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Dual Process Input For Control Valve Positioning / Regulating

control valve process controls pressure control oxygen monitor tank blanketing

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#1 ShannonG

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Posted 30 June 2016 - 03:39 PM

I am trying to set up a control system for a tank that is blanketed with a hydrocarbon gas (vs. inert gas).  In order to improve the safety of the operation of the tank, I was thinking I would initially control the system with an oxygen analyzer linked to the blanketing control valve.  Control valve would use the oxygen value and control purge / blanket gas to keep below a certain set point.  In addition, to minimize potential of over-pressuring the tank, I was wondering if it's possible to also use a pressure input that would 'override' the oxygen sensor control and limit the control valve opening?  In essence, a bit of 'dual' control - is this possible, how is it done (PLC logic?) and does anyone have experience with this type of control system?

 

Thanks in advance!
Shannon



#2 shvet

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Posted 30 June 2016 - 10:46 PM

  I was wondering if it's possible to also use a pressure input that would 'override' the oxygen sensor control and limit the control valve opening? 

 

Example of such control loop.



#3 cea

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Posted 01 July 2016 - 12:06 AM

Not a tangible idea.

 

Firstly please note that any such sample analyzers are not very accurate to use it for control loop. Secondly, the reading is run time value, which may differ from bulk reading. And lastly, the parameters that you are trying to consider, are totally different, such as O2 % & pressure. It is very difficult to configure such loop.

 

The traditional practice is to keep this control loop on pressure only with periodical sampling. This is proven practice & do not have any loop holes.






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