Technical / Programming Manual
FT128 Rev 2.2
92
11 Short Circuit Isolators
4313 Analogue base with isolator has built-in short circuit isolator that requires a separate
COM loop address and a Sequence Number, 00-63.
The units 4433, 4439 and 4477 have built-in isolator that do not require any separate COM
loop address, only a Sequence Number, 00-63. As an option, these units can be used
without the isolator in function. If so, they have to be programmed in EBLWin as if they
were 3333, 3339 and 3377 units and via the address setting tool 4313/4413 set to 2330
mode instead of NORMAL mode.
An open circuit (break) or short circuit on the COM loop has to generate a fault in the control
unit within 60-100 seconds.
If one or more Short Circuit Isolators are used
, the loop will be divided into "segments"
(i.e. the part between two Short Circuit Isolators or between the control unit and one Short
Circuit Isolator). Only the affected segment will be isolated, which will minimise the number
of units disabled by a short circuit.
The fault messages will also show between which isolators the short circuit is situated.
Figure 31 Short Circuit Isolators example in FT128
The first isolator (ISO) in the A-direction must have the sequence no. 0 (ISO no. 0), the
next sequence is no. 1 (ISO no. 1) and so on. The sequence no. is programmed via
EBLWin.
If no Short Circuit Isolators are used, the whole COM loop will be disabled in case of short
circuit on the loop.
As from version 2.1.x, the communication (and power supply) direction will alternate every
22 seconds.
COM loop end-point voltage
<12 VDC or COM loop short circuit or COM loop
break(s):
This will start a "cycle" as follows.
The whole loop will be disabled, i.e. no voltage on the loop which means that all
isolator relays will be powered down (= all isolators disabled), i.e. there will be a
“break” on the L (SA) wire in each isolator.
A control unit algorithm will now try to re-enable the first isolator in the A-direction
(ISO no. 0 / sequence no. 0). If this is possible, the next isolator in the A-direction
At least one short circuit isolator must be install every 40 alarm points as required by AS1670.1.
When communicating in the A-direction.
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