Emerson Exchange 365

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some DC Block I/Os

Hi to everyone,

i need to control a pump and a MOV by DC.

for pump i have 3 inputs as "running status", "local/remote status" and "availability alarm".

and for MOV 4 inputs as "close limit sw.", "open limit sw.", "remote availability" and "general failure sw.".

1. in state masks, how can i put these inputs as active1 or passive? it means which of them is active or passive.

2. one of my friends offered me that "remote availability" is the permissive input of DC and "general failure sw." is the interlock input. is it right?

• DC Block

Anonymous

• 3 Mar 2015 7:18 AM
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3 Replies

• gamella

  

  • 3 Mar 2015 10:31 AM

  It will be beter if you provide info about how many outputs from DC are used on the MOV and also if there is a fail-safe position defined.
  
  For MOV you can use both Active States of DC block, one for Opening and the other for Closing. Passive state will be MOV not moving at all.
  In this way "close limit sw." and "open limit sw." may be used as confirm for travel end reached on both cases (Opening and Closing).
  It could be usefult set "Passive when confirmed" in DC Device Options so output on DC will be automatically deactivated when travel end reached (almost always this is a requirement).
  Setting "Passive on Timeout " in DC Device Options depends on expected behavior but often is will be better to set it and configure long travel times.
  
  Note: Depending on what has been defined as fail-safe state for MOV this could not be valid, because DC fail state is always Passive.
  
  For that "remote availability" it depends, a permissive may be OK but if if that "remote availability" can change at anytime it will be probably better to use an Interlock.
  If "remote availability" off means that MOV is being operated locally it could be better using TRACK_IN_D to avoid improper status on DC and to follow field device status (not sure but maybe DC outputs must be intercepted before reaching DO function blocks to avoid MOV inputs being changed when it's operated locally).
  
  It seems to be OK using "general failure sw." as an Interlock, but remember, alarm will be only raised if DC was on an active state when this condiftion happens (this is OK for me....).
  
  Regards

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• Anonymous

  

  • 4 Mar 2015 7:24 AM

  In reply to gamella:

  Thanks for replying gamella,
  i have DC function on MRSS_11_IP module. because of that, i'm not sure about use Permissive or Interlock for "remote availability" or "general failure sw."!
  what's your meaning of "Passive state will be MOV not moving at all. "? does it mean the MOV will be locked?

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• gamella

  

  • 4 Mar 2015 6:24 PM

  In reply to Anonymous:

  Regarding "Passive state will be MOV not moving at all. "?, i'm supposing that a DO is activated to make MOV move to open position and a secon DO is activated to make MOV move to close position.
  Then if Active 1 is move to open position and Active 2 is move to close position then passive, both DO's deactivated, will be not move at all (hold position). Think that trying to set Close position as fail-safe on a MOV, requiring a DO to be activatec to move to close position, is not fully safe because move to close DO failure is not covered.

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