Brooks Firetracker FT128 CIE - Filtering Algorithm; Table 13 Smoke Detector Alarm Algorithm

Technical / Programming Manual
FT128 Rev 2.2
102
 Normal (15 sec.) or slow (35 sec.) detection time (alarm delay)
Normal sensitivity. (Default) Fire alarm offset is 3.0 % smoke obscuration per meter.
High sensitivity. Fire alarm offset is 2.4 % smoke obscuration per meter, i.e. less than for
normal sensitivity. Can be used when an "early" fire alarm is required.
Low sensitivity. Fire alarm offset is 3.6 % smoke obscuration per meter, i.e. more than
for normal sensitivity. Can be used to reduce nuisance alarms.
Normal detection time (15 sec.) (Default) There will always be min. 15 seconds alarm
delay
112
. This is a "normal filter" to reduce nuisance alarms.
Slow detection time (35 sec.). There will always be min. 35 seconds alarm delay
112
. This
is an "extra filter" to reduce nuisance alarms but might not fulfil the AS7240.7 requirements.
Each analogue smoke detector can have two alarm algorithms programmed via EBLWin.
One Regular alarm algorithm that is normally used (N-15 is default) and one Alternative
alarm algorithm that is turned on/off via a time channel (internal or external) e.g.
normal sensitivity can be used during night-time and low sensitivity during daytime i.e. the
alternative alarm algorithm is used to reduce nuisance alarms during working hours.
The alarm algorithm in use can be read in menu H4/U3.
14.4.2 Filtering Algorithm
In order to secure a fast detection of real fire alarms and to reduce nuisance (false) alarms
to a minimum, a filtering algorithm is used.
The filtering algorithm uses the sensor value to calculate a decision value depending on
which alarm algorithm that is used.
The decision value starts at zero. Each time a new sensor value is picked up (sampled)
from an analogue smoke detector 430x/440x, this new sensor value is compared with the
actual decision value, which will be adjusted if required, see below.
If the difference, between the new sensor value and the actual decision value is < "X", the
decision value is set equal to the new sensor value.
If the difference is > "X", the decision value is increased or reduced by "X".
"X" = The Step Value, It is different depending on the sensitivity and detection time, i.e. it
is dependent on the selected alarm algorithm, see Table 13 below.
The decision value will consequently not be increased / decreased with a value exceeding
the "X" value even if a sensor value is much higher / lower, see Figure 35.
There are six alarm algorithms. The default is alarm algorithm N-15, i.e. normal detection
time (15 sec.) and normal sensitivity (3%). "X" is the step value.
Note: The L-15, H-35, N-35 and L-35 algorithms may not comply with AS7240.7
requirements.
Table 13 Smoke detector alarm algorithm
Analogue detector
Normal detection time (15sec.)
Slow detection time (35sec.)
H-15
2.4%
High
sensitivity
N-15
3.0%
Normal
sensitivity
L-15
3.6
Low
sensitivity
H-35
2.4%
High
sensitivity
N-35
3%
Normal
sensitivity
L-35
3.6%
Low
sensitivity
4300
113
/ 4301
114
4400 / 4401
X=8
X=10
X=12
X=4
X=5
X=6
112
After the fire alarm level is reached / passed, it will take min. 15 alt. 35 seconds until fire alarm will be activated in the CIE
113
4300 is replaced by 4400.
114
4301 is replaced by 4401.