Program Tags - do your systems use these?
ControlLogix and CompactLogix projects are capable of holding more than one "program" - and each program has its own independent set of tags. This gives a programmer a great deal of flexibility - especially when developing the types of systems which control several identical pieces of equipment.
In simplest terms, once the first program has been written and debugged, it can then easily be copied and pasted into place for each of the remaining pieces of equipment. Since each piece of equipment is allowed to have its own independent tag listing, the tagnames can be identical from one program to the next.
The basic idea behind this arrangement is referred to as assigning each tag a certain "Scope" when the tag is first created. A tag which is scoped at one particular program's level will not be accessible to any other programs.
While this approach gives the programmer a lot of power and flexibility, it can be quite challenging to the maintenance technicians while troubleshooting a problem. Since it's possible to have one - two - three - or even more tags all named "Run_Relay" it is quite common to see untrained technicians waste expensive downtime while chasing after the wrong tag.
Understanding how tags are "scoped" is a critically important job skill for technicians, so our classes have plenty of hands-on exercises to bring you up to speed on how to deal with these issues in real-world situations.
Reference material on Allen-Bradley's website - Page 27 [Adobe page 29 of 90]
© Copyright - R.H.Beaufort - Charleston, SC – Updated: November 15, 2013