World Patents Pending ©AirSense Technology Ltd. 1999
ISSUE 2.4
Page 32
T E C H N I C A L
.
M A N U A L
of the rooms as a result of a change in conditions in another room. Such causes are very
difficult to trace. The only solution in this instance is to have individual referencing in
each room and the ability to turn it off when it is not required. With individual
referencing a reference detector will be sited at the inlet to a room and will reference a
detector at the outlet. Problems can still occur due to the change of flow rates, but the
requirements for a particular room can be analysed and errors can be identified as
originating from a given room.
Because of the difficulties associated with complex systems, the Stratos detector does
not cater for transport delays or rooms with a very long time constant. The general
advice to system designers is to keep a reference system as simple as possible because
of the inherent pitfalls.
Stratos does contain a function to program in the filling time constant which is
separately programmable for each detector in a system. The variations of smoke density
and signals associated with this are shown in Fig. 6. The intent is to modify the reference
signal such that:-
[modified sig. representing]
[signal representing]
[signal representing]
[pollution entering the area] - [pollution leaving the area] = [pollution added from]
[within the area.]
There are two variables which can be programmed into the Stratos which modify the
reference signal to suit it to the situation of the detector. The first is the filling time
constant and the second is the attenuation. The effect of these on the reference signal
is illustrated in the curve “
MODIFIED
REFERENCE
SIGNAL
” in Fig. 6. The filling time constant
entry is labelled as “Reference back off time delay (mins)” in function 8. This should be
set to be equal to the filling time constant and has a maximum value of 99. It will modify
the reference signal for the one detector concerned by providing an inverse exponential
rise and fall to the reference signal. The second programmable variable is “Reference
level” at function 7. This should be set to be equal to (1 - E) where E is the efficiency
of a relevant filter as defined above. It is the factor “K” shown in the curve “
MODIFIED
REFERENCE
SIGNAL
” in Fig. 6. The purpose of these two programmable variables is to match
the effect of external reference to the response to external pollution of the detector at
the outlet. Perfect matching will only be achieved if there is very good mixing in the
Stratos detector
referencing
