Abstract:

In order to ensure the measuring accuracy of resistance type sensor,a gas detecting system based on constant current circuit has been designed.The system uses constant current to make the gas sensor’s resistance  linear  with output voltage,so that the detecting  resistance accuracy  of gas sensor is improved.The  constant current circuit consists of reference voltage supply,current negative feedback circuit,voltage stabilizing diode,and load resistance.After calibration,its measuring range is 0～1 000 kΩ,andcorresponding average measuring error is less than 0.027 2%.By using SnO₂ sensor to detect 0～2 05357  mg/m³ ethanol gas,the calibration results show that the resistance decreases exponentially as the concentration increases,and the maximum detection error is less than ±1.5%.

Key words: gas sensor, SnO₂ sensor, measurement error