Considerations; Avoid Removing Iop A; Iop A Preference; Replacing The Fta Switching Module - Honeywell HPM Service

4 Fault Isolation
4.6 Redundant Analog Output IOP Failure Diagnosis
Analog Output IOPs, but it should improve your approach to locating, isolating, and correcting a
problem.

Considerations

A knowledge of the information provided by the Universal Station displays, detailed in the "UCN Status
Displays" section and discussions in early subsections of the "Fault Isolation" section is needed to
understand a systematic troubleshooting procedure. Consider the following information and suggestions.

Avoid removing IOP A

If at all possible, do not remove IOP A. The IOP A is the IOP connected by cable to the FTA Cable A
connector, J1, on the Analog Output FTA.

IOP A preference

Redundancy for the Analog Output IOPs is biased toward IOP A. A hardware bias exists because IOP B
(the physical secondary) is connected to the Analog Output FTA through a switching module on the
FTA, while IOP A (the physical primary) is connected directly to the FTA circuitry that interfaces the
FTA's field wiring outputs.

Replacing the FTA switching module

The switching module can be replaced without disturbing the FTA's outputs when IOP A is the primary
IOP because IOP A has a direct connection to the field wiring terminals, independent of the switching
module's presence.

Switch to IOP A when a Soft failure occurs

If the IOP pair has a Soft failure because of a redundancy hardware problem, and IOP B is the primary
IOP BSF/SF** on the HPM Status display] and still in synch, it is important to switch to IOP A before
proceeding. Once IOP A becomes the primary IOP, replacement of IOP B, or the switching module on
the FTA, can occur without the loss of outputs to the field.
** The "XX/YY" represents the status shown on the HPM Status display. The correct interpretation

is that "XX" is IOP A, and "YY" is IOP B. The backup IOP is identified by either "BKP" or "BSF."

Consider use of an AO Standby Manual device

If the user is conservative, you can always connect an Analog Output Standby Manual device to the FTA
and then replace either the Analog Output IOP or the switching module on the FTA. However, you must
realize that with the Analog Standby Manual device in place, all control points using these outputs will
go into initialization.
352 HPM High-Performance Process Manager Service
Honeywell
R688
December 2020