US Patent 7117739 Fluid-gauging probes

An ultrasonic fluid-gauging probe has a still well and two or more piezoelectric transducer elements mounted at its lower end. A drive and processor unit may separately energize each element and provide a separate output indicative of fluid height so as to provide redundancy. Alternatively, one element may be energized and the other used to receive the reflected signal in normal use but, when a fault is detected, one element may be used to both transmit and receive. The elements may be mounted side-by-side, such as on a common substrate, or one above the other in a stack.