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Development of an Intelligent, Digitized High-speed, On-line Eddy Current Inspection Equipment Lin Junming, Lin Chunming, Lin Fabing ( Eddysun (Xiamen) Electronic Co., Ltd.) Chen Kaihui (Guangdong Nuclear Power Joint Venture Co. Ltd.) Contact

Abstract:

This paper introduces the on-site application of fully digitized eddy current equipment with high variable inspection speed. The characteristics of the equipment allows metal tubes, bars and wires pass through the eddy current probe with high variable speed, and therefore the position of the defects can be accurately measured, marked and recorded. The highest speed of the inspection is 350M/min. It possesses itself of higher economic value for the application in industries.
Keywords: Intelligent eddy-current, the inspection of high-speed, on-line, adaptive ability

1. Introduction

During the manufacturing process of many metal tubes, bars and wires, they pass through the transducers always with variable speed. At the first some specific requirements will be put forth against the eddy current equipment by this variable speed, i.e. adaptive ability of the eddy current equipment will be strengthened largely. Secondly, after the passing speed of the material being examined reaches to certain content, it is difficult to design accurately recording and marking position system. For example, in the in-service inspection of a wound copper tube machining when its production rate varies from 0~350m/min, the general eddy current equipment can not meet the inspection requirement of this production process. Therefore fully digitized eddy current inspection equipment with high variable inspection speed has been developed to meet this requirement. EEC-24, an intelligent, fully digitized, and highly inspection speed eddy current equipment, is briefly explained in this paper.

2. EEC-24 equipment

The block circuit of EEC-24 system is shown in Fig. 1 and it consists of three parts: highly speed adaptive eddy current detection circuit, speed position measuring circuit and marking control circuit Fig1

Fig 1:

2.1 Eddy current detection circuit
The principle block circuit of the eddy current detection is shown in Fig. 2A and 2B. The response of its amplifier to eddy current signals shall be fast enough and the amplifier has frequency response of a wide range, so that it can follow up the eddy current signal changes when the material being detected is passing through with high speed and is shown in Fig.3. Moreover in order to improve the signal noise ratio, a synchronous following up filter and a gain compensation controller are designed specially to adapt itself to requirements for the condition of variable speed. A switch capacitor circuit is adopted in synchronous filter, and a variable gain operation amplifier is selected for gain compensation. It is also shown in Fig 3.

Fig 2A:

Fig 2B:

2.2 Speed measuring circuit
An optical electronic coding is used to provide length, marking defects, and defect position measurements with information signals, so that the equipment parameters can be adapted in time correspondingly.

2.3 Marking controller
For tube inspection, the function of the marking controller is that when a defect on the tube being measured moves to corresponding position of marking controller, the eddy current signal induced by the defect triggers the marking controller and then the marking controller marks the defect position.

Fig 3:

Fig 4:

Since a certain distance between eddy current detection transducer and marking controller, the marking signal of the equipment has to be delayed correspondingly to trigger the marking controller and marks the detected defect. Set the time of the recently detected defect as t₁, and so the time of triggering the marking controller t₂ is determined by the following formula (see Fig. 4)

t=Vdt...........................(1)

Where, v is moving speed of the material being detected. In addition, when a marking signal does not reach the marking controller yet, it is possible that a new defect appears on the tube section being detected. Therefore, the marking controller shall posses itself of ability to retain and arrange multiple defects in it. The marking controller of the equipment can memorize 512 defect signals, i. e. in Fig .4, if 512 defects appear in 1 area, they will be marked accurately and reliably and then the area can be judged for cutting processing.

3. Specification of the EEC-24

EEC-24 is an intelligent, fully digitized, and highly inspection speed eddy current equipment and its main technical specifications are as follows:
• Maximum detection speed:     350m/min
• Frequency: range:    60Hz~4MHz
• Gain range:    0dB~90dB, step 0.5dB
• Automatically record and display defect number and its position
• The inspection reports (including detecting length, total defects number and the position of each defect) will be automatically formed
• Wide band digital filter which can reduce disturbing signals for variable on-line detection speed
• The driving current of the eddy current transducer is adjustable
• The phase rotation of the eddy current signal can be adjusted 0~359°with accuracy 1°. In the process of phase setting, new amplitude and phase angle of the eddy current signal being analyzed can be promptly displayed on their impedance plane. The setting of initial phase angle is simple and directly perceived.
• Fast digital/analogue electronic balance
• Single trace impedance plane as well two internal strips for rolling display of eddy current signals
• Single A-scan display or double A-scan displays
• Memorizing tracing delay and hidden-line elimination
• Interactive menu (Chinese version with popular/old font or English version), keyboard operation with hot key help
• The amplitude and phase angle of the eddy current signals can be automatically measured, and eddy current signals redisplayed with time expansion for detail data analysis
• Adjustable sampling rate
• Absolute, differential, or self-comparison eddy current probes can be used (including passing through, internally insetting, plane, pointer, and rotating probes)
• Non equal amplitude phase/amplitude alarm threshold in original creation
• 8 hardware alarm output ports
• Huge hard disk for storage of various inspection programs, data and figures
• Cartesian or polar coordinates with their different background can be selected

4. Conclusion

Module circuitss and integrative structure designs are adopted in EEC-24 and in it all controls can be carried out by one computer. In comparison with the functions of the other same product, it is more complete and compact in structure. At the present, the equipment has been applied to many industrial sectors and good results have been achieved.

References

1. Chen Kaihui etc, "The Eddy Current Inspection of Titanium Tubes of The Condensers in Guangdong Nuclear Power plant", Non Destructive Testing, March 1995.
2. Lin junming, "Improvement on On-line Eddy Current Equipment for Steel Tubes Inspection", Non Destructive Detection, 1 (1992) p35-39
3. Lue Zhongli, "The Prospects of Non Destructive Testing Techniques in Boiler Pipes of Fossil Power Plants", Proceedings of 6^th NDT Technical Conference in Power System
4. Lin Juming, Lin Chunjing "Intelligent, Fully Digitized Spectrum Analyzer for Eddy Current Inspection", Non Destructive Testing, June,1993
5. Lin Junming, "The Newest Technique of Eddy Current Detection Instruments for Modern Steel Tube", Welded Pipe and Tube, 6 (1994) p32-34

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