Ampac Orbis, Product Manual, Page: 11 / 22

9
MAN1509-4
ORBIS AUSTRALIAN PRODUCT GUIDE
7 Where to use Heat Detectors
Heat detectors are used in applications where smoke detectors are unsuitable. Smoke detectors are
used wherever possible since smoke detection provides earlier warning of fire than heat detection.
There are, however, limits to the application of smoke detectors and these are described in the
section ‘Choosing a detector’.
Heat detectors should be used if there is a danger of nuisance alarms from smoke detectors.
The Orbis range incorporates four heat detector classes to suit a wide variety of operating conditions
in which smoke detectors are unsuitable.
All heat detectors in the Orbis range are tested as static or rate-of-rise detectors and are classified
as such.
7.1 Orbis heat detector
The Orbis range incorporates four heat detector classes to suit a wide variety of operating conditions
in which smoke detectors are unsuitable.
7.2 Choosing the correct class of heat detector
Heat detectors have a wide range of response characteristics and the choice of the right type for a
particular application may not always seem straightforward. It is helpful to understand the way that
heat detectors are classified as explained earlier and to memorise a simple rule: - use the most
sensitive heat detector available consistent with avoiding false alarms.
In the case of heat detectors it may be necessary to take an heuristic approach, ie, trial and error,
until the best solution for a particular site has been found. The flowchart above will assist in choosing
the right class of heat detector.
Old Terminology Dot Colors New Terminology Temperature Range
A White BR (Rate of Rise) 55 - 88
˚C ( “R” Rate of rise)
B Blue A2S (Static) 55 -
88˚C (“S” Static)
C Green CR (Rate of Rise) 88 -
132˚C ( “R” Rate of rise)
D Red CS (Static) 88 -
132˚C ( “S” Static )
7.3 How do orbis heat detectors work?
Orbis heat detectors have an open web casing that allows air to flow freely across a thermistor which
measures the air temperature every 2 seconds. A microprocessor stores the temperatures and
compares them with pre-set values to determine whether a fixed upper limit, the alarm level, has
been reached.
In the case of rate-of-rise detectors the microprocessor uses algorithms to determine how fast the
temperature is increasing.
Static heat detectors respond only when a fixed temperature has been reached. Rate-of-rise
detectors also have a fixed upper limit but they also measure the rate of increase in temperature. A
fire might thus be detected at an earlier stage than with a static detector so that a rate-of-rise
detector is to be preferred to a static heat detector unless sharp increases of heat are part of the
normal environment in the area protected by the heat detector.
7.4 Environmental performance
The environmental performance is similar to that of the Orbis optical smoke detector but it should be
noted that heat detectors are designed to work at particular ambient temperatures (see Figure 3).