Abstract: Non-methane total hydrocarbon (NMHC) has long been a class of the most harmful air pollutants, which are often monitored using NMHC analyzer. The working principle of NMHC analyzer determines its high requirements for response speed and control precision to the gas flow. In order to meet the requirements of NMHC analyzer and the instantaneous characteristics of actual gas flow, a high precision gas pressure control algorithm is proposed in this work taking the position PID algorithm as a base and the fuzzy control algorithm as an auxiliary adjustment means. The algorithm can achieve high precision control of gas flow by adjusting the gas pressure, and different experiments are designed to verify the performance of the algorithm. Experimental results show that compared with traditional PID algorithms, the proposed fuzzy control PID algorithm has faster response speed, smaller overshoot and higher regulation precision. It can calculate the opening and closing size of proportional valve according to the error between the set value and the actual value of pressure control, thus achieving the design goal of efficient control of gas flow and realizing the accurate measurement of NMHC concentration in air pollution areas. By using this control algorithm, the error of each gas control pressure can be controlled within ±0.1 kpa. The proposed algorithm has high stability and simple implementation, and is easy to be applied to embedded systems. It provides a reference for the application of NMHC analyzer in environmental monitoring.

Key words: non-methane total hydrocarbon, PID algorithm, gas pressure control, fuzzy control