RSLogix5000 Alias Tags

I'm working on a project that was converted from RSLogix500 to RSLogix5000. The converted RSLogix5000 program has most of the Tags setup using Alias's referencing the RSLogix500 data format such as B3:0/0, etc. I'm going through the program giving all of these tags descriptive names, while leaving the alias in place. My question is, would it be best to remove the alias and go back to a base tag. I've read that the alias tags can get jumbled on an upload if you don't have the orginal project file. I believe the primary reason the tags where all set up with RSLogix 500 aliases was to make the program conversion easier.

I'm going to alias the I/O and fault routine bits, that part I understand, I'm just not quite sure what the ramifications of changing an alias tag back to base tags is (I'm talking over 200 tags). At this point I'm not even sure if it's worth doing. Any thoughts or suggestions would be greatly appreciated.

The "jumbled up" issue you're describing is when you use more than one level of aliasing.

For example:

"Tank_Level_High_Indicator" is an alias for "Pilot_Light_2".
"Pilot_Light_2" is an alias for "Local:O.Data[3]".

If you were to upload this project without having the offline file available, you would find that "Tank_Level_High_Indicator" would appear as an alias of "Local:O.Data[3]". The intermediate Alias level would not appear, because it was eliminated during compiling of the project during download.

Multi-level aliasing is uncommon, and I don't think it will be a problem for you in this system that sounds like it converted SLC "Symbols" into ControlLogix "Alias Tags".

Awesome thanks Ken,I must say you know your control's. One more question, If I decided to change an alias tag back to a base tag, would I need to create a new tag or can this simply be done in the edit tag properties dialog box?

Ken Roach said:

The "jumbled up" issue you're describing is when you use more than one level of aliasing.

For example:

"Tank_Level_High_Indicator" is an alias for "Pilot_Light_2".
"Pilot_Light_2" is an alias for "Local:O.Data[3]".

If you were to upload this project without having the offline file available, you would find that "Tank_Level_High_Indicator" would appear as an alias of "Local:O.Data[3]". The intermediate Alias level would not appear, because it was eliminated during compiling of the project during download.

Multi-level aliasing is uncommon, and I don't think it will be a problem for you in this system that sounds like it converted SLC "Symbols" into ControlLogix "Alias Tags".

Click to expand...

I learn something new everyday. I guess I never ran into this because I never had a situation were I would use more than one level of alias tags. Is there a technote on this behavor?

I don't know the KB but there is one. I learned this lesson from my predecessor the hard way.

Sorry, I don't follow want your saying. Are you saying you had issues changing alias tags back to base tags.

Originally posted by The PLC Kid:

I learned this lesson from my predecessor the hard way.

Click to expand...

Talk about the perfect storm!!

How did you get bit by this? I can think of a possible scenario but I would be interested how it hit you.


Keith

Ken Roach said:

The "jumbled up" issue you're describing is when you use more than one level of aliasing.

For example:

"Tank_Level_High_Indicator" is an alias for "Pilot_Light_2".
"Pilot_Light_2" is an alias for "Local:O.Data[3]".

If you were to upload this project without having the offline file available, you would find that "Tank_Level_High_Indicator" would appear as an alias of "Local:O.Data[3]". The intermediate Alias level would not appear, because it was eliminated during compiling of the project during download.

Multi-level aliasing is uncommon, and I don't think it will be a problem for you in this system that sounds like it converted SLC "Symbols" into ControlLogix "Alias Tags".

Click to expand...

Ken's statement is not 100% correct. It is not always the intermediate alias tag that will "disappear", sometimes it is the "outer" tag. It appears as though the system will use the first tag it finds in the database (alpha-numerically speaking).

Refer to the pictures for a practical example of this.

I programmed a rung with all three levels of tag addressing : the base tag, an alias to it, and an alias to the alias ** : see pictures Alias1.jpg and Alias2.jpg

** note : RSLogix displays the base tag, not what the tag is an alias for - Alias2.jpg shows this clearly in the tooltip.

I then went offline, and immediately did an upload - Alias3.jpg is what the rung looked liked after. Notice that the references in the logic have changed, and they all refer to First_Level_Alias (which is equivalent to Ken's Intermediate tag).

Well I was a bit surprised by this, as I had always thought that what Ken said was the case, so I put the code back as it was in Alias1 and Alias2 pictures.

I then renamed Second_Level_Alias to Alias_Second_Level, thus making it alphanumerically above First_Level_Alias. See Alias4.jpg

I then went offline again, and did another upload - Alias5.jpg is what I got back.

You can clearly see it has now replaced all the references to the first alpha-num alias.

.....continued from previous post......

Note that the aliases that "disappear" do not get deleted from the database, even though they are not referenced in the code anywhere - Alias6.jpg shows the tags in the database after I had finished.

And all that got me thinking about another issue to do with using aliases, and that is what happens when two or more alias tags are aliases for the same base tag - as I have shown in Alias7.jpg

Well, after an upload, it does the same thing, replacing references in the code to the first alph-numerical alias tag it finds, as Alias8.jpg shows

All very interesting
I am wondering about communications
Base with Alias1 and Alias2
HMI1 - Connects to Alias1
HMI2 - Connects to Alias2

What happens on an upload download? do we loose an alias? is HMI2 broken?


*** Edit Daba may have just answered my Question - Alias is there just not used in the Ladder logic

To complete the story, I have used Ken's tag-names - see picture Alias9.jpg

After an upload, Alias10.jpg is what you get, because "Pilot...." is above "Tank.....", alphanumerically.


I suppose so long as you understand what the system does to your code when you upload, it isn't really a great problem.

And it doesn't stop you finding the places in the code where you used the original tag-names either, because, as always, cross-reference is your friend......

In the last example, Tank_Level_High_Indicator is no longer referenced in the code, but if you were to cross-reference it in the database, you will see that it "finds" the reference to Pilot_Light_2, and tells you where it is used (See Alias11.jpg)

MichaelG said:

All very interesting
I am wondering about communications
Base with Alias1 and Alias2
HMI1 - Connects to Alias1
HMI2 - Connects to Alias2

What happens on an upload download? do we loose an alias? is HMI2 broken?


*** Edit Daba may have just answered my Question - Alias is there just not used in the Ladder logic

Click to expand...

Yes, the unused alias tag (whichever it is) will still be there, and of course it references the data in the base tag, so everything should still work......

....however, if you were to do a clean-up, i.e. deleting "Unused" tags... !!!!