Emerson Exchange 365

PV for BKCAL_OUT set on cascade loop

I was checking several Master - Slave loops from the plant and found that "Dynamic Reset Limit" is checked on Master but "Use PV for BKCAL_OUT" is not in cascade. I was reading about that recommendation but couldn't get the benefits having this configuration or what this can improved? Is it possible somebody could clarify this configuration?

Thanks!

Maria I.

Maria Portillo

• 24 Jun 2016 12:28 PM
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1 Reply

• HECTOR H. TORRES

  

  • 24 Jun 2016 5:40 PM

  Hola Maria, the BKCAL_OUT in the slave loop by default sends the SP value to the BKCAL_IN of the master. If you do not change this to Use PV for BKCAL_OUT the setpoint is being sent back and the dynamic reset limit will not be working as it should.
  
  By enabling the PV for BKCAL_OUT, the PV in the secondary or slave loop plays the role of the external-reset feedback. The dynamic reset limit will then avoid the master's controller output to change faster than the slave's %PV can respond. In all cases of cascade control, this dynamic reset limit can enable the primary loop to be tuned for best disturbance rejection; fastest response; without worrying about the consequences of a secondary loop not being able to keep up with the changing demands from the primary loop. The only requirement is to have integral action configured in the secondary controller so that the primary’s %CO and %PVs are equal in steady state.
  
  Hope this helps.
  Héctor

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