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PIR Motion Sensor
The
P
assive
I
nfra
R
ed (PIR) sensor will, under typical conditions,
detect a human being moving around within approximately thirty
feet (about 10m) from the sensor. This is an average value, as the
actual detection range is between 16ft/5m and 50ft/15m.
As the performance of the sensor is determined primarily by
environmental conditions, no guarantees can be offered regarding
the detection range. However, the range is typically sufficient for
the majority of interior spaces (excluding the obviously absurd,
such as basketball courts or aircraft hangars). Some garages may
be large enough that one sensor cannot cover the whole area –
we suggest testing this in the actual environment if there’s any
doubt.
The sensor has a 110º field of view horizontally, and a slightly
narrower view vertically. This means that most of what you could
see if you closed one eye and put your head where you’d mount
the sensor is pretty close to the area the sensor will cover. The
main blind spots, of course, are above, below or behind the sensor
itself.
Typically, the ideal placement in an environment is in the upper
corner of a room, facing slightly towards the ground (perhaps 20-
25º, depending on the height of the sensor). Try to cover typical
paths through the room, focussing particularly on likely entry and
exit paths. If the room has several entry points, try to cover as
many of these as practicable.
A visible PIR sensor can be a great deterrent to intruders – but
on the other hand, skilled intruders can avoid obviously placed
sensors. Try to mix it up a bit.
How it works:
The PIR sensor is a
passive
infrared motion sensor, meaning it detects infrared
radiation rather than projecting it (unlike a security camera with infrared night
vision, which is
active
infrared). All objects emit this “black-body” radiation (we
commonly call it “heat”) and the infrared sensor looks for any of this radiation
which moves.
The passive sensor is not infallible – in particular, it cannot detect objects/people
which are the same temperature as their background. So a human being moving
about on an extremely hot day might go unnoticed. Also, a security camera with
active infrared night vision in the same vicinity as the infrared sensor may give false
alarms (particularly if it is a moving PTZ system).
The PIR Sensor
A PIR Sensor
