PASSIVE INFRARED DETECTOR
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-045 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 number 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.
Interface Module PIR-IF485A and Installation Software
The Installation Software is very useful for alignment and signal check during setting up and routine maintenance. It will
indicate the amplitudes generated by wanted as well as unwanted targets and help setting the gain control correctly during
walk tests and also show the magnitude of disturbance signals. The installation software is to be installed on a PC; an
interface module is required to convert RS 232 to RS 485. The information for installation and signal monitoring is displayed
on the screen of the PC. Refer to annex 3 for more details.
If more than one detector is connected to the same RS 485 communication bus, each detector needs to have a different
identification number. The interface module PIR-IF485A is available as an
accessory and is pre-configured and equipped with
the necessary connectors to be operated with any
detector of the IR 450 Series without the need for
external power supply or other connections.
The input cable is 4.0 m long and is terminated with a
connector fitting into the test socket on the connector
board of the detector.
The connection to the PC’s COM port is with a
standard 3.0 m cable (supplied with the PIR-IF485A).
Total weight of the PIR-IF485A with cables is app.
400g.
