Automatic Door Sensor Technologies

Most sensors for the automatic door market are not created and used equally. In fact, when it comes to safety and energy savings, sensors has one of the most contributions because it signals to the door when to open and close. In this article, you will explore the major type of technology of automatic doors sensors in the market today.


1. Microwave Sensors

Microwave automatic door sensors function by utilizing the principle of Doppler effect to detect motion. The sensor emits electromagnetic waves which are microwaves at a certain frequency continuously in a defined zone or area. These microwaves are reflected back to the sensor upon hitting the objects, floors or walls.

Stationary objects: The microwaves will be reflected back with the same frequency as the emitted microwave. When the sensor does not have any difference in frequency, no detection will occur.

Moving objects: Once there is a moving object or person in the zone, then the microwaves is “interrupted” by the moving object causing its frequency to change.  The microwave come back to the sensor with a different frequency and this results in a detection.

Since microwave sensors can detect the changes in frequency, this technology is best used for detecting motion. Furthermore, this technology can differentiate between an approaching movement and a departing movement. The sensor will only trigger the door to open during an approaching movement, which helps in keeping door closed most of the time and generate energy savings.

However, one of the downsides of microwave sensors, is that it cannot detect stationary objects or people, which would need microwave sensors to be combined with the next technology below.


2. Active Infrared Sensors
2.1 Safety Beams / Photocell

Safety beams are usually installed on the doors frames of the door opening, preventing the door from closing prematurely if there is a person or object near it. The transmitter and receiver are installed opposite each other, forming an “invisible line”. If there is no obstruction and the line is continuous, then the door can close. However, when a person or objects cut or interrupts this “invisible line” between the transmitter and receiver, the door is prevented from closing.

2.2 Active Infrared Sensors

An active infrared automatic door sensor is, by definition, a sensor that emits infrared light in a well-defined area and analyzes the reflections that come back. To put it simply, this sensor functions by taking a snapshot of the defined area. The sensor registers this and use this as a reference. If there is an object, person or movement in the defined area, then the snapshot of the defined area now changes, then the sensor will provide an activation signal.


Since infrared sensors can detect stationary and moving objects, they are used as a presence detection in most automatic sliding doors. Furthermore, this can be combined with microwave in one combination sensor (motion and presence) for a great aesthetic look and complete functionality.


3. Passive Infrared

Passive infrared automatic door sensors work on the basis of ambient temperature. The infrared sensor registers a thermal image of the defined zone. The sensor reacts if any object of person radiate a particular temperature in the defined zone.  To be more specific, in order for the sensor to be activated, (1) there must be a temperature difference of +/- 1 °C between the object to be detected and the background. (2) The object to be detected must move at a rate of at least 4 inches per second.

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