PIR-018
PASSIVE INFRARED DETECTOR
2824-00005 Page 5 of 10
Alarm Time
Alarm time and count per event is determined by the duration of the detected event and depends on the shape and amplitude
of the alarm signal. Individual alarm pulses have a minimum time of app. 2.0 s.
Internal Temperature Compensation
The PIR-018 is detecting radiation differences of a target against its background. In the course of the day and year the
contrast of a person will vary considerably and affect the signal strength. To compensate for this contrast variation, the PIR-
018 has internal temperature compensation with maximum sensitivity at app. 30°C (where the contrast of a human target is
weakest) and gradual reduction at higher and lower temperatures.
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When installing a unit the internal temperature may take up to 30 minutes or more to stabilise to the actual external
temperature. Sufficient time should be given to the PIR-018 to reach the correct internal temperature and sensitivity
before performing walk tests.
During the initial period of operation it is strongly recommended that walk tests are repeated and signals monitored under
various weather conditions such as high and low temperatures, wind fog, snow, rain etc. to obtain comparative data and
information on the effects of environmental conditions on detection and nuisance alarm probabilities for this particular site.
Fine-tuning of the detector based on this data by changing the sensitivity settings may optimise the performance.
External Sensitivity Adjustment via RS 485 Data Bus
If the
DIP - Switches 1 and 2
are both set to
„on“
, the detection performance can be adjusted via the RS 485 two way
communication port. Overall sensitivity of the PIR-018 can be set to any value between 20 and 140 %.
The external sensitivity adjustment may also be used if overall sensitivity has to be
changed at certain periods of the day or year depending on the prevailing thermal
contrasts. Field tests in the actual environment will determine the optimum settings. For
further details refer to annex 3.
Signal Processing
The background noise is sampled at a rate of app. 400 per second and averaged over a large num ber of cycles giving a
noise dependent value for the alarm threshold and to start the signal shape analysis whenever a certain amplitude value is
exceeded.
If the threshold has temporarily been increased by high background noise or repeated movements in the field of view, the
exponential decay of the threshold level to its original value will take app. 1 … 2 minutes from the end of the event.
Once the first threshold level value has been exceeded, the microprocessor starts its signal shape analysis routine where a
number of interdependent parameters including peak amplitude, rate of rise, time windows and overall shape are calculated
and analysed.
If the rate of rise of the signal is too high, as may happen as a result of RF interference, lightning, shock waves or birds flying
across the field of view close to the unit, a possible alarm will be rejected. This means also that a very fast movement directly
in front of the detector may not lead to an alarm even though the amplitude would be large enough.
Only if a signal meets all the predetermined criteria an alarm will be generated.
