Technical Documentation: Fire Detectors used in hazardous areas
P-DET/EX/RCE/PM5/GKa/110995 18 Autronica Fire and Security AS
2.3 BZ-32 functional description, drawing BZ-044C
This diagram shows, in detail, how the current flow in the hazardous area is
limited to an acceptable value. On page 12 you will find diagram and descrip-
tion of the barrier Z-667/Ex where the detector line (loop) is represented by a
resistor "R
S
".
The potential equalization terminal is, inside the barrier Z-667/Ex, shorted to
the system "earth".
Only one of the four possible branches is illustrated. The other branches, (1 to
3) would have been drawn in an equal manner. The following functional
description is referring to branch number one.
The current through the branch is fed from plus (1 + 2), through the emitter -
base resistor R
1
, through the barrier Z-667/Ex terminals 21 to 23, through the
detectors "D" (which are parallel connected in a numbers of 1 to 10), through
the barrier Z-667/Ex terminals 13 to 11, and from there to minus (3 - 4).
The emitter - base resistor R
1
is given a value to obtain a suitable voltage drop
so the transistor V1 does not conduct if none of the detectors is conducting.
The signal answer current, caused by any of the detectors, will increase the
voltage drop across R
1
, causing transistor V
1
to conduct, passing a much greater
current through resistor R
2
. This causes the greater part of the signal current to
pass through the transistor and it's collector resistor R
2
.
In this way the necessary signal current through any of the detectors is limited
to a value which is acceptable for consumption inside the hazardous area.
(Accepted by the zener barrier's internal resistance.
All (maximum 4) branches are functioning in the same way, and perform signal
on the same terminal bloc, X1.
Observe that each detector; D
1
, D
2
etc. to D
n
are individually addressed.
BZ-32
function
description
To Next Page
Loading...
