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Reverse Or Direct Action In The Pid Controller, And The

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#1 titim


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Posted 25 May 2016 - 02:13 PM

hi everybody, i don't know if i'm in the right forum, but you can suggest me, in need to know how i can select Reverse or direct action in the PID controller ( in simulation or real life, and what is meaning (action on the regulator at the controle room)

ex;: we have in our refinery some PID in reverse action like showed in picture (general loop) the drum 100-d-101 that is commanded by a regulater (ABB commander 500 in the controle room). why:

1- Why in (ABB commander 500) is totaly closed at 100% and opened at 0%
(100% on the commmande means 0% opened  on the valve,
and 0% on the commande means the valve is at 100% opened)

2- what is the slave and the master (level or flow : LC or FC)

NB at the controle room the ABB commander 500 is named  FRC 107,

the inlet of the drum come from the crude distillation column ( overhead) and the liquide (bottom of the drum go to the dubutaniser column

thank you a lot

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#2 Hassan seif

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Posted 25 May 2016 - 03:53 PM

hey there

one possible cause for the reverse action of the ABB 500 is for power failure mode required for example if there is a power failure and commander 500 output is zero then the valve would be 100% opened maybe thats what the process engineer need

from your sketch the level controlller is the master and flow controller is the slave

i hope that i helped


#3 Bobby Strain

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Posted 25 May 2016 - 09:45 PM

You can have it any way you like. Because you can select valve positioners as direct or reverse acting. The control valve position on air failure should be to the safest position. In my opinion control valves should fail closed unless there is good reason to do otherwise.


Probably master and slave are not good terminology. An appropriate description of the controls shown are flow control reset by level control. This is quite clear to almost anyone.



Edited by Bobby Strain, 25 May 2016 - 09:48 PM.

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