Research On Temperature Control Technology For SAW Sensor With High Precision And Large Dynamic Range

In the past 30 years,there have been frequent terrorist attacks at home and abroad based on self-made simple bombs such as human bombs and car bombs.These bombs have a greater power and have caused large-scale casualties as a result of explosions in crowded places.People's lives have been seriously threatened.It has caused very bad influence on economic development and social public safety and has become a matter of great concern to governments of all countries.Therefore,there is an urgent need to improve the detection level of explosives and to study the high-sensitivity and fastresponse explosive sensor.In this project,a new type of SAW(Surface Acoustic Wave)gas sensor is used for explosive detection.It is used in conjunction with chromatography to perform qualitative analysis of the gas to be measured,and the separation gas molecules flowing from the end of the column are condensed and adsorbed at low temperatures.SAW device surface,complete quantitative analysis.This is a physical adsorption,which avoids the problems caused by the introduction of sensitive thin films.The condensing SAW gas sensor is much more sensitive than the sensitive membrane SAW gas sensor.According to the working principle of the condensing SAW gas sensor,it can be seen that precise temperature control is a prerequisite for its high-precision measurement.In this paper,the temperature control circuit of the SAW gas sensor for detecting explosives is studied.According to the operating mode of the condensing SAW gas sensor and the nature of the test object,a temperature control requirement is proposed: the temperature is adjusted within a range of 10? to 75?,and the temperature stability at a constant temperature condensation is ±0.02?.The overall scheme of the temperature control circuit adopts a negative feedback type of closed-loop control,including a temperature-controlled actuator,a thermoelectric cooler(TEC),a temperature measurement module,a temperature setting module,and a core temperature control chip.This project uses the temperature control chip MAX1978 to drive the TEC,NTC thermistor temperature measurement module and temperature control chip to achieve high precision temperature control,digital potentiometer ADN2850 and AD8606 operational amplifier temperature setting module to achieve temperature adjustment in the large dynamic range.After SAW gas sensor,TEC,NTC thermistor and SAW oscillation circuit were integrated,the temperature control circuit was tested for performance.The performance test mainly includes temperature adjustment range test and temperature stability test.Temperature control can be achieved in the range of 10?~78?.The temperature stability is less than 0.01? in 10?~30?,the temperature stability in 30°C~50°C does not exceed 0.05?,and the stability in 70? is 0.18?,the worst temperature stability at 78 ? is 0.22 ?.