2 replies to this topic

[shahidulislam48]

Hi,

 

I have some queries. Would be happy to get suggestion.

 

1)In a process line, I have a FT and Air-To-Open (FC-Fail-To-Close) Control Valve. If the flow through the FT tends to increase until it reaches set point, the controller output (%CO) also increases (flow has to increase to reach set point) as the control valve is Fail-To-Close. Hence the control action is Direct Acting.

 

If flow becomes higher than set point, the controller output (%CO) decreases to decrease flow to set point. Hence controller output decreases as input signal increases which leads the control action to be Reverse Acting. (Page-196-8.3.2-Process Dynamics and Control, 2^nd Edition by Dale E. Seborg)

 

In this case which one is right, is the control action Direct Acting or Reverse Acting?

 

2)Is it always true for heat exchanger, whether it is cooling or heating purposes, whether the control valve is fail-to-open or fail-to-close, the control action is reverse acting?

 

Thanks for giving your concern.

 

Shahidul Islam

[Bobby Strain]

This is a basic definition for control. You should look at the basics, and you may learn even more.

 

You can find all you need here.  http://www.pc-education.mcmaster.ca/

 

Start here. https://en.wikipedia...=PID_controller

 

Bobby

Edited by Bobby Strain, 12 July 2017 - 10:46 AM.

[shahidulislam48]

Thank you Sir Bobby Strain for your reference.