Ultrasonic system of distant determination of fault detector’s measuring transformer coordinates

ULTRASONIC SYSTEM OF DISTANT DETERMINATION OF FAULT DETECTOR’S MEASURING TRANSFORMER COORDINATES

Gudz Sergii

National Technical University of Ukraine “Kyiv Polytechnic Institute”

Instrument-making faculty, master of non-destructive testing

A problem of coordinate recording of initial information for fault detectors with the «manual» scanning of surface of controlled objects is not new for modern non-destructive testing. For the solution of this problem the bunch of major foreign companies offers their developments that allow determining the coordinates of position of measuring transformer in the process of testing [1].

The main direction of solution of the put task is the use of the non-contact ultrasonic and optical measuring systems. In any case determination of relative coordinates of planar position of measuring transformer to the fault detector takes place.

The principle of work of ultrasonic system is based on emission of acoustic oscillations with two acoustic emitters which are situated on the surface of measuring transformer of fault detector and reception of oscillations with two acoustic transceivers, which are situated on the measuring base. The height of emitters and transceivers is got out from a condition of avoidance of coordinate’s determination errors due to reverberation signals reflected from the surface of object being tested. For emission and reception of ultrasonic waves small bimorph airily-acoustic transformers of Sencera company are used (C4016 – open type). They work on 40 kHz  frequency. The radiation pattern has an aperture of approximately 60°; the wave length of oscillations presents about 8.5 mm midair [2,3].

The emission of radio impulse oscillations is produced by both emitters simultaneously, for the sake of expansion of radiation pattern of emitters they are located with 45° angle between them, thus taking into account ceiling, general radiation pattern presents approximately 110° [3,4,5].

Emitted radio impulse oscillation passes distances l1 and l2; these distances are determined by measuring the time delays τand τ2 on each distance. Thus measuring time delays and knowing the speed of ultrasonic waves spreading midair we can define the distances  and . Coordinates of measuring transformer location on plane comes in (the following equations:

,   ,

where B is the width of the measuring base.

Precision of coordinates’ evaluation first of all depends on speed of ultrasonic waves spreading midair and changes of temperature, so . For example, thermal change from 0°C to 25°C caused change of Cair from 331.6 m/s to 346.6 m/s. Thus ignoring an actual speed may cause significant errors. These errors could reach 0.1 m for such change of temperature.

Advantages of using such system are: compactness of transceiving-emitting elements of device; high antijammingness; protracted term of exploitation; simplicity of use; comparatively small cost; practically instantaneous readiness for work after turning on; immunity of human ears to ultrasound of used frequency.

Disadvantages of ultrasonic system are: dependence of the speed of ultrasonic waves spreading midair on the change of ambient temperature; large enough deadband (25cm), taking into account 1×0.5 m size of measuring base.

Coordinate recording of test results gives an opportunity to provide monitoring of constructions, watching the increasing of material structure defects to form more exact prognosis on accident-free exploitation of construction’s elements. Application of automatic coordinate registration will take off the problem of testing subjectivity.

 

REFERENCES

1) Albert S. Birks. Nondestructive Testing Handbook. Second, ASNDT 1991, Edition. Vol. 7., P. 451.

2) Edward R.S., Jian X., and Dixon S. Signal enhancement of the in- and out-of-plane Rayleigh wave components. Appl. Phys. Lett. 87 (2005), p. 194.

3) Fortunko C.M. and Schramm R.E. An analysis of electromagnetic acoustic transducer arrays for nondestructive evaluation of thick metal sections and weldments.  Rev. Prog. Quant. NDE 2A (2003), pp. 283–307.

4) Shapoorabadi R.J., Sinclair A.N., and Konrad A. Finite element determination of the absolute magnitude of an ultrasonic pulse produced by an EMAT. In 2000 IEEE International Ultrasonics Symposium, Puerto Rico, October (2000).

5) Soua S., Raude A., and Gan T-H. Guided wave in engineering structures using non-contact electromagnetic acoustic transducers – A numerical approach for the technique optimization. Excerpt from the Proceedings of the COMSOL Conference 2009, Milan.

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