The Research And Implementation Of Portable Photoionization Detector

Photoionzation Detector(PID) is a sensor referred by Photoionzation technology which be used to detecet specific Volatile Organic Compounds concentrartions that,as a kind of high sensitivity ,extensive use detector. The detector's principle of work is that,when the subject measured be irradiated by the UV lamp which have high energy than the subject's, the subject will be ionized into charged ions.,the charged ions will to be current under the action of applied electric field, we will measure the concentrations of the subject measured by measuring the size of the current, as a result, we can tell people whether the subject is harmful for the purpose of protecting hurman being. In view of miniaturization of modern Gas Chromatography development,also to the protable detector.More and more people are in favor of Photoionzation Detector due to its own advantage.Firstly,being elaborated the results for theory of Photoionzation technology, studied the knowledge of weak signal detection and de-noising, and with our research of development in this field, we put forward our own design proposal. Including the UV lamp selection, the ionization chamber design, I-V converting circuit, AD sampling and single-chip microcomputer control circuit,UV lamp drivers citcuit and ionization chamber polarization power circuit,the ARM signal processing and control system.First this paper analyzes the related theory of photoionzation ,only when the optical path is short enough , the sample concentration is low enough , the relation between the concentration of the measued and the current produced proformance a linear relation. Then we analyzed the influence about the sensitive head–to-follow-up circuit,and studied the drive mode of UV lamp, finally we decided to adopt PKR106-6 UV lamp which will be excited by RF produced by Heraeu company. Considering the UV lamp and analyzed the influence factors of the test result ,we put forward and designed a fast response,good gas tightness, adequate reaction structure of chamber, and also designed the relevant drive circuit around the sensitive head.The current signal came from sensitive head entered the I-V converting circuit designed by us and whose core component is AD549 for I-V conversion and amplification , after the conversion of voltage signal can be amplified by 10 8,10 9, we made repeated test for the I-V circuit to verify its output achieved good effect .After conversion and amplification,the voltage signal entered the sampling circuit,this circuit that single-chip microcomputer control AD7718 do sampling will made analog signal into digital signal.After sampling the signal entered processing system to be processed, in this design we use double CPU communication system to process signal,the signal came from SCM gone into dual-port RAM(IDT7005S),the dual-port RAM connected to ARM9 by the ISA bus,the ARM9 do some necessary signal processing,and after processing the signal will be give PC to show by Ethernet.After the hardware completed,we we had repeated the experiments to verify the system output reached design standards.