2.1 Measuring Distance with an Ultrasonic Transceiver

In this application note, an ultrasonic transceiver is used to measure the distance to a barrier, calculated from the "time of flight" between a transmitted ultrasonic burst and receiving its reflection. This process can also be referred to as "echo ranging". The first figure below illustrates the principle. The burst produced by the transceiver bounces off the barrier object and returns to be received after a time interval. The variation in distance traveled is proportional to the measured time interval, related by a factor of the speed of sound.

Figure 2-1. Ultrasonic Distance Measurement Principle

The signals transmitted and received by an ultrasonic transducer can be visually inspected via an oscilloscope. An example is depicted in the figure below. The dotted orange lines indicate the measurable "time of flight" mentioned above. It can be seen that the reflected wave is significantly attenuated; this should be kept in mind during application design in order to detect the received signal as soon as possible.

Figure 2-2. Ultrasonic Transducer "Time of Flight" Oscilloscope Screen Capture