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Old October 7th, 2008, 01:34 AM
jberge jberge is offline
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Join Date: Dec 2003
Posts: 278
Actually I think "back up control in case of host failure" is probably rare. I have never seen it.

Control in the field (CIF) is used in its own right, as a primary means of control, not just as a fallback. It is that reliable. Many plants use this concept.

Cascade loops are common for CIF and easy to do. Although there is a standard ratio block, I have not seen it. However, I have seen ratio CIF using the standard arithmetics block to compute the setpoint.

But true, CIF is not for every loop. There are some loops that cross multiple buses, or use inputs or outputs that are conventional or come from other bus technologies etc.
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