How Does an Infrared Alarm Sensor Work?
Infrared Defined Infrared radiation is a type of electromagnetic radiation similar to visible light but with a longer wavelength. Almost everything produces infrared light. The hotter something is, the more infrared it produces. Infrared is visible to some animals, but it can not be seen by humans without special equipment such as night vision goggles Infrared Detection Most infrared cells use a Cadmium Sulfide or CdS cell to detect infrared light. CdS cells are resistors–elements that resist the flow of electricity. CdS cells are special types of resistors called photoresistors. When they are exposed to light, their resistance goes down. The CdS cell in a motion detector is set up to only detect infrared light. The circuitry inside the motion detector monitors the cell’s resistance continuously and uses changes in the resistance to detect motion. Active Infrared In active infrared systems, an infrared laser shoots pulses of infrared light at the CdS cell, which is attached to a detec
