Design Of A Photoionization Detector For VOC Gas Detection

Photoionization Detector(PID)is a sensor that can be used to detect low concentration of Volatile Organic Compounds(VOC).High concentration of VOC gas is harmful to human's production and life,and is fatal and explosive.Due to its features of non-destructive measurement and good safety,the Photoionization Detector has a wider range of applications than other types of VOC gas detection sensors.In addition to its widespread use in medical,environmental monitoring and industrial inspection,it has also been used in the anti-terrorism military field in recent years to detect poison gas.Due to the increasing application of Photoionization Detector,Photoionization Detector are becoming more and more important in VOC gas detection.Based on the research on the development and existing problems of commercial Photoionization Detector and the existing Photoionization Detector's design technology,a new Photoionization Detector is designed to solve the problems of current Photoionization Detector and optimize the performance of Photoionization Detector.The sensor uses the German Heraeus PKR 106-6-14 UV lamp as the ultraviolet light source,and the photon energy output by the UV lamp is 10.6 e V.A push-pull amplifier circuit is built using a 555 timer,a transformer,and three triodes as a driving power source for the ultraviolet lamp.PTFE is selected as the material to design sensor parts,Axial structure is used as the structure of the ionization chamber and stainless steel is used to design bias electrodes and measuring electrode in ionization chamber.XC9103 and TPS40210 are used to complete DC power supply design,the output voltage is 300 V and it is added to the bias electrodes to create a electric field for collecting ions.According to the size of the ultraviolet lamp and the size of the electrodes,the structural design and overall modeling of the ionization chamber and other parts and the fluid simulation are completed.The signal detection processing part of the sensor uses the ADA4530-1,OPA2735,and ADS1115 to complete the design of the I/V conversion and amplification circuit,the filter circuit,and the A/D conversion circuit.In order to ensure good linearity and the stability of the measured voltage value of the sensor,a metal shield layer and the chassis ground are added to prevent the influence of power frequency noise on the sensor signal.The DC power supply of the signal detection processing part is completed by the XC6201,and the output voltage of this circuit is 3.3V.Isobutylene gas with standard concentrations of 0.5ppm and 1ppm,mixed gas of nitrogen and oxygen to represent pure air are used as test gas to verify the sensor prototype by experiments.The experimental results show that the sensor can accurately measure volatile organic compounds with concentrations as low as 1 ppb,with an accuracy of 10%,fast response,good consistency,linearity,repeatability and stability.