Development Of AC Bridge Eddy Current Testing System Based On Impedance Analytical Method

With the development of science and technology, the requirement on measurement technology is getting more and more important. The application of electronic measurement technique has extended to more fields than ever. Due to limited functions and bulky, traditional electronic measurement equipment is very difficult to meet demands of real work. Thanks to the rapid development of integrated circuit and computer technology, measurement instruments are becoming digitized and intelligentized. Compared with traditional equipment, the new instruments have more functions, higher processing speed, wider bandwidth, friendlier interface, smaller size and better expandability. The prevalence and rocketing development of personal computers give birth to a new kind of instrument, Virtual Instrument (VI).VI is based on PC platform, which makes it convenient to use the software and hardware resources of PC and lets the ability of data processing flexible. With VI, a measure system can be easily built for different requirements of measurement. In order to meet the demand of eddy current In-System testing and imaging testing, a new eddy current testing system was developed based on LabVIEW. The system was composed of hardware circuit, computer, data acquisition card and relative software.The hardware circuit included excitation source, AC bridge, preamplifier, auto-balance circuit, adjustable amplification, phase-sensitive detection and Filtering modules. Direct Digital Synthesis (DDS) technology was used in the design of the excitation source. The auto-balance module could be set by users to achieve rapid automatic balance, and will greatly enhanced the system's capacity of detecting a weak signal. The total gain of the circuit could be 86dB.PCI9812 data acquisition card was used for the signal data acquisition. LabVIEW virtual instrument software platform was used to develop the software system. The system displayed two time-based strip charts and presented the phase and amplitude vectors of the eddy current signal as a two-dimensional Lissajous figure. Eddy current transducers were developed. Testing experiments were done through the system, and the results showed that the system had good testing capability, high stability and repeat-ability.