| 摘要 |
PURPOSE:To prevent the change in the characteristics of a moisture sensing resistor with the contamination of said resistor, by heating a resistance heating element at a specified period to 300 deg.C or above, keeping the same at said temp. to assure the time necessary for combustion of the dust and oils sticking on the moisture sensing resistor, measuring the resistance value of said resistor when the resistor attains about the same temp. as the ambient temp. and detecting the humidity. CONSTITUTION:A control signal A is applied from a control circuit 12 to a switch circuit 4 and a delay circuit 13. When the signal A is in an H state, the transistor 5 of the circuit 4 turns on and electricity is supplied from a power source 3 to a resistance heating element 1. The element 1 generates heat by which a moisture sensing resistor 2 is heated to the temp. TH higher than 300 deg.C, and the contaminants sticking on the surface of the resistor 2 and the contaminants suspending in the atmosphere around the same are burned away. Then the TR5 of the circuit 4 turns off, and the supply of electricity to the element 1 is interrupted. The resistor 2 is allowed to cool of itself down to the room temp. TL, thus indicating the resistance value corresponding to the relative humidity of the ambient atmosphere. The resistance value is measured and the humidity is detected. |
