Research On Characteristics Of Amplification And Conversion For Photocurrent Signal Of Detector In Industrial CT

With the development and wide application of industrial CT , the size of the detected object becomes wider and wider , the speed of testing becomes faster and faster, the precision of detection becomes higher and higher, which leads to increasingly demanding for performance of industrial CT systems. CT radiation detection system as the key subsystem of industrial CT, its performance also should be increased. Scintillator photodiode detector is most commonly used as an industrial CT detector, it is necessary to analysis the characteristics of the optical current signal and study the way of treatment. In particular, it is very important that researching on characteristics of amplification and conversion for photocurrent signal of detector in Industrial CT , because which is beneficial to improve the speed of acquisition, the accuracy of detection and the dynamic range of detection, so that to improve the performance of industrial CT systems.This paper first describes the structure and working principle of industrial CT system,the effect of detection system to the performance of industrial CT, the development of industrial CT detection system and the significance of this subject, then defined the effect of this research to the industrial CT system. Secondly, through the in-depth analysis to detection system, this paper proposes a method processing for output signal of scintillation detector and sets a platform used for researching on amplification and conversion characteristics of photocurrent signal, this platform integrates pre-amplifier, secondary amplification, differential conversion, AD converter and the FPGA control circuit. The designs and hardware implementations of various parts are described in this paper.Based on this platform, this paper mainly completes the research on I-V conversion of photocurrent signal, including the influences of integration capacitor and integtation time to output voltage, analyzes how to select integration capacitor in order to reduce integration time, proposes a solution that using air-parallel plate capacitor and 0.1pF thin film capacitor as integral capacitor, and through establishing a weak signal circuit to generate 5nA current as the system input, tests the result of the application for these two options based on the platform. Apart from this, this paper also makes some researchs on secondary voltage amplification and AD conversion characteristics, in order to know how to ensure detection accuracy while increasing the dynamic range of detectors and other issues.