Modeling, simulation and temperature compensation of porous polysilicon capacitive humidity sensor using ANN technique

The porous polysilicon capacitive sensor used for measuring relative humidity has the advantages of low cost, ease of fabrication and CMOS compatibility. However, the capacitance of the sensor, which is a function of concentration of water vapour, also depends on ambient temperature. Thus, variation of ambient temperature causes error in the performance of sensor outputs. In this paper, two ANN models have been developed. The first model is used to simulate the behavior of the capacitive humidity sensor (CHS). This model can also be used for on line monitoring of the fault of the sensor. The second model is based on inverse modeling, which can be used to compensate the effect of ambient temperature error. It is found from the simulation studies that the error of the direct model is within +/-2% of full scale and for the inverse model the error is within +/-0.5% of full scale over a temperature range from 20 to 70degreesC. A hardware implementation scheme for realization of the CHS model is also proposed. (C) 2004 Elsevier Ltd. All rights reserved.