Abstract: A method of monitoring a sequence of documents passing along a transport path is described. The method including: operating a radiation transmitter with a control signal at a first, working, level to cause radiation at a first intensity to impinge on one side of a document as it passes an inspection position in the transport path; receiving at a radiation receiver, radiation from the transmitter that has passed through the document, the radiation receiver generating an output signal with a level related to the intensity of the received radiation; and monitoring the output signal to detect the presence and/or a characteristic of the document.

Abstract: Document inspection system comprising a transport system for transporting documents along a transport path (12) through an inspection station. At least one ultrasonic inspection apparatus at the inspection station, the apparatus including ultrasonic transmitting and receiving transducers (42,44) arranged on opposite sides of the transport path, and a processing system for monitoring ultrasonic signals received by the receiving transducer. An ultrasonic absorbing material (300) is provided around the transducers and facing the transport path for absorbing ultrasound reflected by a document. Document guide apparatus (312,314), having a lower coefficient of friction than the absorbing material, extends partially over the absorbing material (300) so as to prevent documents contacting the absorbing material in use while leaving the absorbing material exposed to the transport path at least adjacent the transducers.

Abstract: A method of monitoring a sequence of documents passing along a transport path is described. The method including: operating a radiation transmitter with a control signal at a first, working, level to cause radiation at a first intensity to impinge on one side of a document as it passes an inspection position in the transport path; receiving at a radiation receiver, radiation from the transmitter that has passed through the document, the radiation receiver generating an output signal with a level related to the intensity of the received radiation; and monitoring the output signal to detect the presence and/or a characteristic of the document.

Abstract: Document inspection system comprising a transport system for transporting documents along a transport path (12) through an inspection station. At least one ultrasonic inspection apparatus at the inspection station, the apparatus including ultrasonic transmitting and receiving transducers (42,44) arranged on opposite sides of the transport path, and a processing system for monitoring ultrasonic signals received by the receiving transducer. An ultrasonic absorbing material (300) is provided around the transducers and facing the transport path for absorbing Document guide apparatus (312,314), having a lower coefficient of friction than the absorbing material, extends partially over the absorbing material (300) so as to prevent documents contacting the absorbing material in use while leaving the absorbing material exposed to the transport path at least adjacent the transducers.