Foundational Research Of PID Gas Sensor

Photo Ionization Detector (called PID) is a sensor with high sensitivity and a far-ranging application. It can detect volatile organic compounds (called VOC) and other poisonous gas from very low density of 1ppb to high density of 10000ppm (1%). Compared with traditional detective methods, it has the advantage of portable type, high accuracy (ppm magnitude), fast response and continuous test and so on. It can provide real-time information feedback to staff and they can confirm that they are not exposed to the dangerous chemicals, so we can protect the detection staff better. Currently optical ionization sensor has been widely used in various organic chemical detections, particularly play an important role in leak detection in disaster area's accident and confirming the accident district and the leaking section.This paper introduces the foundamental knowledge of gas detection by ultraviolet, completes the systemic design of ultraviolet gas snsor based on the PID principle. The gas sensor is tested by the calibration experiment, and results are good. The system design of gas sensor, the dirving circuit of ultraviolet lamp, the gas signal detection, the design of ionization chamber, the signal processing circuit are illuminated in the paper.The photo ionization mechanism is present in the thesis. The concentration of the measured gas has linear relation with the optical ionization current and could be used as the gas detecting, when the optical length of sample pool is short enough and the concentration of the sample is low enough. Through the investigation, the ionization chamber is designed, which has quick-response, high gas tightness, and stabilable signal. The driving mechanism of special ultraviolet lamp for gas detecting, which could real-time adjust the power of the ultraviolet lamp, and this is very important for the consistency of the gas sensor. And the driving circuit which could produce the double channels of 100K, 1500V alternating current is designed through the EWB simulation. According to the character of output signal, the weak signal detecting circuit of the gas sensor is designed. And the circuit completed the function of the abstract and amplification of the signal, arid the analog filter circuit is designed to fullfil the function of primary filter of the signal. This paper focused on the integrated design of the detection system, the weak signal detection and the software and hardware design of the detection system, and how to complete the fuctions, such as data-collection, processing identification, digital filter et al. The design of the circumferential facilities, such as the driving circuit of the fan and current source, are presented in the paper.The die of shell is designed based on the National Standard for Explosion Protection, and the relevant design about explosion protection, waterproof, dust prevention, radiation protection. After completing the system integration of the prototype machine, the calibrating test is carried on, and the result is good.This paper introduces an optical ion gas sensor, and break through the manufacturing methods of the traditional optical ionization detector, and the design and the processing of the ionization chamber are considerably simple. The volume and the mass of the sensor will be reduced greatly, and the high price and cost of the optical ion sensor are also reduced. It is a very important step for promoting its market process.