Emerson Exchange 365

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OUT SCALE of PID Block

Hi Everyone,

I was trying to change the outscale of a PID block using the ACT(IND=1). When PID block IN input is not connected then i am able to change the outscale. But when i will connect IN the input to the PID , ACT( Action block) shows an output error & outscale come to default values.

Action Block syntax i have written is( '/PID/out_scale.EU100':='//FIC-1558/AI1/Out.CV) 

Thank you,

Rajeev Kumar

• 17 Feb 2018 3:58 AM
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5 Replies

• Roman Kostuniak

  

  • 17 Feb 2018 4:17 AM

  Not happy.
  1. This is master in cascade loop? Are you using here bypass?
  2. You should use better 2 PIDs for different scales.
  3. You should change PV_SCALE (AI!)
  4. What is the scale when act/in_d = 0?
  5. Remember (check) about out_hi_lim / lo_lim OR if you change PV_SCALE : sp_hi_lim, sp_lo_lim.

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• gamella

  

  • 17 Feb 2018 7:30 AM

  What's the functional purpose of doing that OUT scale change in run-time?.
  Out scale is a configuration parameter not suitable for run-time change. Changing it during run-time may require changing PID to OOS mode first, then change scale and lastly change mode back to previous mode.
  Note that if OUT scale change on the fly were allowed directly, this will generate a kick into OUT that will propagate into slave block (an AO, another PID, etc...). Changing PID to OOS will make slave to go IMAN and then out scale change kick is not propagated directly to slave.

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• Rajeev Kumar

  

  • 17 Feb 2018 3:43 PM

  In reply to gamella:

  I am using this for RCAS mode. When i keep Target mode Auto & normal mode Man then outscale range works well('/PID/out_scale.EU100':='//FIC-1558/AI1/Out.CV) as i required. This is because in control option there is one option (No out limits in manual). When i changes the normal mode to auto or Rcas outscale freeze to its last value. Is there any way to write no out limits for RCAS & Auto mode.

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• Matt Stoner

  

  • 19 Feb 2018 11:44 AM

  In reply to Rajeev Kumar:

  The Normal Mode has no effect on the control of the PID block, it is just used to indicate when the Target/Actual modes are not equal to the configured Normal Mode.
  
  RCAS mode is like AUTO mode in that it controls to a "SP" (RCAS_IN parameter of the PID Block) which manipulates the OUT parameter based on how PV relates to the SP.
  
  What is the Status of the RCAS_IN parameter? If you don't have anything wired to this parameter then my guess is that it is still the default BadNotConnected. Change this default status to GoodNonCascade and it will start to modulate the OUT to control to the SP value in the RCAS_IN parameter.

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• James Beall

  

  • 19 Feb 2018 1:37 PM

  In reply to Matt Stoner:

  Rajeev,
  I share the earlier concern about changing the OUT_SCALE. Note that the PID works in "%PV" and "%OUT", so if the OUT_SCALE changes, the loop gain will likely change. In addition, to OUT limits, the ARW limits would likely need to be changed if you change the OUT_SCALE. If you are switching to different "slave devices" (e.g. PID or AO's) with different units, there may be better alternatives, depending on what you are trying to accomplish. Note that if you are using the "Bypass" feature on the secondary cascade loop, it is expecting a SP (CAS or RCAS) that has the same scale as its PV_SCALE. If this is still an issue, please elaborate on what you are trying to accomplish.
  James

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