Infrared Sensor Buying Advice
Infrared motion sensors can be an important component in home security. We now all knew that the body of the any human being or the animal could emit the infrared rays. Infrared radiation exists in the electromagnetic spectrum at a wavelength that is longer than visible light. It can not be seen but it can be detected. Objects that generate heat also generate infrared radiation and those objects include animals and the human body whose radiation is strongest at a wavelength of 9.4um.
Infrared in this range will not pass through many types of material that pass visible light such as ordinary window glass and plastic. However it will pass through, with some attenuation, material that is opaque to visible light such as germanium and silicon. An unprocessed silicon wafer makes a good IR window in a weatherproof enclosure for outdoor use. It also provides additional filtering for light in the visible range.
It is important to survey your home and determine where you intend to put an infrared sensor. You can choose areas where an intruder is likely to go. Common locations are in a hallway or stairway. Please remember that a passive infrared motion sensor detects heat. Eliminate spots where you must aim at heat vents, radiators, open windows where sunlight shines through, or windows where car headlights often shine through at night. It is suggestible that buyers select either a hard-wired or wireless motion sensor,
which will depend on whether you have a hard-wired or wireless security system. If you have a hard-wired system, you need to drill holes in walls and route wires in and out of walls to the control panel. There will be a power source for a wireless motion sensor. Some infrared and dual technology motion sensors, however, come with a lithium battery that supplies power.
When using a passive infrared sensor and if you have to aim it where a heat source is located; you can mask the sensor so that it doesn't "see" that heat source. An infrared sensor includes a concave mirror that looks like a fly's eye - a lot of notches on it. Each notch is pointed toward a different direction, and each notch watches a particular area of the room. If a heat source is within sight of the sensor, you need to determine which notch is watching that area and mask it with electrical tape
so that the sensor will no longer see the heat source.
The pyroelectric sensor is made of a crystalline material that generates a surface electric charge when exposed to heat in the form of infrared radiation. When the amount of radiation striking the crystal changes, the amount of charge also changes and can then be measured with a sensitive FET device built into the sensor. The sensor elements are sensitive to radiation over a wide range so a filter window is added to the package to limit incoming radiation to the appropriate range which is most sensitive to
human body radiation.
Typically, the FET source terminal pin 2 connects through a pull down resistor of about 100 K to ground and feeds into a two stage amplifier having signal conditioning circuits. The amplifier is typically bandwidth limited to below 10Hz to reject high frequency noise and is followed by a window comparator that responds to both the positive and negative transitions of the sensor output signal. A well filtered power source of from 3 to 15 volts should be connected to the FET drain terminal pin 1.
Buying Tips:
Infrared motion sensors are important to every home when thinking about home security. When buying infrared sensor, pay special attention to the lens used for you selection cause it affects the response speed of your sensor. Also, backup battery is crucial as you don't want your infrared motion sensor to cease functioning if there is a blackout.
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