摘要 |
A time gate ultrasonic sensor (10) measures a physical property of a material, such as the presence of the material, within a defined space (20). The sensor (10) includes at least one transducer (14, 16) connected to a support structure (12) and positioned generally adjacent the defined space (20) for transmitting and receiving ultrasonic signals (22) across the defined space (20). The ultrasonic signals (22) include a main waveform (48, 62) which travels across the defined space (20) and a self-test waveform (50, 60) which travels along the support structure (18, 43). The sensor (10) monitors the received ultrasonic signals (22) during a main time window (120) to sense whether the main waveform (48, 62) is present in the received signals (22). The sensor (10) senses the physical property of the material within the defined space (20) as a function of whether the main waveform (48, 62) is present within the time window (120). |