2023-03
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H-System – Isolated Barriers and Termination Boards
Operation
5.2 Fault Output
Several H-System isolators monitor the field cables for lead breakages and short circuits
so that faults in the plant can be detected immediately. Line faults are prevented from being
interpreted as signals.
Depending on the configuration of the devices, these faults are transmitted to the outputs
at the control side and in separate fault indication outputs as additional information.
Fault Indication Output
Line and device faults are transmitted if the device has a fault indication output (FAULT).
The fault indication output is active in a normal state and inactive in a fault state (closed-circuit
principle). It is impossible to reverse the detection direction of the fault indication output.
Figure 5.1
Line Fault Transparency (LFT)
Line fault transparency makes electrical conditions on the field side visible on the control side
of the isolator. This enables line faults between the isolator and the field device to be detected
and transmitted to the control system via the signal line.
Figure 5.2 Example of line fault transparency with digital input
Fault Signal on Termination Board
The majority of the termination boards have an internal fault signal.
Information about a missing supply voltage of the termination board is available for the system
as a volt-free contact.
Wiring errors from field side will be reported via the same relay contact, if this function
supported by the isolators and the termination board.
1b
SL2
5a
5b
SL1
8a
7a
24 V DC
FAULT
1a, 1b
2a, 2b
6b
FAULT
SL2
5a
5b
SL1
8a
7a
Danger!
Explosion hazard from changing the fuse
The changing of the fuse under voltage can cause sparks. This can ignite the surrounding
potentially explosive atmosphere.
De-energize the device before changing the fuse.
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