HP-15 humidity meter circuit

This hygrometer uses a finished humidity sensor HP-15P to convert humidity into voltage . It drives a pointer voltmeter.
The characteristics of the humidity sensor HP-15 are as follows: humidity range 10%RH～90%RH; temperature range 0℃-60℃; frequency 50Hz～1kHz; response characteristics (30%RH～90%RH) ≤2 minutes. The following figure is the circuit
of the hygrometer , which consists of five parts. The humidity and voltage conversion part is the HP-15 sensor: the oscillation part provides a 600Hz rectangular wave for the sensor by the time base circuit: the amplifier part is composed of an 11-fold amplifier by the op amp : the output of the amplifier is doubled and rectified; finally, the op amp is connected to a follower for drive output. One of the measurement results: at 30℃ and humidity 45%RH, the output voltage is about 604mV. The humidity sensor resistance is about 90kΩ. 604mV=input signal (5V)÷(90kΩ+1kΩ)×1kΩ×11 times. The output of the driver in the figure can be input to a PIC microcontroller for humidity measurement and display; it can also be input to a humidity controller to use a relay to turn on a humidifier or ventilation fan, etc.

Uploaded on 2011-9-2 18:56:07

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