Answer / carl_ellis

The situation is not unique to Allen Bradley; many
controller brands have I/O modules that can be replaced
without powering down the controller which might require
stopping the process.

The marketing term is the acronymn RIUP, Removal and
Insertion Under Power

The guys in the shop call it, "hot swap", hot meaning "while
powered", swap meaning to change out.

RIUP (Removal and Insertion Under) means that while the rack
is powered, any of the I/O Modules can be removed or inserted:
• With no physical damage to the module, to the rack, or to
other modules in the rack
• Without disturbing the functions of other I/O modules in
the rack or in the system.

It does not mean that the process will not be disturbed.

If an I/O card needs to be changed out under power, it means
that something is wrong with the I/O card and the process
has already been disturbed.

Under carefully controlled circumstances, this feature
enables the user to remove and insert an I/O module
without completely shutting down a running system. However,
it must be recognized that removing or
inserting an I/O module under power is potentially hazardous
to property and to personnel.

Circumstances that dictate prudent actions depend on
conditions and specific process applications at each
user facility. It is the responsibility of site personnel
to know all potential consequences of RIUP, and to
take actions to prevent all adverse consequences before
removing or inserting an I/O module under power.

Each plant or installation needs to develop guidelines for
establishing appropriate 'hot swap' procedures because

a) there are potentially lethal voltages on Terminal Boards
associated with I/O Modules.

b) each signal at each of the terminals for an I/O module
has a specific function. Any or all of the signals may be
vital for safely controlling a process.

Carl Ellis
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