An Electronic sensor that senses infrared (IR) light emitted from objects such as IR Illuminators when found within a certain range is called a Passive Infrared Sensor or PIR sensor. PIR sensors are usually used in PIR based motion detectors in order to check the movement of an object.
Working of PIR Sensors
Every object that has a temperature above zero degrees emits energy in the form of radiations. This form of radiation is usually invisible to the human eye. It gets detected by devices that are specially designed to detect such kinds of radiations. The “P” in the PIR sensors stands for passive. This is because the sensor does not release any form of radiation or energy to detect objects. In fact, it detects the radiations emitted by the other object that may be within its field of view. Though these sensors do not have to emit any sort of energy, they are the most complicated sensors as compared to others like photocells. Let us go, through the basic of the actual working of a PIR sensor.
The Passive Infrared sensor has two main slots in it. Each of these slots is constructed in a way that they are more sensitive to IR lights. There is a lens attached in between. This lens helps in widening the area that is being detected. The two slots detect the slightest movement taking place within their reach. When the sensors are idle, i.e. there is no movement around the sensor, both the slots show the same amount of IR detected. When a warm body, such as a human or an animal comes closer to the sensor, one half of it is intercepted and this causes a positive differential change among the two slots. By the time the body moves out of the range, it causes a negative differential change.
PIR Sensors are useful in detecting minute changes in temperature as they can also detect radiations from Infrared Illuminators that are not visible to the human eye. It will prove to be helpful in detecting movements in areas where entry is restricted.