With ultrasonic sensors objects of various sizes, surface and color can be detected. An important application is, therefore, the counting of objects. For example, in production facilities. Two basic principles are used:

  • Ultrasonic proximity switch (proximity mode)
  • Ultrasonic through beam sensor (through beam mode)

The proximity sensor emits ultrasound signals and receives it again in the same place. Only one sensor is therefore required. The portion which is reflected by the target is very much smaller than the originally emitted signal. In extreme cases, when the object is small and sound absorbing, the received signal can be many thousand times smaller. It therefore needs sensors at high power and high receiver sensitivity. Advantages of the proximity switch are: only one sensor is needed, the object can be detected from one side. Disadvantages: since the switch is relatively slow and has a wide detection beam, only objects that come along in a relatively large mutual distance can be detected individually.


The through beam sensor consists of two sensors: a transmitter and a receiver. The receiver evaluates the ultrasonic signal emitted by the transmitter. Depending on whether an object is between transmitter and receiver, the received signal is greater or smaller. The advantages of the through beam method are the disadvantages of the proximity sensor: thanks to the narrow detection beam and the high speed the through beam can detect fast moving objects and objects with small mutual distance.


Example: detection or counting of bottles

proximity switche.g. Type UPX or UPS through beamType UPB