Help for Boiler 3 element control

I am implementing boiler 3 element control on Compact logix..
can any body tell explain me control philosophy
when three element is selected then single element should be in manual mode and when i move back from 3 element to single element then i need to make it bump-less but i could not make it
can any one tell me how we can make it.....

Not quite sure what you are trying to do.

Usually when I have 2 or 3 element boilers, I add separate start and stop setpoints for each element, with the possibility to disable each element.

I have found out that it is good to KISS in these cases.

Ali Raza said:

I am implementing boiler 3 element control on Compact logix..
can any body tell explain me control philosophy
when three element is selected then single element should be in manual mode and when i move back from 3 element to single element then i need to make it bump-less but i could not make it
can any one tell me how we can make it.....

Click to expand...

Described simply, three element feedwater (drum level control) involves cascaded loops with the Level Loop providing the setpoint for the feedwater loop. The steam flow value is best applied to the level loop output.

In my opinion, 3 element feedwater is extreme overkill in 99% or more of applications. If you really need 3 element, and don't understand how to make cascaded loops work, then you are going to have a difficult time making the control scheme work and tuning it properly.

I hope you don't take offense at my directness. I have done boiler drum level control many, many times and the only times I have had to do 3 element was when some engineer fresh out of university forced the issue. It was not required by the application.

Yes, it is occasionally helpful in controlling the drum level, but it is so rare, I would suggest trying two element first.

JHarbin, now you have me interested. Could you tell me what two/three element feed water is?

I assumed you the OP was talking about simple heating elements inside a boiler (calorifier).

EDIT: http://controlguru.com/cascade-feed-forward-and-boiler-level-control/

Never knew there was a name for this .