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 transmission protocols.

A digital protocol is much less susceptible to corruption than the analogue protocol and is to be preferred in a system which is life-critical.

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 Department.