A Research On Temperature Control Circuit Of Integrated Gas Detector

In recent years, the environmental problem is drawing more and more attention. In the field of environmental monitoring and interior decoration, the measure of concentrating volatile organic gas is becoming particularly important. The appliance of surface acoustic wave(SAW) coupled with gas chromatography is a kind of fast and sensitive gas detector. To improve the sensitivity and ultimate limit of detection system, it demands strictly temperature controlling.It needs large volume and high power for the heating system of traditional Chromatograph. It is not conducive to the miniaturization of the whole detection system. A scheme of portable temperature controlling device is researched in this paper. The device is controlled under the condition of Constant temperature and programmed temperature. The host computer software is written. It’s able to communicate with the temperature system on the PC.This article is divided into the following three parts:The first part is the temperature control circuit of gas detection design based on PIC MCU. It includes TEC constant temperature circuit, pulse heating circuit for concentrator and temperature reading module. The devices are controlled through the software program of single-chip timer module. The error of frequency is less than 0.004%.The second part is the design of communication module based on Modbus protocol. RS-485 interface conversion circuit is completed. PC software is programmed, with reset / start function.The final part is the temperature control test based on pulse heating, SAW gas room constant temperature control and fast chromatographic separation system. Pulse heating of the concentrator can be heated up to 170℃ in 1.6 seconds. The temperature curve is stable and smooth. The temperature control accuracy is greater than 0.1℃.In the process the heating rate can be up to 50℃/min. The average error is less than 1℃.In the optimized heating condition, the carbon disulfide, methyl mercaptan, dimethyl sulfide, and two methyl two sulfide are separated. And each of the two groups separated time spaced apart more than 30 s.The experimental data shows that the temperature control system can complete the temperature control of each module. It establishes the foundation for the miniaturization of integrated gas detector.