4.10 Hpm Alternate Private Path; Overview - Honeywell HPM Service

4.10 HPM Alternate Private Path

Overview

This maintenance procedure allows the redundant operation of the HPM to be restored after the failure of
certain Private Path interface components in a primary HPM Comm/Control card.
Background
HPM Private Path failures can occur where the secondary HPMM fails, but the primary HPMM has the
failed hardware. The failure itself does not interrupt control, but redundant HPMM operation cannot be
restored until the primary HPMM is repaired, requiring control to be shut down.
When the Private Path fails and the software cannot determine which HPMM controller contains the
defective hardware, the software will fail the secondary HPMM controller. This assumption minimizes
the probability that control will be lost. If the software were to fail over, there would be no way to fail
back should the secondary HPMM be unable to assume control.
If the defective hardware is in the primary HPMM, the standard Private Path cannot be used to restore
redundant HPMM operation unless control is shut down and the primary HPMM controller is replaced.
The HPM has an Alternate Private Path. The Alternate Private Path contains an independent set of
interface drivers and receivers that can be used to restore redundant HPMM operation should the
standard Private Path drivers or receivers fail. The Alternate Private Path is intended for temporary use
only. It is not mechanically robust enough for continuous use.
When to use the procedure
This procedure should be used only when the all of the following conditions are true.

A failure has been reported for the secondary HPM Comm/Control card of a redundant HPMM pair
with the failure code indicating a Private Path failure.

After replacing the secondary HPM Comm/Control card and the backpanel redundancy cable, the
secondary HPMM loads without error but will not synchronize with the primary HPMM.

The Primary HPMM is still controlling the process.
When these conditions exist, it is reasonable to assume that the secondary HPMM is functional and that
the primary HPM Comm/Control card's Private Path interface circuits have been damaged.
R688
December 2020
HPM High-Performance Process Manager Service
Honeywell
4 Fault Isolation
4.10 HPM Alternate Private Path
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