advertisement
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.
MAN3038-2
Figure 3 – Sectional View – Discovery Multisensor Detector
7
DISCOVERY PRODUCT GUIDE
Mode
Smoke
Sensitivity
(grey smoke)
%/m dB/m
Temperature
Sensitivity
Response
Type
Minimum
Time to Alarm
(seconds)
1
2
3
4
1.1 0.05
2.1 0.09
2.8 0.12
4.2 0.19
>15°C
Increase
Not set to heat response
>21°C
Increase
>15°C
Increase
Multisensor
Optical
Multisensor
Multisensor
5
No response to smoke
Refer Mode 5 below
Heat A1R
Table 2 – Multisensor Detector Operating Modes
Characteristics of the response modes
The processing algorithms in modes 1 to 4 incorporate drift compensation.
The characteristics of the five response modes are summarised below.
20
30
20
20
15
Mode 1 has very high smoke sensitivity combined with high heat sensitivity. This gives a high overall sensitivity to both smouldering and flaming fires.
Mode 2 has a smoke sensitivity similar to that of a normal optical smoke detector. This mode is therefore equivalent to a standard optical detector. It is suitable for applications in which wide temperature changes occur under normal conditions.
Mode 3 has moderate smoke sensitivity combined with a moderate sensitivity to heat. This combination is considered the optimum for most general applications since it offers good response to both smouldering and flaming fires.
Mode 4 has lower than normal smoke sensitivity combined with high heat sensitivity. This makes it suitable for applications in which a certain amount of fumes or smoke is considered normal.
Mode 5 has no smoke sensitivity at all, but gives a pure heat detector response meeting the response time requirements for a Class A1R detector in the European standard EN54–5:2000. In this mode the detector will respond to slowly changing temperatures and has a “fixed temperature” alarm threshold at 58°C. The analogue value in this mode will give the approximate air temperature over the range 15°C to 55°C.
In mode 5, the smoke sensor is still active though it does not contribute to the analogue signal. As a consequence, if the detector is used in a dirty or smoky environment the optical sensor drift flag may be activated in the heat-only mode.
Notes
•
This applies only to panels which have been programmed to read the additional information.
•
In situ testing of the Multisensor detector should be carried out as for smoke detectors in response mode 2 and for heat detectors in response mode 5. Both optical and heat sensors must be tested in modes 1,3 and 4.
•
If the Multisensor is to be used in mode 5, heat detector spacing/coverage should be applied.
6.2 Product Codes
Product Description EN54-5 & 7 (CEA4021) AS7240-15
Discovery Multisensor Detector 58000-700AMP 4106-2008
AS1603-1 & 2
201-0094
(58000-730)
8
MAN3038-2
advertisement