Anyone has a formal definition of what a "Complex Loop" is in contrast to a simple "Instrument Loop"? To me a complex loop is a comination of two or more instrument loops. Please help; i was asked this question and was not able to come out with a formal definition.

 

Interesting question. I'm not sure it has a definition. When I hear the term, I ask, "what do you mean by complex?"

In general use, the term is used for control loops above and beyond the simple single input, PID or on/off, single output loops; for instance, complex control is used for cascade control, feed forward, ratio control or the use auxiliary signals. Or multivariable control.

David

 

Definition of complex loop, any loop that the functionality and logic can not be ascertained looking at conventional documentation i.e.: P&ID's Loop sheets. That's how I define, our organization has multiple definitions from site to site engineer to engineer. I try to keep it simple. What we do require of a "complex loop" is a logic narrative along with printout of the logic in the loop folders for sell off and for projects we require a separate binder for all complex loops each individually numbered. Additionally we require delivery of them to site QA or inspector 1 month or greater prior to FAT (Factory Acceptance Test).

good luck,
Burt

 

Definition of complex loop, any loop that the functionality and logic can not be ascertained looking at conventional documentation i.e.: P&ID's Loop sheets. That's how I define, our organization has multiple definitions from site to site engineer to engineer. I try to keep it simple. What we do require of a "complex loop" is a logic narrative along with printout of the logic in the loop folders for sell off and for projects we require a separate binder for all complex loops each individually numbered. Additionally we require delivery of them to site QA or inspector 1 month or greater prior to FAT (Factory Acceptance Test).

good luck,
Burt

Very helpful. We had an ABB analyzer whose output we had to freeze in the DCS upon activation of a digital signal for 720 seconds. The DI was for flushing the sample system. Logic can't be captured by conventional documentation. Complex Loop.

 

That's the sort of question asked by someone who doesn't understand the complexity of automation involving interface with separate systems such as analyzers.

 

That's the sort of question asked by someone who doesn't understand the complexity of automation involving interface with separate systems such as analyzers.

Agreed. The purpose of the question was to elicit a formal definition from the responder - not to enhance the understanding.