Functionality and differences of infrared, high-frequency and ultrasonic sensors

In dieser Ausgabe von Marcs Technik Ecke möchte ich Ihnen die Funktionsweise und Unterschiede von Infrarot, Hochfrequenz und Ultraschall Sensor vorstellen.

Basics about motion detectors

A motion detector is an electronic sensor that detects movements in its immediate surroundings and can therefore function as an electrical switch. It is mainly used to switch on a light or trigger an alarm.
A motion detector works either passively using infrared radiation [IR] from the surroundings, actively using electromagnetic waves [HF or Doppler radar] or using ultrasound [ultrasonic motion detector].

IR and HF sensors are mainly used for the common applications of DEKO-LIGHT products.

Infrared sensor (IR)

An infrared sensor [also called a passive infrared sensor] detects the heat emitted from the environment. Detection by the sensor takes place radially in detection areas at an angle of max. 180°, which radiate away from the sensor. The sensor only reports if there are changes in the detection areas. For example, a person approaching the sensor with pinpoint accuracy may not be immediately detected because the person is always in the same detection zone and the sensor therefore does not register any change. If several IR sensors are mounted, they should therefore always be mounted offset.

Wall mounted luminaire Tucanae Motion

Sensor receives in detection range

Module design with IR receiver

High frequency sensor (HF)

While IR uses a passive method, the HF method is based on the principle of radar measurement [most drivers have probably already experienced this detection method in practice]. Radar beams are emitted by a detector, reflected by objects and reported when the distance changes. For this reason, the effect of not being reported by an IR sensor as described above cannot occur with an HF sensor. Detection can be carried out horizontally or vertically and even through a thin layer of glass. Due to their high sensitivity, classic HF sensors are only suitable for indoor areas.

iHF sensors [intelligent high-frequency sensors] are suitable for outdoor use. Thanks to intelligent electronics, trees and bushes that sway in the wind, as well as cats and other animals that should not be reported, are excluded by means of a software-based filter. Persons, on the other hand, are still recognised and detected accordingly. Due to the additional electronics and software control required, iHR sensors are considerably more expensive than conventional HF sensors.

Below are some examples of HF sensors including installation, technical design and detection range:

Sensors transmit and receive in the detection area
Module design with HF transmitter (bottom) and receiver (top)

ULTRASONIC MOTION SENSOR (UM)

The ultrasonic motion detector consists of an ultrasonic transmitter and a receiver and reacts to a change (target/actual value comparison) in the ultrasonic waves emitted by the detector and received as a reflection in the monitored area (so-called Doppler effect)

The area to be monitored has an oval shape. The ultrasonic waves are transmitted through the air. Therefore, ultrasonic motion detectors must not be installed behind curtains, above radiators, in the area of ventilation inlets or outlets, near strong sound sources or in the vicinity of loosely suspended objects (e.g. lamps).

Sensors transmit and receive in the detection area
Module structure with UM transmitter (left) and receiver (right)

Conclusion

  1. Always use HF sensors for indoor applications
  2. With IR sensors, there may be a delay in triggering due to the type of detection
  3. Always pay attention to the specified range and radiation angle of the sensor
  4. When using external detectors, always ensure that they are also suitable for the connected load (keyword R-L-C load)

Good luck with your next project.
Your Marc Dicker

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