Emerson Exchange 365

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What is act on IR?

Hey everyone,

I was wondering if someone could explain what the "Control option"  act on IR is for the bias gain/ratio blocks?

The BKCAL_IN is used for bumpless transfer, but the description in books online for act on IR sounds the same as BKCAL_IN bumpless transfer.

Am I missing something?

Thank you,

Jay

jnlevesque

• 13 Jan 2023 6:30 PM
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4 Replies

• Andre Dicaire

  

  • 13 Jan 2023 11:49 PM

  You are right that BKCAL_IN is used for Bumpless transfer, and provides the reference value and status of the downstream block. Act on IR will calculate the SP as opposed to setting OUT directly.
  
  I'm thinking that if this option is not selected, the BiasGain block would track the Output and the BIAS would be set based on the SP, and from there, the balance time would kick in? I haven't tried it. I'm sure James Beale would know...

  Andre Dicaire

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• James Beall

  

  • 14 Jan 2023 1:30 AM

  Jay,
  First, it took me years to find out that "Act on IR" means "Act on Initialization Request"! But, that is not much help. Books On Line says this:
  
  Act on IR — Used to back calculate for bumpless transfer.
  
  In the Bias/Gain function block as well as the Ratio function block, if this option is true, when the block is in a non-automatic mode or transitions to an automatic mode, the SP will be back calculated for purposes of bumpless transfer. The back calculated SP will be limited to the range defined by the SP limits. Any difference between the value required for bumpless transfer will be added to OUT and then ramped out over BAL_TIME.
  
  In the PID block, if this option is true and the STRUCTURE parameter is set to PD, then, when the block transitions to an automatic mode from a non-automatic mode the BIAS is back calculated for bumpless transfer.
  
  You will likely have to do some testing to determine exactly what it does on your case. I have never had to change this option!
  
  James

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• Trista VanDerVeeken

  

  • 14 Jan 2023 2:20 AM

  In my experience, if you require a bumpless transfer on a Bias/Gain block from a downstream module, then you need to have the "Act on IR" checked in the control options parameter.
  
  From my experience commissioning a 4 boiler system, there was 1 plant master and 4 boiler masters, in between there was a bias/gain block to handle the efficiency of the boilers, before sending the cascade input to the boiler master. 2 of the boilers were base-loaded, 1 was a swing boiler, and the other was on standby. One of the boilers tripped, the swing boiler was set to be base-loaded and the standby was brought online to be the swing boiler. The "Act on IR" was not checked on any of the B/G blocks, this caused the swing boiler to start setting the SP of the boiler master of the standby (now swing) to go from low to high (and vice versa) at a drastic rate. This caused the entire system trip.
  
  Once the "Act on IR" was checked on the swing boiler, and all scenarios were tested, the standby boiler acted as expected. My rationalization is that the PID has the integral function and the Bias/Gain or Ratio does not, so the balance time is in place of the reset function.

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• jnlevesque

  

  • 16 Jan 2023 11:50 PM

  In reply to Trista VanDerVeeken:

  Thank you everyone for your response, this helps a lot!

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