Occupancy sensors are known by different names such as motion sensors or switches, movement detectors or even automatic light switches and presence detectors. There are 5 main different kinds of Occupancy sensors available in the market today based on the technology used to detect occupancy.

  1. PIR based sensors
  2. Ultrasonic based sensors
  3. Microwave based sensors
  4. CW Radar based sensors
  5. Thermal Imaging based image processing sensors

All the above mentioned technology sensors except for the thermal image processing sensor  use the primary factor of motion or movement of an object as the key determinant to flag for occupancy. The application of these sensors has been mostly in the field of security, residential and industrial automation and electrical energy conservation.


PIR sensors:

The most widely used sensors in the market in terms of utility, energy savings and cost savings are PIR(Passive Infrared) based sensors. These sensors detect human or automobile motion or movement and switches ON any electrical/electronic device to which it is connected to. The key component of the sensor module is the pyro-electric element. There usually is a minimum of 2 elements which enable noise cancellation and enhanced detection.

Passive infrared sensors as the name suggests detect changes in IR(infrared radiation) that is triggered by any hot moving body such as human or any other warm blooded animal movement, automobile movement or even a warm breeze. All this motion represents a time varying IR shift which triggers small signal fluctuations in the pyroelectric element. These small signal fluctuations are amplified and signal conditioned in the signal conditioning circuit.

One important aspect of PIR sensors is that the front end sensor is a passive energy component which implies that it does not actively emit energy in order to detect motion. Hence, during prolonged idle operations when there is little or no movement that is to be detected, these sensors are more energy efficient. Further, this feature attains higher prominence when these sensors are being used for electrical energy conservation through applications such as automated light switches since the self energy consumption of PIR control switches is minimal.  


Ultrasonic sensors:

These sensors fall into the category of active sensors because the front end sensor actively emits sound waves at ultrasonic frequencies which in turn require a continuous supply of energy for the sensor.

Ultrasonic sensors unlike PIR sensors have a continuous detection field which is un-segmented thus eliminating the prospect of dead zones where small movement detection becomes impossible.

However, the major drawback of these sensors is false activation or nuisance triggering since the ultrasound detection range can leak into adjacent spaces where motion detection is undesirable. Further, any movement of inert specimens such as temperature stabilized or random airflow can trigger these sensors. When used for electrical energy conservation purposes such as in automated light controls, it partially loses its purpose since the self energy consumption is much higher when compared to PIR sensors.


Microwave sensors and CW(Continuous Wave) Radar based sensors:

Microwave sensors and CW Radar sensors are quite similar to ultrasonic sensors since these sensors also belong to the category of active sensors and also have transceiver elements which can both emit and detect microwave and CW radio signals. The major difference between a microwave/CW radar sensor and an ultrasonic sensor is that microwave and CW radar sensors emit electromagnetic waves unlike high frequency sound waves emitted by an ultrasonic sensor. These sensors are usually more cost and energy expensive than ultrasonic sensors. In terms of relative merits and de-merits they are on par with ultrasonic sensors.


Image processing sensors:

Sensors based on image processing are used in occupancy sensing applications where the area to be sensed is highly segmented. The best example for a segmented sensing of occupancy would be the aisles of a supermarket store. Each aisle can be monitored using individual or a wide angle camera. The video feed can be image processed in a control and processing unit to detect human occupancy which in turn can control light fixtures or other smart product address systems to customers in different aisles. The main shortcoming of this type of a sensor unit is its very high initial setup cost.   

Thus, by comparing the overall cost-performance benefits of the different types of sensors available, we can see that the most versatile type of sensor is the PIR based sensor simply because of its cost effectiveness and easy adaptability for various applications. The SIRIUS brand PIR based occupancy sensors and motion sensor switches are renowned the world over for its quality and reliability.

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