RU1826052C - Vortex current flaw detector - Google Patents

Abstract

The invention relates to the field of non-destructive testing and can be used to detect or layers on titanium alloys. An increase in the reliability of control is achieved by choosing the operating point on the hodograph of the complex resistance of the eddy current transducer, which is correspondingly more sensitive to changes in electrical conductivity, by identifying the a-layers as thicknesses of the electrically conductive coatings, by reducing the number of turns of the eddy current transducer to the minimum possible, as well as due to the fact that the eddy current flaw detector, consisting of series-connected auto-generators with eddy current flow in parallel In the oscillatory circuit, detector and indicator, the inductance coil is turned on, the eddy current transducer is connected in series with the capacitor, and the inductance coil is connected in parallel with the eddy current transducer and capacitor, the inductance Li of the eddy current transducer is the inductance 1h of the inductor and the capacitance C of the capacitor is selected from the condition Јj-Ј- , wLi "0.1 th) 1 g, where wi 0.1 (O is the resonance frequency of the oscillatory circuit when the eddy current transducer is located above the non-magnetic conducting space stvom. 1 ill.

Description

The invention relates to the field of non-destructive testing and can be used to detect " layers on titanium alloys.

The aim of the invention is to increase the reliability of control.

Drawing A structural diagram of an eddy current flaw detector is given.

The flaw detector contains an oscillator 1, the oscillatory circuit of which consists of a series-connected eddy current transducer 4 and a capacitor 5 and a coil connected in parallel to them

6 inductance, the inductance of the eddy current transducer 4 being set as small as possible in order to reduce the gap between the turns of the transducer and the product under control. The resistance of the capacitor 5 is taken approximately by an order of magnitude greater than the inductive resistance of the eddy current transducer 4. The resistance of the inductor 6 is also taken by approximately an order of magnitude greater than the inductive resistance of the eddy current transducer 4. In addition, the resonant frequency of the circuit and the diameter

about

ate

Yu

the eddy-current transducer must correspond to the fact that when the a-layers are detected, the operating point on the hodograph of the inserted resistances of the eddy-current transducer located above the nonmagnetic half-space is in the range of the generalized control parameter 2 p 5. This corresponds to a resonant frequency of about 10 MHz and the eddy-current diameter converters about 1 mm. We assume that the value of the electrical conductivity of the titanium alloy is 0.7 MSm / m,

In this case, / R atafio 0.5-10 Зх

x 28 1C7 0.7 106 4 3.14 10 7 3.7.

In addition, the number of turns of the inductor should be minimal at which the oscillator generates oscillations, which corresponds to the maximum sensitivity of the oscillator to changes in the complex resistance of the oscillatory circuit. The output of the oscillator 1 is connected to the input of the amplitude detector 2, at the output of which the indicator 3 is turned on. Structurally, the oscillator and the amplitude detector are made on a printed circuit board, at the pointed end of which a eddy current transducer is wound.

Eddy current flaw detector operates as follows.

The oscillator 1 generates a sinusoidal voltage with a frequency of about 10 MHz. The converter is placed with a working end on the surface of a defect-free sample. The readings of the flaw detector indicator are substantially reduced, which indicates the great sensitivity of the flaw detector to the influence of the gap. By swaying the transducer in different directions, there is a minimum of flaw detector readings, which corresponds to the perpendicularity of the axis of the transducer to the surface of the monitored product. After that, the transducer is placed with the working end on the product to be monitored and, likewise, with the sway of the transducer, there is a minimum of flaw detector readings. Moreover, if the a-layer under the eddy current transducer is absent, then the readings of the flaw detector correspond to the readings of the flaw detector when the transducer is installed on the surface of a defect-free sample. If there is an “-layer under the eddy current transducer, then the readings of the flaw detector indicator will be shifted toward higher values, i.e. influence a. the layer is similar to the influence of the gap on the eddy current

converter. For example, if the thickness of the o: -layer is 50 μm and an M24 type microammeter is used as an indicator (maximum current value is 100 μA), then the change in readings from the influence of the or-layer is 20 μA, which allows moderate detection "-Layer on titanium alloys.

The principle of operation of a flaw detector is as follows. We denote: the complex resistance of the eddy current transducer 4 - Zi, equal to Ri - JcoLi. capacitance 5 - C, inductor La.

The complex resistance of the oscillating circuit will be determined by the formulas:

Rl + j (wLi-- - jtt) L2 Ri + J ((Li)

j Ri a La - w L2 (t Li -) Ri + j (wLi - 7Jc- + "L2)

At resonance, the following equality will be observed: win - ttg + WU

l)

the complex resistance of the circuit is equivalent and will be of the form: Z3

rwUCwLi--)

 J a) L2c The modulus of equivalent resistance will be defined as

o; L2 (

1

Shn-g-g

about C

Ri

) 2+ (1)

The contour has the following properties corresponding to the conditions for the detection of a-layers on titanium alloys.

If the parameters of the circuit correspond to the values of the resonant frequency of 20 MHz, then the circuit has good sensitivity to the influence of the gap on the eddy current transducer and practically no sensitivity to the influence of electrical conductivity, and in particular,--layers on the eddy current transducer. At the same time, significant sensitivity to the effect of capacitance between the controlled product and the housing (not shown in the diagram and formulas) on the eddy current transducer was noted. This effect results in the fact that if you touch a controlled product with a metal part, or simply

To move the eddy current transducer through the defect-free section of the monitored product, the indicator readings change. Based on this, the resonant frequency of the circuit and the diameter of the eddy current transducer are set so that the operating point on the hodograph of the complex resistance of the eddy current transducer is outside the range of influence of this capacitance and at the same time in the region of sufficient sensitivity to changes in electrical conductivity.

If the parameters of the circuit correspond to the conditions for the detection of α-layers by a flaw detector, then the resonant frequency of the circuit is approximately 10 MHz, the diameter of the transducer is approximately 1 mm, and the operating point on the hodograph of the complex resistance of the eddy current transducer is in the 2/5 region.

The inductive resistance of the eddy current transducer is approximately an order of magnitude lower than the capacitance resistance, i.e.

u) Li ssQ, 1 c and also approximately by pore -

doc less inductance L2. those. W LI 0.1 o).

Decreasing inductance L.2 increases the sensitivity of the oscillator to a change in the complex resistance of the oscillatory circuit

If the eddy current transducer is installed on a sample with a certain value of electrical conductivity a. then the inductance Li decreases, the resistance RI increases, as a result of which the modulus of the equivalent resistance 4 according to formula (1) decreases. If the eddy current transducer is installed in series on samples whose electrical conductivity values are correspondingly reduced, then the inductance value is. Li will increase accordingly, the resistance value RI will hardly change, and the modulus of equivalent resistance I 2e I according to formula (1) will decrease. Those. a decrease in electrical conduction affects the opposite of an increase in the gap, —the layers have a lower value of electrical conductivity in comparison with the base on which they are located. However, they influence the readings of the Flaw Detector, and consequently the module of equivalent resistance, not opposite to an increase in the gap, but of the same type. This is explained by the fact that the information parameter when detecting a-layers in a given flaw detector is not the electrical conductivity, but the thickness (.f-layer or thickness of the electrically conductive coating.

As a result, with the influence of the d layer, the inductance Li increases, the resistance RI decreases, and the modulus of the equivalent resistance IZ3 increases, which is similar to the effect of an increase in the gap.

Let us determine the depth of penetration of eddy currents into the controlled product.

(5

1

v n F a about

3.14 107 -0.7 -T55 4 3, 10

 190 μm

During testing, the flaw detector revealed all A. layers up to 200 microns thick.

A specific flaw detector has the following parameters. The oscillator is assembled on field-effect transistors KP302V and KP103M. The eddy current transducer 4 has 8. turns wound with a wire with a diameter of 0.07 mm, the inductance of the eddy current transducer is 0.08 μG. The diameter of the eddy current transducer is equal to one mm. We determine the inductive resistance of the eddy current transducer at a frequency of 10 MHz.

V „"

Http o) Li 6.28 10 0.08 - 5 ohm

The capacitance of the capacitor 5 is 280 pF. We determine the capacitance of the capacitor 5 at a frequency of 10.

Y --- -

Bs., /

TS 6.28 10 -28 10

-f.- r-57 ohm

The coil b has 50 turns wound with a wire with a diameter of 0.2 mm, the value of its inductance is 1 μG.

We determine the resistance of the inductance 6:

Xg b, 28 -10-1 62.8 ohms, we calculate the resonant frequency of circuit 1

E $ -

2 C (C + La)

1

2rcV280 1012 1.08 10 9.2 MHz

The flaw detector was tested for sensitivity to changes in electrical conductivity and for the detection of about. -layers.

The sensitivity to changes in electrical conductivity was tested on three standard certified samples with specific conductivity values of 0.54.0.71 and 0.925 MSm / m. Also, sensitivity to changes in electrical conductivity and to a-layers was tested on three samples with a-layers having specific conductivities of 9.59, 0.7 and 0.9 MSm / m. The samples are cylinders 10 m high, 25 mm in diameter, in the middle of one of the ends of which there is an a-layer circle, 4 mm in diameter. Approximate depth a - a layer of 20-50 microns. Tests were carried out in the absence of a gap and in the presence of a gap of 75 microns. A V7-16A millivoltmeter was used as an indicator. The output voltage of the flaw detector when the eddy current transducer was in the air was 612 mV.

It has been established that an increase in the electrical conductivity of the metal bases affects the gap increase of the same type, and the a layer also affects the gap increase of the same type. Voltage increments from the influence of a-layer,

Claims (1)

equal to 17-33 mV confirm that the flaw detector sensitivity is sufficient to detect a-layers. SUMMARY OF THE INVENTION A eddy current flaw detector comprising a self-contained oscillator, in which a eddy current transducer, detector, and indicator are included in a parallel oscillatory circuit. what. in order to increase the reliability of the control, it is equipped with an inductor, the eddy current transducer is connected in series with the capacitor, the inductance coil is connected in parallel with them, the capacitor C, the inductance LI of the eddy current transducer and the inductance La of the inductor are selected from the conditions ft) Li 0.1 1 ft) Li 0.1 cola, where o is the resonant frequency of the oscillatory circuit of the oscillator when the eddy current transducer is located above the nonmagnetic conducting half-space.