IRACS and Infra Red
IRACS uses a modulated infra-red light beam to link transmitters to the nearby Receiver.Infra red light is invisible to humans, being of longer wavelength than we can discern. Not only the special LEDs (Light Emitting Diodes), but also any hot or glowing object will also radiate Infra Red energy.
Fortunately for us, it is possible to modulate the signal from the Transmitters so that it is not a continuous beam, but is 'chopped up' in a predetermined way.
The IRACS Receiver has one or more infra-red sensitive photodiodes built into it. These convert the infra red energy that they receive back into electrical signals, some part of which might have come from an IRACS Transmitter. By picking out the characteristic part of the signal and analysing it digitally, the Receiver can determine whether the signal is of the correct form to be an IRACS signal.
It is possible that other variations in the level of infra red seen by the Receiver can appear to be genuine IRACS signals, so several levels of checking are applied in order to weed out the often weak genuine signals from the background level. The success of this depends on the Receiver having enough genuine signal to work with compared with the level of unwanted signals - if the unwanted signals are too large, the Receiver cannot reliably re-form the Transmitted data. This causes range to be reduced, since the closer the Transmitter is to the Receiver, the stronger will be the received signal.
When the Receiver has built a valid set of information from the signals it has received, it passes this data set on to the IRACS Controller Console. Here, a further set of validity checks is performed before the data are verified against the table of Allowed or Blocked Transmitters. Only fully validated signals that have been Allowed to operate the Lift are accepted.