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<== Date ==> <== Thread ==>

Subject: Re: Naming Conventions and Control Logix
From: Kay-Uwe Kasemir <kasemirk@ornl.gov>
To: John Dobbins <jad@lepp.cornell.edu>
Cc: EPICS Tech-Talk <tech-talk@aps.anl.gov>
Date: Fri, 12 May 2006 12:22:57 -0400
Hi:

If you use the EtherIP driver, see
  http://ics-web1.sns.ornl.gov/~kasemir/etherip/index.html
you'll notice that it's much more efficient for it
to access array tags.
I just noticed that Bob beat me in stating this ;-)

So the situation is typically like this:
You might have records with great looking names like
  ThingyXY1_Voltage
and
  ThingyXY1_Current
which both read data from PLC tags.

Those PLC tags, however, are meaningless array tags like
  ANA_XFER_RD[10]
and
  ANA_XFER_RD[11]
Well, the only meaning is:
ANA_XFER_RD=analog data transfer array, meant to be read by IOC.

To beautify your PLC code, you can create aliases in RSLogix:
  ThingyXY1_Voltage = alias for ANA_XFER_RD[10]
  ThingyXY1_Current = alias for ANA_XFER_RD[11].
That way, you have somewhat readable ladder logic,
while the data still resides in the array elements,
and can be transferred in a single array 'read' request.

Now one could rephrase your question as:
How well do your alias tags and the EPICS record names match?

In the systems that I've been somewhat involved with,
they didn't because
a) There were several instances of the same PLC code,
   duplicated on different PLCs.
   So on each PLC, you'll find the same tag names,
   but of course their associated EPICS record names
   needed to be unique.
b) The PLC programmer was free to pick any names.
   The only interface with him were the transfer array names,
   which of course don't carry any signal meaning.

-Kay



On May 12, 2006, at 12:04 , John Dobbins wrote:

ControlLogix Users,

I am wondering what folks do about ControlLogix Tag names when it comes to naming conventions.

1) As I understand it ControlLogix Tags names may contain underscores, letters, and numbers. Most naming systems include other separators such as hyphens, colons, periods. So what happens when these two meet?

2) Many times a ControlLogix tag has a corresponding EPICS database record. How do you distinguish these names, i.e. the Record name and the Tag name? Or are they the same and distinguished by context?

Thanks,

John Dobbins
Lab for Elementary Particle Physics
Cornell University




References:
Naming Conventions and Control Logix John Dobbins

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