SU1536289A1 - Device for measuring depth of surface in conducting materials - Google Patents

Abstract

The invention relates to conductometric devices for measuring the depth of surface cracks in conductive materials and can be used to monitor carbon and carbon plastic composite materials. The aim of the invention is to increase the sensitivity and reliability of measurements. The electrode system consists of five electrodes, four of which are placed on a common movable base and are grouped as a gradient probe (one current and two measuring electrodes) with one additional measuring electrode located on a line perpendicular to the axis of the gradient probe current electrode. Removal of the additional electrode from the first current electrode is larger than the base of the gradient probe. The second current electrode is made structurally independent and is attached to the product under study. 3 il.

Description

The invention relates to means of electrical non-destructive testing of conductive materials and products and can be used to control the depth of surface cracks in carbon-graphite and carbon-plastic composite materials.

The aim of the invention is to increase the sensitivity and reliability of measurements.

FIG. 1 shows a functional diagram of a device for measuring the depth of surface cracks; FIG. 2 shows a horizontal projection of the structure.

devices; Fig. 3 shows a top view of the structure.

The device of FIG. 1 contains a stable current generator, a conductometric primary converter in the form of a common base 2 with electrodes 3-6, an independent electrode 7, a meter 8 and a recorder H. The meter 8 includes a differential gain-j or 10 and 11, a high-pass filter () 12, phase detector 13,

The current electrodes 3 and 7 are connected to the output of the generator 1. The measuring electrodes 5 and 6 are connected to

oh to

00

with

Directly to the first and second inputs of the meter 8, the first input of which is connected to the auxiliary output of the generator 1. The meter output is connected to the recorder 9, Electrode 7 is made structurally independent and can be attached to any point of the test surface. The electrodes 3-6 are fixed on a common base 2 (Fig. 2), with the electrodes 3 being current and 5, 6 measuring forming a gradient probe with a ba.oh r.j (fig.Z). An additional measuring electrode 4 is located on the 0-0 line, perpendicular to the axis of the 0-0 gradient probe and passing through the first current electrode 3, with the distance to it g / greater than the base of the gradient probe g.,. An additional measuring electrode 4 is connected to the fourth input of the meter 8. The first two inputs of the meter are the inputs of the differential amplifier 10, the output of which is connected to the first input of the differential amplifier 11, the second input of which is the fourth input of the meter 8, the differential output the amplifier 11 through the serially connected FZCH 12 and the phase detector 13 is connected to the output of the meter 8. The input of the reference signal of the phase detector 13 is the third input of the meter 8.

The device has a combination of gradient and potential probes oriented mutually perpendicular to the common current electrode. With this arrangement of the electrodes and the scanning direction, the surface crack first enters the zone of control of the gradient probe, while the potential probe tracks the background level on the defect-free surface determined by the electrical conductivity of the material. Thus, a compact system of two probes is formed, which has a small area the control and the probe of potential type are in contact with the surface of the object immediately close to the probe of the gradient type.

The potential-type probe is not sensitive to cracks perpendicular to the axis of the gradient-type probe, but it allows measuring the potential in the area immediately adjacent to the area being monitored.

one

one

0

five

0

five

ABOUT

five

0

five

0

five

The optimal ratios between r and g., Which meet the requirement of maximum sensitivity, were determined experimentally r1 (0.45-0.6) rz. , The device works as follows.

The independent current electrode 7 is attached to the test surface at any point along the scanning direction, but far from the base. total electrodes of the system (the distance depends on the dimensions of the products and can reach I m). Its role is to close the current paths coming from the stable current generator, and in order to reduce the noise level it is grounded, i.e. equalizes the potential of the instrument housing and the surface of the product being monitored. The frequency of the generator is set such that the depth of penetration of the floor into the material is minimal. Surface currents in the defect area follow its profile. In metals, the crack profile has a low roughness, and the current path is increased by an amount that, with sufficient practical accuracy, can be considered equivalent to twice the crack depth. In coal-plastic and carbon-graphite composites, the crack profile roughness is much larger than in metals, therefore the path traversed by surface currents along the profile of such cracks are significantly different from the doubled depth of cracks. If the oscillation frequency is set such that the depth of penetration of the field in materials is equal to or greater than the depth of cracks (the measuring range of which is specified), then the material in the control zone can be represented as successive layers (material-defect-material) with different resistivity: p ,, - pr, - p, where p1, the resistivity of the material and the defect; respectively, with p «p and p - const. In this case, the expression for the transfer function of the gradient probe when it crosses a crack of depth h has the form KP, + P4) 0

21G U)

voltage on the first and second inputs of the meter 8; current generator 1; base gradient probe (smf.Z);

U, where U, 51

1 is the distance between the electrodes 5 and 6,

For a potential probe type, in the zone of control of which the defect does not fall, the transfer function is:

U,

Ujl

(2)

where U j is the voltage on the fourth

input meter 8; g is the interelectrode distance (see Fig. 3).

Taking into account the locality of the electron probe control, we assume that there is no anisotropy of electrical conductivity in a controlled part of the surface; therefore, in the absence of defects, the parameter for both probes is equal to p. If 1 0.5 g., And g 7 0.5 g, then the resulting signal at the output of the differential amplifier additionally inserted into the device has the form

 rVi-Pi -k + rrfTt (3)

The primary transducer 2 is moved along the test surface by scanning it. The registrar 9 fix the signal U, - U 2, proportional to the depth of the surface cracks in the material.

362896

Claims (1)

Invention Formula A device for measuring the depth of surface cracks in conductive 5 materials containing a stable current generator, a four-electrode conductometric primary transducer, a meter and a recorder, the generator output connected to current electrodes, and the measuring electrodes connected to the first and second inputs of the meter, the output of which is connected to the recorder, and the third input of the meter  5 is connected to the generator output, characterized in that, in order to increase the sensitivity and reliability of measurements, the meter is equipped with an additional, fourth input, the electrodes of the primary converter are fixed on a common base and are grouped into a gradient probe, in which one current and two measuring electrodes are mounted on an additional measuring electrode, located on the line perpendicular to the axis of the gradient probe, passing through the first current electrode and remote from it by a distance greater than the base of the gradient probe, with the additional measuring electrode connected to the fourth input of the meter, and the second current 5, the electrode is structurally independent. 20 five 0