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 4.2.1.1 Considerations. Three major characteristics of infrared technology
should be kept in mind by the security system designer in selecting PIRs for
an application.
a) Infrared is emitted by objects because of their temperature.
PIR performance will be determined by the stability of the background and
the clothing of the intruder as well as his speed.
b) Infrared energy is transmitted without contact between the
emitting and receiving surfaces. Viewing of direct or reflected sunlight
should be avoided.
c) Infrared energy is invisible to the human eye. A PIR requires
line of sight. Care must be taken in positioning so that obstructions are
between receiving "fingers."
4.2.1.2
Planning Factors for Model Selection:
a)
Size and shape of each area to be protected.
b)
Number of areas to be covered and overlap requirements.
c)
Locations where it is not possible to locate a PIR.
d)
Optical and thermal environment
4.2.1.3 PIR Sensor Installation. Plan the installation so that expected
intruder motion is across the sensor's field of view. The optimum mounting
height is 6 to 9 feet, with primary point of aim about 18 inches above the
floor on the opposite wall. Where the expected intrusion motion is toward
the sensor, mount the sensor as high as practical such that it can be angled
downward. This will shorten the effective range but permit the intruder to
cross the sensor pattern.
4.2.1.4 PIR Sensor Location. PIR sensors respond to a change in infrared
energy resulting from a rapid change in temperature. A person entering a
detection area will cause an alarm signal. Sometimes a stationary object
which changes temperature rapidly, such as a light bulb which fails, can
cause an alarm. To avoid this, care must be taken in locating and aiming
the sensors.
4.2.1.5 PIR Sensor Positioning. The infrared energy to which the sensor
responds does not pass through glass or other building materials. However,
intense sunlight passing through glass and shining on the sensor may cause
an alarm. A metal wall or a window exposed to solar heat changes can cause
an alarm. The sensor should be positioned such that direct sunlight or
solar-heated walls are not in its field of view. Reflection from dark,
shiny surfaces should also be avoided. A PIR should be positioned to
prevent the
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