Ultrasonic detection device, notably for an automatically controlled windscreen cleaning system

Ultrasonic detection device for detecting the presence of foreign bodies such as water on a window, comprising:

• transducer means (10) for emitting a sequence of ultrasonic pulses (31) propogating within the thickness of said window (1) and receiving a series of reflected pulses (32) resulting from each said ultrasonic pulse, the reflected pulses in each said series having an amplitude which decreases in time at a rate which varies as a function of the presence of said foreign bodies (33) on said window, said transducer means (10) producing an echo signal (40,50) representative of each said series of reflected pulses,
• characterised in that it further comprises:
• amplifier means (23) for amplifying said echo signals (40,50) by a selectable gain,
• integration means (26) for integrating each said echo signal (40,50) during a selected time period (62,63) so as to produce an integral value,
• amplifier control means (27,28) for measuring said integral value and selecting said gain so as to maintain said integral value at a steady-state value, and
• means (29) for measuring the temporal deviation of said integral value from said steady-state value and determining if said temporal deviation is greater than a predetermined threshold value.