GB2224575A

GB2224575A - Displaying features (eg defects) of an electrically conductive component

Info

Publication number: GB2224575A
Application number: GB8825886A
Authority: GB
Inventors: David Anthony Topp; Martin Christopher Lugg
Original assignee: Technical Software Consultants Ltd
Current assignee: TSC Subsea Ltd
Priority date: 1988-11-04
Filing date: 1988-11-04
Publication date: 1990-05-09
Anticipated expiration: 2008-11-04
Also published as: GB2224575B; GB8825886D0

Abstract

A movable probe array 12 whose position is tracked 14 is used to investigate features (eg defects and their locations) of a component 11. The array has both ac field detecting elements contacting the component surface, and non-contacting elements sensing the surrounding magnetic field. Different frequencies of an induced or injected field are used to vary the depth of inspection. A visual display is generated. <IMAGE>

Description

Electromaqnetic Microscope This invention relates to a microscope and more particularly to a microscope for evaluation of features of an electrically conductive component by means of a technique whereby the component is subjected to an alternating electrical current (ac) and surface ac field, or associated magnetic field, is measured to provide a value indicative of a feature being evaluated.

The technique is known as a method of measuring crack depths in electrically conductive workpieces and is disclosed in United Kingdom patent specification No. 2 012 965. The measurements depend on the existence of 'skin effect' whereby when an alternating current is passed through a metal component most of the current is carried within a peripheral portion of the component which extends to a depth given by::

where s = skin depth of current flow defined as the point at which the voltage falls to a value lie Cl.e. 0.368) of the voltage at the surface (m) cuirnt (Hz) f = frequency of altematina = relative magnetic permeability of component o = ' conductivity of component (mho/m) #. = 4xIO7 (H/m) X = 3.1416 It is an object of the present invention to utilise and extend this technique so that features of an electrically conductive component may be evaluated.

According to the present invention there is provided a microscope for evaluating a feature of an electrically conductive component comprising means for generating a multi-frequency ac field in the component, a movable device for sensing distribution of the field and for generating first signals indicative of field intensity, means for monitoring movement of the device relative to the component and for generating second signals indicative of location of the device relative to the component, means for comparing the first and second signals and for generating third signals and visual display means responsive to the third signals for displaying data indicative of said feature.

The said third signals may be indicative of detection of a defect in the component and location of the defect in the component.

The said third signals may be indicative of detection of variations in magnetic permeability and hence chemical composition of the component.

The said third signals may be indicative of detection of mechanical and/or residual stress in the component.

The said third signals may be indicative of detection of shape and thickness of at least part of the component.

Following is a description, by way of example only and with reference to the accompanying drawings, of one method of carrying the invention into effect.

In the drawings: Figure 1 is a circuit diagram of an embodiment of a microscope in accordance with the invention, and Figure 2 is a diagrammatic representation of a component the features of shape identification, thickness measurement and edge location of which are being evaluated by the microscope shown in Figure 1.

Referring now to Figure 1 of the drawings, there is shown an electromagnetic microscope 10 for evaluating the following features of a component 11 of electrically conductive material: (a) Defects such as flaws in surface or internal structure (b) Geometry such as shape and thickness (c) Magnetic and/or chemical composition (d) Mechanical and/or residual stress The microscope comprises a carrier 12 carrying first and second series of probes (not shown) in a ten by ten array.

The probes of the first series are disposed so as to contact a surface of the component 11 and the probes of the second series are disposed so as to be spaced from the component 11. The carrier 12 is movable relative to the component 11 under control of a probe position driver 13 which itself is under control of a probe location monitor 14. The first series of contacting probes are included in a circuit for measuring an ac electrical field injected or induced in the component 11 and the second series of non-contacting probes are included in a circuit for measuring an associated magnetic field. Measurement is effected by means of a transputer 15 which receives signals from the probes, the signals having been amplified by an amplifier 16 and routed to the transputer 15 via a multiplexer 17.The ac field is injected or induced by means of a unit 18 comprising an oscillator and an automatic control circuit to maintain the current. The oscillator is under digital control to give a multi-frequency output.

The transputer 15 includes a plurality of boards 1 to 6. The board 1 is a processor board which effects control of the multiplexer 17 and the probe location monitor 14; the board 2 is a processor board which effects control data interpretation and manipulation in accordance with signals (which contain amplitude and or phase information) received from the probes; the board 3 is a processor board which effects control of ac excitation; the boards 4 and 5 are also processor boards and provide graphical presentation by way of a visual data unit (not shown), the board 4 providing graphical representation and the board 5 being a fast graphics processor; the board 6 is a printed circuit board and is an interface with a keyboard (not shown) of a personal computer and provides an overall control function, fault detection and is a performance monitor.

In the example shown in Figure 1, the component 11 is being evaluated for (a) above, ie flaws in surface or internal structure. The carrier 12 thus is moved systematically relative to a surface of the component 11 by the position driver 13 in accordance with an algorithm for array data locating matching so that the whole of the surface is sensed progressively by the first and second probes carried by the carrier 12. Simultaneously with this process, signals are continuously monitored from the probes by the data interpretation and manipulation processor board 2 and, in accordance with algorithms for signal inversion to give defect detection, signals are transmitted to the boards 5 and 6 whereby visual display showing defect size and location is provided on the screen of the visual display unit.

Considering the formula set out above, it will be appreciated that varying the frequency f of the alternating current will give a variable skin depth which can be adjusted for assessing different thicknesses of the component 11 or different depths within the component 11.

Thus, by carrying out successive sweeps of the carrier 12 relative - to the surface of the component 11 and progressively adjusting the frequency f of the alternating current, values indicative of the mass of the component 11 can be established indicating any flaws therein.

In Figure 2 there is shown the carrier 12 of the microscope 10 and a component 19 the shape and variations in thickness (t1 and t2) of which are being evaluated. The carrier 12 is moved systematically relative to the surface of the component 19 by the position driver 13 in accordance with an algorithm for array data location matching so that the whole of the surface is sensed progressively by the first and second probes carried by the carrier 12. Simultaneously with this process, signals are continuously monitored from the probes by the data interpretation and manipulation processor board 2 and, in accordance with algorithms for signal inversion to give various details of component shape and location, are transmitted to the boards 5 and 6 whereby visual display showing details of component shape and thickness is provided on the screen of the visual display unit.

It will be appreciated that algorithms can be devised whereby the microscope 10 is capable of measuring magnetic and/or chemical composition and/or mechanical and/or residual stress in a component.

It will also be appreciated that the transputer provides a facility whereby measuring and interpreting both electrical and magnetic field perturbations simultaneously is possible together with fast switching linked to multiple channel input and fast data collation. The facility provides for pseudo real time visualisation of an electrical and/or related magnetic field.

Furthermore, it will be appreciated that evaluation of features of an electrically conductive component can be effected using a microscope in accordance with the present invention without the need for data input other than measurements of surface potential.

Claims

1. A microscope for evaluating a feature of an electrically conductive component comprising means for generating a multi-frequency ac field in the component, a movable device for sensing distribution of the field and for generating first signals indicative of field intensity, means for monitoring movement of the device relative to the component, means for comparing the first and second signals and for generating third signals and visual display means responsive to the third signals for displaying data indicative of said feature.

2. A microscope as claimed in Claim 1 wherein the third signals are indicative of detection of a defect in the component and location of the defect in the component.

3. A microscope as claimed in Claim 1 wherein the third signals are indicative of detection of variations in magnetic permeability and hence chemical composition of the component.

4. A microscope as claimed in Claim 1 wherein the third signals are indicative of detection of mechanical and/or residual stress in the component.

5. A microscope as claimed in Claim 1 wherein the third signals are indicative of detection of shape and thickness of at least part of the component.

6. A microscope for evaluating a feature of an electrically conductive component substantially as hereinbefore described and as illustrated in the accompanying drawings.