SU1682901A1 - Eddy current device for nondestructive testing - Google Patents

Abstract

The invention relates to a measurement technique, namely, to the field of non-destructive testing methods for materials, and can be used to measure the thickness of insulating coatings, such as enamel, paintwork and other applied, on conductive products. The purpose of the invention is to improve the accuracy due to the fact that the eddy current device for non-destructive testing contains a working and compensation eddy current overhead transducer with concentric excitation windings, a current generator. The working and compensating converters contain identical identical loop-shaped measuring windings, each pair of windings is placed in the same plane, and the windings in pairs are displaced relative to each other, the windings with the same radii on the working and compensating converters are connected in pairs opposite, and both pairs they are connected oppositely and the output is connected to the measuring unit, the radius values of the measuring windings yy correspond to the ratios rn / R b / 2R - 0.6 with rn R; R / rn 2R / 2R + b is 0.6 at R gp, and the radius R of the exciting windings of the working and compensating transducers is selected from the condition / 3 23-25. 8 il. WITH

Description

about soy about about

The invention relates to a measurement technique, in particular, to the field of non-destructive testing methods for materials, and can be used for testing and measuring the thickness of insulating coatings: enamel, paintwork and other coatings applied on conductive products.

The aim of the invention is to improve the accuracy of the device by reducing the effect of changes in electrical conductivity.

FIG. 1 shows an eddy current device for non-destructive testing; on

FIG. 2 - electric circuit of the device; in fig. 3 - eddy current transducer; in fig. 4 - the same, the embodiment; in fig. 5 and 6 are graphs, respectively, of the relative sensitivity of 4a (Ah) eddy current transducers to the insulation thickness Ah and to the electrical conductivity of the product 4 (7from the ratio of the radii of the transducer winding d -);

 l

- graphs of dependence 4а and 4а on the generalized parameter /, respectively.

The eddy current device for non-destructive testing consists of a working overlay eddy current converter (VTP) 1 and a compensation VTP 2, identical to the worker. Each of the transducers 1 (2) contains a cylindrical excitation winding 3 (4) connected to an AC source 5, and two loop-shaped and measuring windings (PIO) 6 and 7 (8 and 9), connected in pairs opposite, to form pairs of windings 6 , 8 and 7, 9, differential pairs of windings 6, 8 and 7.9 are also interconnected with each other and are connected to the common output to the measurement unit 10. Exciting windings 3, 4 and measuring windings 6-9 are placed on non-ferromagnetic and non-conductive cylindrical frames 11 and 12.

The radii R of the excitation windings of the working ECP 1 and the compensation ECP 2 are determined from condition 23-25 by the formula

R wfer- ™

where / 9 is a generalized parameter;

f is the frequency of the excitation current;

(J0 - electrical conductivity of the material of the reference product;

fio - magnetic permeability of vacuum,

and the radii rni, 2 corresponding measuring windings are selected from the conditions

- - 0.6 if rni.

2R

2R + b

- 0.6 if R hp1,2.

In operation, a working VTP 1 is mounted on a test article 13, covered with an insulating layer 14 of thickness Ah, and a compensatory VTP 2 is placed on a reference article 15 with a reference electrical conductivity of cr0. Series-connected excitation windings 3 and 4 are connected to an AC source 5 with a frequency f.

From the output of the differentially switched FEC 6 and 8, the absolute voltage change is determined, determined by the expression

A U.8 Us - U6 (4а Yes - 40) Ue.

(2)

where 4 (7, 4a is the relative sensitivity of the VTP 1 to the electrical conductivity of the product and the coating thickness Ah, respectively,

Since the loop-like windings 6,7 and 8, 9 are placed in the same plane with the exciting windings 3 and 4, respectively, the parameter

„2Ah-hp 2Ah, ..

a- R - R -W

where h0 is the distance between the exciting winding and the FEC (h0 0);

Ah- gap (or insulation thickness). In view of (3) for A K.

А 1) 6.8 U8 (408.6 - 40В.6) - (4)

With differential windings 7 and 9, the voltage D 119.7-1) 9 -U7 is removed

U9 (4., 7). (five)

When the reference signals Ue are equal - Ug, .b-Li is written for the resulting voltage.

 U (408.6 - 409.7) C + -S5 4ot 7 4oT to (I,

An analysis of the resulting formula (6) shows that the thickness control of the insulation coating A h can be performed under the condition

4e, 7 4ov, B. (7)

and the output signal from the eddy current device AU depends on Ah at

409, 6 (8)

At 4 ° 7. 7 a, b and 4 °, 7 4ov.b expression (6) takes the form

 (4ov.b-409.7). (9)

those. It is only determined by the value of Ah with Do const. Optimal control of the insulation thickness Ah at 4, b - 4 oe, 7 const (10)

when changing ft, in this case it becomes possible to exercise quantitative control without using calibration charts.

FIG. 5 and 6 are graphs of change

neither ((5) and 4o ($}. where d is for

(eleven)

Gp

R rn and

5.Јprigp (12)

where R, rn is the radius of the exciting windings 3 and 4 of the excitation and measuring windings 6, 7 and 8, 9, respectively. The dependencies 4a p (5) and 4a p (5) for the FEC (Fig. 5 and 6) are obtained for different values of the generalized parameter

/ 3 R T2jrf1 “o (f / o ± Yes). (13)

An analysis of the dependence 4a p (fl) shows that in the area of ft 15 for values of 5 0 - 0.6 A (const, and for the same values, 54a changes.

From FIG. 5 and 6, it follows that, for example, for a FEC with 5i 0.2 and & 0.6 with p 15 - 50 4o6i 4b2 and 4ea5i Qafa, i.e. conditions (5 and 6) are satisfied when the ratios of the FEC radii to the radius R are not equal to one another and are values lying in the range of 5.0-0-0.6.

Another condition for the equality of 4cb, c 4e, 7 is their independence from 0, which is equivalent to ensuring the same nature of the change 4, b f (f $) and (fi), since in this case 4, b - 4ot.7 0.

Analysis of the graphs (Fig. 5 and 6) shows that in the region (3 15-30 at 6 0 - 0.6 "dependencies 4, (D) and 4о9l RF) almost coincide, therefore in the specified range of values / difference Lov.e 4cb, 7 0. For example, if you select the FEC 6 and 8 with 5i 0.2, and the FIO 7 and 9 with 62 0.6, you get at 30 ft and 50 for 5i-0.2 4oB -0.42; 4 - 0.30:

for d 0,6 4о -0,41 4; -0.2 9. Then D4-0.01; D4sv-0.01.

In the range of ft from 15 and above, the difference is 4ov, b - 4o9j 0. On the other hand (Fig. 6), it follows that for the same values of / and d: 4, 12.6; 4-16 16.6 for 5i 0.2; 4.0 11.9; 4c® 15.9 dl (, 6.

Then D4 is 0.7, D4 ha 0.7 and conditions (10) are satisfied. FIG. 8 and 7 are graphs of dependencies Aa (Ah) / (p) and 4st y (D), constructed from the dependences shown in FIG. 5 and 6. From the dependences it follows that for values (5 0 - 0,6, a rational value of D is 23 - 25, since in this case 4o6i 4ob2 and 4odi - 4 «5г 0.

In the same range of values of / (Fig. 8) in the range of values of d 0 - 0.6, the difference is 4o5i - 4co52 const, for example, for 5i 0.2 and 52-0.6 4o6i -4oI2 1 The rational range obtained

values of D, defines em and rational

excitation winding radius R:

R -23-25.,.

to

The eddy current device allows nondestructive testing of insulation coatings with almost complete

suppressing the interfering factor — changes in the electrical conductivity of the product material in a wide range. For example, reference value a0 30 10 cm / m, / 3 24. excitation current frequency f - 600 10 Hz, range of / JOT 24 to 30 and 18. i.e. , taking into account the adopted parameters, for the radius of the excitation winding of the coi die, (14) receive P - 2 mm

The radii of the PIO 6 and 8 when R i p for d 0 2

Gp6.8 Yu MM, FOR & 2 0.6

GY9.7 - § 0,33 MM.

5 The range of change in the values of the electrical conductivity of a material for which the detuning from their influence is made is determined by

20

a + d d lЈ ± .M) L - 4b, 84 cm / m; , “O

O- M @ -AjL 1b, 8b cm / m;

 2 I f R2 // o Relative change o is

thirty

(, 13%; .8%.

As follows from FIG. 7 and 8, this provides the condition of practical control, with a maximum error of measuring the coating thickness of 2.5% when the conductivity varies from 30 to 46.84 -10

cm / m and with an error of the order of 3% when changing aot 30 to 16.86 --106 cm / m. The measurement error of the insulation thickness by changing the coefficients 4a (Dm) w.bi 4a (Dm) d. when changing P for

the account is practically excluded since 4Ah8,6-4h9.7 const. This allows the meter to be programmed directly in units of measured coating thicknesses and used in a wide range of variations of Ah, while the known device allows the use of a converter with an R 2 mm to control coating thicknesses of no more than 100 microns.

Claims (1)

Invention Formula Eddy current device for non-destructive testing, containing identical working and compensating eddy-current overhead converters, each of which is made with a cylindrical exciting winding and two measuring windings, one of which is loop-shaped, characterized in that. that, in order to increase accuracy, the second measuring winding of each of the converters is loop-like and has a radius different from the radius of the first measuring winding, windings of the same radii of both converters are included in pairs in series-counter, pairs of measuring windings / FIG. 2 0 They are connected in series and counter, their free terminals are intended to be connected to the measuring unit, the radius R of the exciting winding is chosen from the condition 25, where / J is a generalized parameter, and the radii hp1.2 of the corresponding measuring windings are chosen from Gp1,2 / R b / 2R-0,6, if yyyyy R and R / rni, 2 2R / 2R + D - 0.6, if R rni, 2 where b is the width of the loop-like winding. 4a 12 It ten X X X X L X X / & & -. 3.6 X 0.7 X 7 X