P&ID Tag Numbers in PLC I/O Address Symbols?

Joel777

Member
J
Join Date
Oct 2013
Location
Texas
Posts
4
Folks out there with PLC process control experience, how common is it to see -- and to request as the customer/system specifier -- P&ID tag numbers embedded in the I/O symbolic address descriptors? For instance, let's say an analog input receives a signal from a temperature transmitter identified on the P&ID as "TT 301" and physically located at the north side cooling coil. Regardless of the PLC brand and unique address identifier, I might give it a symbolic descriptor "TT301 North Cooling Coil". I know I've seen this before, but is it common and reasonable to expect? If not, how do you typically maintain a coherent, logical connection between P&ID tags and PLC I/O lists?
Thanks in advance.
 
Personally, I think the P&ID numbers (or wire numbers) should be in the comments, at a minimum, but in the tag name might be better. I've heard some debate about whether the number should be before or after the descriptor in the symbolic name. Good arguments both ways, really boils down to personal preference.

I'd say it probably isn't universal, but is at least fairly common.
 
A few sites that I have seen use AOIs to process instrument signals and perform scaling. The tag name follows the site tagging standard such as "ISAAcronym_Area#_Tag#." This matches, except for the underscore instead of the hyphen, all of the other electrical and instrument drawings. The only thing that doesn't quite work is equipment start/stop/interlock/permissive tags, but that is handled by using a tag such as "P_44_3301ST" (area 44 pump 3301 start).
 
I like to use P&ID Tags as my Program Tags. In the comments I will put the other descriptive info like "Pump Start" or "ESD Horn". To me it just helps the plant personnel if they have to do any work on the system. Plus it helps me out later on when I forget how the system works. I can just look at the P&ID and get up to speed pretty quickly.
 
My experience, the P&ID identifiers ARE the PLC tag. No more, no less.

I always use AOIs for device control as I can derive/create much more information or functionality by doing so. In your example, my AOI would have the following members:

Code: 
TT301.rawData
TT301.rawMin
TT301.rawMax
TT301.engMin
TT301.engMax
TT301.scaledValue
TT301.simMode
TT301.simValue
TT301.error

The base "TT301" tag would have a simple description "North Cooling Coil Temperature Transmitter". So all the tag members would have that basic descriptor, and append the descriptor of the AOI member definition.

Code: 
TT301.rawMin         "North Cooling Coil Temperature Transmitter - Raw Scale Minimum"
TT301.rawMax        "North Cooling Coil Temperature Transmitter - Raw Scale Maximum"
TT301.engMin         "North Cooling Coil Temperature Transmitter - Eng Scale Minmum"
TT301.engMax        "North Cooling Coil Temperature Transmitter - Eng Scale Maximum"
TT301.scaledValue  "North Cooling Coil Temperature Transmitter - Scaled Value"
TT301.simMode      "North Cooling Coil Temperature Transmitter - Simulation Mode"
TT301.simValue      "North Cooling Coil Temperature Transmitter - Simulated Value"
TT301.error            "North Cooling Coil Temperature Transmitter - Transmitter Error"

Note, I would make an adjustment to the raw data member to include the physical IO

Code: 
TT301.rawData        "North Cooling Coil Temperature Transmitter - Analog Raw Input Data (C01S02/01)"

In this example, "C01S02/01" is a chassis identifier I use. "Chassis #01, Slot #02, channel #01". This would be the wire label, and identifier on the Electrical prints. The electrical print descriptor would match the AOI tag "TT301 North Coiling Tempurature Transmitter".
 
For re-usability of code, not having the tag names allows better consistancy. You would then use a printed I/O schedule to determine which input was associated with which P&ID Tag. For what I consider one off process control systems, I have only ever seen P&ID Tags based addressing, but for some PLCs that comes with a particular OEM equipment like a heater, where they sell the same heater to several different plants, I have seen them not use P&ID Tag addressing.
 
It certainly makes troubleshooting easier if the PLC descriptor matches or is at least very close to matching the description on the drawings.

I can't count the number of times issues have arisen because the programmer thought the electrician was connecting or disconnecting a different device than they were programming.

And finally, make sure someone updates the drawings and the end user gets a copy of the PLC program with the descriptors.
 

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