltage amplifiers 13, 14 connected to the corresponding outputs of the selector 12, amplitude detectors 15, 16. an adder 17 connected by corresponding inputs through amplitude detectors 15. 16 with outputs of amplifiers 13 and 14 respectively and an indicator 18 connected to the output of adder 17. Unit 11 This can be made in the form of a phase shifter connected between the output of the generator 2 and the common point of the coils 7. 9 inductance (see Fig. 1). In another embodiment (see Fig. 2), the adjustment unit 11 is in the form of serially connected variable resistor 19 and capacitor 20 connected between a common point of eddy current transducer 5 with a variable resistor 6 and a common point of coils 7. 9 inductance.

The inductance of inductance coil 7 is selected 10-15% more than the inductance of eddy current transducer 5 installed on the object to be monitored and powered by a low frequency voltage fv. In the second version, the maximum value of variable resistor 6 should be approximately 25% of the inductance of coil 7 inductance at frequency fi, the maximum value of variable resistor 19 should be about 10 times greater than the maximum value of variable resistor 6, and the capacitance of capacitor 20 at higher its frequency h should be about 1.5 times less than the inductive resistance of inductor 7.

Eddy current flaw detector works as follows.

Generators 1 and 2 produce voltages of the lowest f 1 and the highest f2 frequencies, respectively. The voltages are applied to the mixer 3, amplified by the power of the amplifier 4 and fed to the input of the measuring bridge. The resistor 6 is adjusted in such a way that the dien vector moves around the circumference when the gap changes (see Fig. 3), which corresponds to the absence of sensitivity of the bridge in terms of voltage fi to the change of the gap. At the same time, at the frequency fa, the point di shifts to the axis of the reduced inductive resistances to the point dz (as the denominator of the reduced active resistance of the resistor 6 increases, and the numerator remains constant), and the point ci to the point C2. FIG. Figure 4 shows a vector diagram of bridge voltage with frequency f2 for tuning away from the influence of the gap at frequency h with the help of adjustment unit 11. In the first embodiment, the phase shifter is adjusted for this by supplying part of the voltage from generator 2 to point d. in the second variant, the potential of point d is changed due to the shunting of the second measuring arm of the bridge with a chain of variable resistor 19 and capacitor 20. Both technical solutions are approximately equivalent. As a result, the potential of the point dj moves to the point d21 in such a way that the vector d2 c2 on the complex plane of the bridge voltages moves circumferentially as the gap changes. As a result, at frequencies f 1 and f2, it is possible to rebuild itself from the influence of changes in the gap from 0 to 2 mm on the output voltage of the bridge. After that, the output voltage f i and h is applied to the isolation transformer 10, from which it enters the input of the selector 12. In which the voltage voltages f i and f 2 are separated. From the outputs of the selector 12, voltages are applied to amplifiers 13 and 14, after which amplitude detectors 15 and 16 are detected and fed to the inputs of an adder 17, in which the voltages are subtracted. By adjusting the gain factors of the voltages applied to the inputs of the adder 17. The voltage from the influence of the electrical conductivity at the output of the adder is not applied, after which the voltage is applied to the indicator 18.

Let us prove the possibility of detuning from the effect of changes in electrical conductivity. We denote the resistance of the eddy current transducer 5 at the frequency fi-Zi, at the frequency fj-Zi1. resistance of resistor 6 - RZ, inductance of coil 7 -. inductance of coil 8 -, inductance of coil 9 - U.

In this case, if the bridge is brought out of equilibrium only by changes in the resistances Zi and Zi1. the eddy current transducer 5, then the reduced output voltages of the bridge at frequencies fi and h will be determined by the formulas

 K 1

AZi

Zn

U out2

Claims (2)

Claim 1. Eddy current flaw detector containing high and low frequency generators, a mixer connected by inputs to the corresponding generators, a power amplifier connected to the output of the mixer, an eddy current converter, a series-connected selector, a voltage amplifier, an amplitude detector, an adder and an indicator and connected between the second output of the selector and the second input of the adder are serially connected second voltage amplifiers and an amplitude detector, characterized in that. In order to increase the reliability of the control, it is equipped with a variable resistor, three inductors formed by a measuring current sensor transducer, an isolation transformer and an adjustment unit, the first and second measuring arms of the bridge are formed by a eddy current transducer and connected in series by a variable resistor and the first inductor, respectively. 0 five 0 five The first and second auxiliary shoulders of the bridge are formed by the second and third inductors, respectively, the common point of the measuring arms and the common point of the auxiliary measuring arms form the input vertices of the bridge to which the output of the power amplifier is connected, the bridge output is connected to the primary winding of the isolation transformer, the secondary winding of which is connected to the selector input, and the output of the adjustment unit is connected to the output top of the bridge, formed by the common point of its second measuring and auxiliary th shoulders. 2. Flaw detector pop. 1. distinguishing - with the fact that the adjustment unit is designed as a phase shifter connected by an input to the output of a high-frequency generator. 3 flaw detector according to claim. 1, characterized in order. that the adjustment unit is designed as a series-connected variable resistor and a capacitor and is connected by an input to an input top of a bridge connected to an eddy-current transducer. Fig 2 where Л Zi and AZi are increments of complex resistances Zi and 2.1 eddy current transducer at frequencies fi and h. corresponding to the vectors dici and d2C2 (see Fig. 3). J W1 L4 (R2 + jonLi) z, t, R2 + JW1L2 + Z4, + JW1L4 JftJ2 L4 (R2 + i21-2) gf R2 + j Wat-2 + 2f + L4 where 2f is the output resistance of the phase shifter. Zn Zi + AZ 1 + j & l L z: z n z i + Az i + jW2 La: After moving point d2 to point d21 by adjusting the phase shifter 11 on the complex plane of the bridge voltage, as follows from the vector diagram shown in FIG. 4. reduced output - Li output 2; bridge voltage –y-can be exported in2 to make a formula U out2  to Az1U It where AZi is the increment of the complex resistance Zi at the frequency f2, corresponding to the vector d2 C2 in FIG. 3 It is easy to show that the modules of the reduced output voltages of the bridge at frequencies f 1 and f2 will be determined by the formulas U 8YHG. j IAZ 1; TIHTG1 MU7Tj: lAZ Z n In this case, if the modules of the complex resistance Zi and Zi of the eddy current transducer receive additional increments from the influence of electrical conductivity ± / AZi / a and / D Zi / h, then equations (1) and (2) take the form U.-. / to | luZ.lilAZ./G | / and „, GG Ш; T & / „I Az, / iMz: / fj TgdaVD five 0 five 0 five 0 five 0 The voltage at the output of the adder 17 with equal gain factors of the voltages applied to the inputs of the adder will be proportional to the difference of the modules of these voltages, i.e. / g AZi / „it / Az.lCT e-N + K p7, M JllfihftlG / K zblfufe1 The principle of detuning from the effect of a change in conductivity is explained by the vector diagram shown in FIG. 5, where and AZ are the modules of the increments of resistance of the eddy-current transducer from the increments of the generalized control parameter fi at frequencies fi and f2 with decreasing conductivity σ, corresponding to the vectors nici and П2С2, respectively, - / Л Zi / о п - / Д Zi / (Т - increments of resistive modulus AZin AZ / from the effect of decreasing on frequencies fi and f2 corresponding to the vectors of pit and m2P2, respectively. / AZft / a and / AZfi / g; increments of resistive modules Zu and Zn from the effect of decreasing on frequencies fi and f2 corresponding to vectors hm and 12П2, respectively. The triangles mmici and gp2p2s2 with small increments of values and A Z can be considered rectangular. It follows from the mmici and gp2P2C2 triangles that if the values of / AZ / i / and / are changed (proportional, then the values of / AZi / a and / AZ / / a will also be proportional. From equation (3) it follows that / A Zi / o "/ Zn / ± / AZn / o and / / a / Zii / ± / AZnV. Therefore, the increments of the resistances ± / AZii / dn / AZn / fT in the denominator of the second and fourth terms of formula (3) can be ignored. In this case, it is possible to select the voltage gain factor S of the low-frequency channel in such a way that the voltage at the output of the adder will not depend on the values of / AZi / au / a. those / 42, /, + kz, l) n tmz-jo + S K - u: ilkz .lG iv i IMJ / ,. I i / az / Thus, with variation of the electrical conductivity a, the recorded signal remains almost unchanged. Figz