VESDA VLC-400 Product Guide
VESDA by Xtralis
14
www.xtralis.com
Figure 2-6: Xtralis VSC Smoke Threshold Tab
2.5.7
Digital value reporting
The digital value used to indicate the obscuration level reported to the fire panel is dependent on the type of
detector set.
The calculation used is:
V = (T - F) * O/A + F
Where:
l
V = The analogue value limited to a maximum value of 127
l
F = The fault threshold (11 for optical and 23 for aspirating)
l
T = Apollo loop alarm threshold is 55
l
O = The current smoke obscuration reading
l
A = The alarm obscuration level (from the sensitivity mode data)
2.5.8
Delays
Smoke level that exceeds the current Alarm threshold is held off until the delay period has expired.
When the device goes into alarm the reported obscuration level will be 54 counts until the delay period for the
selected sensitivity mode has expired or until the obscuration level goes out of alarm (whichever comes first).
At this point the current obscuration level is then reported (refer to Figure 2-7).
Figure 2-7: Delay and Obscuration Level Reporting
Figure 2-7 shows the detector to holding the reported alarm level until the device has been polled and the alarm
reported to the panel. Additionally, an alarm level will be reported to the fire panel via three consecutive
addressed polls.
