Design of Precision Measurement Circuits for the Relative Humidity

摘要

The two methods of the relative humidity measurement are introduced in this paper. The one is adopting transistor and operational amplifier to compose a logarithmic amplifier, by which to realize the linearization of exponent mode character curve of moisture-sensitive resistor. And using the positive temperature coefficient of the adjustable currentsource ( + 0.33%/°C) compensate the negative temperature coefficient of the thermistor ( - 0.36%/°C ) . Zerotemperature drift is realized by the methods and the measurement accuracy reached ±2%. The two is adopting intelligenttemperature/relative humidity sensor, which combined the multiple parameter sensor and transmitter, to realize the accurately measurement not only of the relative humidity, but also of the temperature and dew point. Through the 2-wires serial port the system can be connected to MCS-51 MCU. The accuracy of the relative humidity measurement is ± 1.8%; the nonlinear error can be reduced to ±0.1% after software arithmetic compensation. The temperature range measured is -40～ + 123.8°C. The accuracy of dew point measurement is <±1°C.