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DCS Alarm Tagging Convention

DCS Alarm Tagging Convention

DCS Alarm Tagging Convention


I would like some input on correctly assigning a tag for a DCS alarm point that is associated with a bypass switch.

I have a manual bypass switch, that when placed in bypass position will be a discrete input to a PLC. I am tagging the bypass switch "HS".
When that one switch is placed in bypass position, the PLC will generate a discrete output that will be an alarm to the DCS. Note, this NOT a common alarm, only an alarm for this one switch.

1) Does the ISA standard indicate whether the DCS alarm should be an "HA", "XA", "YA" or some other "_A"?
2) Does the fact that the DCS alarm is a PLC output (as opposed to using another contact of the bypass switch) have an bearing on the tagging convention?

Thanks for your time!!!

RE: DCS Alarm Tagging Convention

1) Is this truly an alarm, or simply an indication that the switch is in bypass? If the latter, I've seen this type of thing tagged "HSI" for hand switch indication or "YS" for state of switch. I suppose if the former, "HSA" could be appropriate. However, ISA 5.1 (2009) section 2.8.2 says:


Symbols different from those given in the standard and User's choice letters when used, shall be fully described and detailed in the User/Owner's standards, guidelines, or specifications and in drawing covers sheets legends and notes.

That pretty much means to me that as long as you document what it means somewhere so someone else will know what it is, you can use it.

2) No, it doesn't, in my opinion.

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