Brooks Firetracker FT128 CIE - Smouldering Smoke Algorithm; Figure 35 Filtering Algorithm N-15 Graph

Technical / Programming Manual
FT128 Rev 2.2
103
An example showing the alarm algorithm "N-15" is shown in Figure 35, i.e. the step value
X = 5. The detector polling time t ≈ 2.56 sec.
Figure 35 Filtering Algorithm N-15 Graph
Explanations on Figure 35:
In this example, the week average sensor value is "10" (=1.0 %/m) at the "starting point",
i.e. due to contamination the pre-warning level has been adjusted to "32" (10+22) and the
fire alarm level to "40" (10+30). The sensor value is accordingly "10".
In this example, alarm algorithm "N-15" is selected, i.e. normal detection time 15 sec. and
normal sensitivity 3% (30). X = 5. The detector polling time t ≈ 2.56 sec. (In system FT128,
the detector polling time t ≈ 7 seconds and the step value "X" is according to Table 13 –
but the principle is the same.)
the sensor values and decision values at start are approx. equal ("10"). When smoke enters
the detector, the sensor values will increase and by the fourth polling be approx. "27". Since
27-10 > X=5, the decision value ("10") is increased by X=5 to "15". Next polling the sensor
value is approx. "45", i.e. the decision value ("15") is increased by X=5 to "20", and so on.
In this example the decision value never reach to the fire alarm level. When the sensor
value is reduced to approx. "25", the decision value is set to "30", because 35-25=10 >
X=5, i.e. the decision value ("35") is reduced by X=5 to "30", and so on.
These comments refer to the numbered points on the graph shown in Figure 35 above
1. The sensor value has here reached the pre-warning level but nothing will happen
since the decision value has not reached the pre-warning level.
2. The sensor value has here reached the fire alarm level but nothing will happen
since the decision value has not reached the fire alarm level.
3. The decision value has here reached the pre-warning level and pre-warning is
activated.
4. The decision value is here below the pre-warning level and the pre-warning is
automatically reset.
14.4.3 Smouldering Smoke Algorithm
The smoke from a smouldering fire causes the sensor value to rise very slowly but not
reach the fire alarm level. A smouldering fire can last for hours and sometimes days. To
be able to detect such a smouldering fire at an "early" stage, a smouldering smoke
algorithm is used.