What are 'analogue' and 'digital' protocols?
The term 'analogue' is used to describe a signal which goes up
and down steplessly.
Signals that record phenomena such as the increase of smoke or
heat are necessarily analogue at source and this is why fire
detectors are described as analogue. For example, a heat detector
will record stepless increases in temperature from a typical
starting point of 20-21°C (comfortable room temperature) to an
alarm level of 55°C, however fast the increase.
Each point on the analogue signal indicates a particular value.
The problem with analogue signals, however, is that during
transmission, electrical corruption may affect the signal. A '2'
might then appear as a '3', for example.
The word 'digital' describes a signal that consists of a series
of '0s' and '1s' or 'offs' and 'ons' which go to make up a message
in binary arithmetic. The advantage of this system is that there is
a much lower risk of the signal being poorly transmitted and hence
giving wrong information.
Apollo fire detectors have always used a digital protocol which
has remained basically unchanged since its inception in 1986. It
has been extended-in two steps, once for XP95 and a second time for
Discovery - but never modified.
Most detector manufacturers have now adopted digital
A digital protocol is much less susceptible to corruption than
the analogue protocol and is to be preferred in a system which is
Apollo has a digital, open protocol.
For a fuller exploration of these issues, please download our
Protocols PIN sheet PDF.
Apollo's protocol is available to equipment manufacturers
subject to agreement by Apollo Fire Detectors. For details on
becoming an Apollo agreed protocol user, please contact our Technical Sales