Patent ID: 8178044

Claim:
A liquid property detecting device comprising: an electrode portion that defines a first capacitor having liquid as a dielectric material; and a circuit portion that calculates a concentration of the liquid, the circuit portion including: a generator to generate standard voltage applied to the electrode; a switch portion to switch the electrode to charge with the standard voltage or discharge through a grounding; an operation signal output portion to output a first operation signal having a first frequency to the switch portion so as to perform the switching in a first switch period, or a second operation signal having a second frequency to the switch portion so as to perform the switching in a second switch period; and a signal process portion to process a detection signal corresponding to a voltage of the electrode when the standard voltage is applied to the electrode, wherein the signal process portion calculates liquid property based on a first detection signal corresponding to the detection signal when the switch portion performs the switching in the first switch period, and a second detection signal corresponding to the detection signal when the switch portion performs the switching in the second switch period, the signal process portion has a gain relative to the detection signal in the calculation of the liquid property, the signal process portion changes the gain in accordance with at least one of the first detection signal and the second detection signal, the gain is configured to be increased as at least one of the first detection signal and the second detection signal is decreased, and the circuit portion calculates the concentration of the liquid based on the first detection signal and the second detection signal as the liquid property.