Invasive and non-invasive ultrasonic sensor with continuous and demand self-test

摘要

An ultrasonic sensor of either the invasive or non-invasive type having a piezoelectric element for transmitting and receiving ultrasonic energy bonded by an adhesive to the inner face of the wall of a support. When operated in an energy transmitting mode, the energy transmitted by the element is reflected from the interface of the outer face of the wall medium confronting it back to the element. The distance from the front face of the element through the bonding adhesive to the interface is known and when the sensor is in a receiving mode the time of arrival of the reflected signal can be predicted. The received energy is used as a self-test signal to check element dis-bonding. In one embodiment sensor integrity is checked by a digital signal processing technique with the received signal reflected from the interface being periodically sampled and converted into a series of digital numbers. The digital numbers are processed by a cross-correlation technique with a signature signal corresponding to a properly operating sensor. If the element is dis- bonded there will either be no signal reflected from the interface or the reflected signal will not produce the proper series of number corresponding to a properly operating sensor. Detection of a dis- bonded element is accomplished for conditions of the gap being either wet or dry.