An ultrasonic/optical pulse sensor for precise distance measurements

The combined ultrasonic transit time and optical pulse method described here is an improvement over the standard ultrasonic echo by providing a lower signal loss and more precise location of sensor reference points, specifically the transmitting and receiving transducers. The ultrasonic transit time sensor described here uses only a one-way ultrasonic pulse. The transit time, typically 0.5 to 50 ms, is proportional to the distance between the ultrasonic transmitter and receiver transducers. There are three advantages: (1) the ultrasonic signal loss is much less, (2) the location of the transducers is well defined, and (3) the phase and pulse shapes are controlled and reproducible. An optical pulse is used to synchronize the transmitter and receiver. In this version the optical pulse is sent from the ultrasonic receiver unit, initiated by its microcontroller, to the ultrasonic transmitter unit.