Patent ID: 8421046

Claim:
A method for keeping clean a sensor window of an optical sensor for detecting value documents and/or at least one property of value documents which is disposed with at least one portion in a beam path of the sensor, comprising the steps: generating a moving gas film on the at least one portion of the sensor window so that the gas film is attached to a surface of the at least one portion by the gas moving in a direction relative to the at least one portion; and blowing the gas out from at least one blowing nozzle at an angle in the range between 15° and 35° with respect to a plane parallel to the at least one portion of the sensor window, wherein a stream of gas formed by the blown out gas from an opening of the at least one blowing nozzle moving parallel to the flow direction on the at least one portion and in a plane parallel to the flow direction of the gas in the gas film on the at least one portion has a width in the range between 0.1 mm and 0.2 mm.