Fast humidity sensor using optoelectronic detection on pulsed Peltier device

Abstract In order to develop a new way to use a Peltier device in a fast humidity sensor, we have studied the optical signal of a photodetector when water condensation appears on the cold side of a commercial Peltier module. The thermoelectric device is used at pulsed rate. During the cooling the applied current is stopped as soon as a variation of the optical response, due to the appearance of water droplets, is observed. A reverse pulse is then applied to return quickly to the ambient temperature. We have measured the response time of a small commercial Peltier module. The experimental thermal time constant τ th measured during the cooling using a thermocouple is typically τ th = 3.6 s. A calculated estimation of the reverse pulse time is given in order to optimize the return to the equilibrium room temperature for low relative humidity. The last part of this work is devoted to measurements of the relative humidity H R . The delay time T C of the optical detection is plotted as a function of humidity level. T C is function of the Peltier current supply I peltier : with I peltier equal to 700 mA, we have observed a delay time T C in the range 0.25 s ≤ T C ≤ 12.2 s for 15% ≤ H R ≤ 70%.