Patent ID: 8652552

Claim:
An apparatus for estimating the air humidity within an oven cavity ( 14 ) by using ultrasound waves with at least two different frequencies (f 1 , f 2 ), wherein said apparatus comprises: at least one ultrasound transmitter ( 10 ) for generating the ultrasound waves, at least one ultrasound receiver ( 12 ) for receiving the ultrasound waves, at least one phase detecting device for detecting the phase (φ 1, φ 2 ) of the ultrasound wave at the ultrasound receiver ( 12 ) relative to the same ultrasound wave with the same frequency (f 1 , f 2 ), at the ultrasound transmitter ( 10 ), at least one evaluation unit for calculating the velocity (V) of the ultrasound waves on the basis of the phases (φ 1, φ 2 ) and frequencies (f 1 , f 2 ), of the ultrasound waves with the two different frequencies (f 1 , f 2 ), at least one temperature sensor ( 32 ) for detecting the temperature (T) in the oven cavity ( 14 ), and at least one estimation unit for estimating the humidity in the oven cavity ( 14 ) on the basis of the temperature (T) in the oven cavity ( 14 ) and the velocity (V) of the ultrasound waves.