Patent ID: 7719290

Claim:
A circuit configuration for measuring air humidity, comprising: a measurement system including an oscillator unit and a signal-processor unit, the oscillator unit including an oscillator and a switchable impedance; and a frequency-determining impedance including a capacitive humidity sensor and a parasitic resistance connected in parallel, the frequency-determining impedance connected to the oscillator unit; wherein an oscillation frequency of the oscillator is a function of (a) the frequency-determining impedance and (b) a falsifying influence of the parasitic resistance, the oscillator switchable from a first frequency range to a second frequency range by connection of the switchable impedance to the frequency-determining impedance; wherein the oscillator unit is configured to supply an oscillator signal having the oscillation frequency of the oscillator to the signal-processor unit, the signal-processor unit configured to measure the frequency of the oscillator signal and to ascertain a correction value to compensate for influence of the parasitic resistance on the oscillation frequency as a function of a difference between a first measurement of the frequency of the oscillator signal in the first frequency range and a second measurement of the frequency of the oscillator signal in the second frequency range; wherein the influence of the parasitic resistance on the oscillation frequency of the oscillator is different in the first frequency range and the second frequency range; and wherein the signal-processor unit is adapted to determine a corrected frequency of the oscillator signal and to ascertain a corrected humidity value from the corrected frequency of the oscillator signal that does not include a measurement error caused by the parasitic resistance.