19
MAN3038-2
DISCOVERY PRODUCT GUIDE
10
Heat Detector
10.1 Operating Principles:
Discovery heat detectors have a common profile with ionisation and
optical smoke detectors but have a low air flow resistance case
made of self extinguishing white polycarbonate.
The Discovery Heat Detector uses a single thermistor to sense the
air temperature at the detector position. The thermistor is connected
in a resistor network, which produces a voltage output dependent on
temperature. The design of the resistor network, together with the
processing algorithm in the microcontroller, gives an approximately
linear characteristic from 10°C to 80°C. The linear signal is further
processed, depending on the response mode selected, and
converted to an analogue output.
For the European standard version of the detector, the five modes correspond to five “classes” as defined in
EN54–5:2001. The classes in this standard correspond with different response behaviour, each of which is
designed to be suitable for a range of application temperatures. All modes incorporate “fixed temperature”
response, which is defined in the standard by the “static response temperature”. The application
temperatures and static response temperatures for all response modes are given in Table 6.
In addition to the basic classification, a detector may be given an “R” or “S” suffix. The “R” suffix indicates
that the detector has been shown to have a rate-of- rise characteristic. Such a detector will still give a rapid
response even when starting from an ambient temperature well below its typical application temperature.
This type of detector is therefore suitable for areas such as unheated warehouses in which the ambient
temperature may be very low for long periods.
The “S” suffix on the other hand indicates that the detector will not respond below its minimum static
response temperature even when exposed to high rates of rise of air temperature. This type is therefore
suitable for areas such as kitchens and boiler rooms where large, rapid temperature changes are considered
normal.
Figure 5 – Sectional View – Discovery Heat Detector
