Ultrasonic Sensors Knowledge (Part 1): Technology and Functionality in a Nutshell

Highly-developed ultrasonic technology builds the foundation for sensing versatility. The underlying principle is the non-contact detection of objects and the measurement of their distance from the ultrasonic sensor. Depending on the type of sensor, these distances can range from a few centimeters up to 10 meters. The sensor emits ultrasonic pulses which are then reflected by an object.

The generated echo is received by the ultrasonic sensor and converted into an electric signal via the piezoelectric transducer. This is known as the propagation time of sound. The sensor measures the time lag between the emitted ultrasonic pulse and the received echo and calculates the distance to the object using the speed of sound. At room temperature, the speed of sound in air is about 344 m/s.

The sensing range of an ultrasonic sensor depends on the surface properties and angle of the object. The longest sensing ranges are achieved with objects that have a flat surface (standard reflector) positioned at an exact right angle to the sensor axis. Very small objects or objects that partially deflect the sound will reduce the sensing range. Objects with smooth surfaces must be positioned as close as possible to an angle of 90°. Rough surfaces are able to tolerate much larger angular deviations.

Environmental effects must also be considered. The biggest influence on the accuracy of an ultrasonic sensor is the air temperature. Pepperl+Fuchs ultrasonic sensors are equipped with compensation circuitry to eliminate temperature effects on the sensor output. Relative humidity and barometric pressure must also be considered.