7
MAN3038-2
DISCOVERY PRODUCT GUIDE
6
Optical/Heat Multisensor Detector
6.1
Operating Principles:
The Discovery Multisensor construction is similar to that of the
optical detector but uses a different lid and optical mouldings to
accommodate the thermistor (heat sensor). The sectional view (Fig
3) shows the arrangement of the optical chamber and the
thermistor.
The Discovery Optical/Heat multisensory detector contains an
optical smoke sensor and a thermistor temperature sensor whose
outputs are combined to give the final analogue value. The way in
which the signals from the two sensors are combined depends on
the response mode selected. The five modes provide response
behaviour which incorporates pure heat detection, pure smoke detection and a combination of both. The
multisensor is therefore useful over the widest range of applications.
The signals from the optical smoke sensing element and the temperature sensor are independent, and
represent the smoke level and the air temperature respectively in the vicinity of the detector. The detector’s
micro-controller processes the two signals according to the mode selected. When the detector is operating
as a multisensor (i.e. modes 1, 3 and 4) the temperature signal processing extracts only rate-of-rise
information for combination with the optical signal. In these modes the detector will not respond to a slow
temperature increase – even if the temperature reaches a high level. A large sudden change in temperature
can, however, cause an alarm without the presence of smoke, if sustained for 20 seconds.
Additional heat sensor information
Discovery optical/heat multisensor detectors manufactured from mid 2009 incorporate additional temperature
information that is intended for use in signal processing. Temperature data can be read separately by the
control panel (see Note 1) and used to validate an alarm signalled by the multisensor analogue value. An
example of this would be a high multisensor analogue value not accompanied by an increase in heat: this
would indicate that an agent other than smoke, e.g. steam, had caused the high analogue value.
The exact method of polling to make use of this feature is described in a Technical Sales document available
to panel partners. This feature offers protection from false alarms.
Figure 3 – Sectional View – Discovery Multisensor Detector
