Xtralis VESDA VLC-505, Manual

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VESDA Pipe Network Design Guide VESDA by Xtralis
24 www.xtralis.com
4.10 Reference Sampling
Periodically, smoke and other pollutants from external sources may enter a protected zone temporarily raising
the smoke level. In this case the detector will detect the smoke and generate an alarm. Referencing is
employed to compensate for the periodic rise in smoke levels and to reduce nuisance alarms in high
sensitivity areas.
A separate VESDA detector is used to draw air from the external source and produce a reference reading of
the background level of smoke and pollutants. The reference reading is then subtracted from all VESDA
detectors monitoring the internal VESDA Addresses (also known as VESDA Zones). This allows the internal
VESDA detectors to determine if a rise in smoke levels is due to background pollution or a problem inside the
VESDA zone of protection. The ability to check the background level of smoke greatly reduces the chance of
detectors false alarming.
VESDA detectors in large installations typically operate at varying sensitivity levels. In such instances the
level of subtraction can be set differently for each detector.
Referencing is configured through Xtralis VSC, LCD Programmer or Xtralis VSM4 Software. Refer to the
respective manuals for details.
Legend
A Internal detectors D Reference area (Car park, Loading bay etc.)
B Reference detector E VESDAnet
C Reference sample pipe
Figure 4-26: Reference sampling