ControlLogix Tagname Rant

DonnyB · Feb 28, 2007

I’d like to know how are others are handling tagnames in ControlLogix 5000s. My experience is rather limited in this area.

Yesterday I worked on a program that had a tag named CHW_FCV9401A_NMP.Max_Flow_Parameter_Default (that folks, is 43 characters long). Heck that is a sentence not a name. They routinely use tag names of 30 characters or more and then leave the descriptor field completely blank.

Aren’t tag names primarily just a replacement for addressing? Now imagine trying to talk about that “address” over a radio or phone call to someone, let alone type it into the program accurately repeatedly.

When Rockwell started using the symbol feature way back with their IPDS software you were limited to about 8 characters and many would use the I/O device name there: PS803, SOL456, FT1000, etc. Descriptors were maybe 5 lines X 20 characters, which was usually sufficient. If you wanted, you were able to program by typing in either the symbol name or address.

I understand SOME of the advantages of the ControlLogix tagname structure but is a 43 character tagname/address really an improvement? What are some of ideas on tagnaming conventions? Anything but 43 CHARACTERS…………….YUK!!!!!!!!!!!!!

CroCop · Feb 28, 2007

South_Trolley_South_Enable is typical of something I do. I always relate it to the real world function, but I haven't done any super high IO projects.

TheBigHarv · Mar 1, 2007

DonnyB,
Agreed, 43 characters is a little much. That program would be hell to follow if you had a small screen on your laptop.

When we do big projects we always break the lines down into Station #'s (ST###_) then a short description of what tooling we are using like a valve (VLV_#) followed by the action of that tooling (EXT or RET). So in the end you have "ST40_VLV_3_EXT" I've found it pretty easy to follow and our maintenance guys find it good for trouble shooting. They aren't allowed to make edits but they can look through the program on the line terminals and see what is holding a station up.

curlyandshemp · Mar 1, 2007

Since tagnames reside in the PLC's memory, long tagnames consume more memory than shorter ones. Another reason to use smaller tagnames. I always like to use tagname descriptions and rung comments.

Ian

dash · Mar 1, 2007

"CHW_FCV9401A_NMP.Max_Flow_Parameter_Default"

Hmmmm.... that kind of looks like a York chiller tag. CHW always makes me think of chilled water, but it is actually something else that escapes me right now. The FCV9401A is the control valve tag you can find on the P&ID and the valve tag on the equipment. Have no clue what the NMP is and the UDT elements do seem a little wordy. Unless it is causing a readability issue with the ladder not wanting to wrap correctly to me it is fairly good. The program would be readable even if you did an upload from a processor and did not have the tag/ladder comments.

Just my opinion,

Darren

Forgot to mention that I like the CHW prefix since that all the areas devices are grouped when you sort by name in the tag browser. When you have flow control valves, thermocouples, etc I dislike having only the device ID. I would never remember where the FCV9401A is, but with a prefix for the area it helps.

rdrast · Mar 1, 2007

With the auto-complete feature in the editor, as well as the ability to pick from a list, I would much prefer long, descriptive tag names to something short and meaningless.

Yes, tags are stored in the PLC, but you would have to get excessive to tax available memory.

And, it's good that the tagnames are stored in the PLC. Using a decent, descriptive tagname will assure that they program is documented to some degree at least.

I generally organize everything into UDT's, which are generally multi-level. I have no problem with a tag such as "Capstan.Setpoint.REF_Coord_Speed".

dskohio · Mar 1, 2007

Tagname Length

The nice thing about the tagnames is that they stay with the controller, so even if someone modifies code, you will have some idea what the tag does if you don't have the latest project file.

As for length, the programs I have some tags that are really long. What really becomes fun is using array indexes and bit numbers dynamic using other tagnames. For example

array1[index1].[index2]

One example I have uses 20 characters for array1, 37 characters for index1, and 40 characters for index2. Include the required brackets, and the total tag length is 102 characters.

You don't know how happy I was when I got my widescreen laptop for use in the field, and a second monitor for use in the office.

Black Jack · Mar 1, 2007

curlyandshemp said:
Ian

I have found using the UDT (user defined data type) as Curly displays above reduces tag name length considerably. UDTs can be set up for VFDs, valve and motor control, recipes, PID control, and generally anything that uses a repeatable set of data. Then I just set up a tag that uses that UDT for a data type (typically the device tag or loop tag).

I also am a firm believer in address comments...once they are set up in the UDT, they follow the new tag and you don't have to type them in individually. I have found long tag names are usually used by programmers who don't like to use address comments.

Just my $.02.

russrmartin · Mar 5, 2007

Standards

Having tagnames is a huge benefit, or detriment. You need to get a handle on it right away. When we decided to go with the CLX5000 platform, we created a list of programming standards. A huge part of this was tagname format. We decided to go with a 16 character max, with program tags being small case, controller scoped being ALL CAPS. We also state that program tags are to be avoided as much as possible, and that descriptions are required on all tags. This system is not perfect, but it has helped protect against the 43 character tags.

darrenj · Mar 5, 2007

dash said:
"CHW_FCV9401A_NMP.Max_Flow_Parameter_Default"

Hmmmm.... that kind of looks like a York chiller tag. CHW always makes me think of chilled water, but it is actually something else that escapes me right now. The FCV9401A is the control valve tag you can find on the P&ID and the valve tag on the equipment. Have no clue what the NMP is and the UDT elements do seem a little wordy. Unless it is causing a readability issue with the ladder not wanting to wrap correctly to me it is fairly good. The program would be readable even if you did an upload from a processor and did not have the tag/ladder comments.

Just my opinion,

Darren

Forgot to mention that I like the CHW prefix since that all the areas devices are grouped when you sort by name in the tag browser. When you have flow control valves, thermocouples, etc I dislike having only the device ID. I would never remember where the FCV9401A is, but with a prefix for the area it helps.

Like Dash said i like the long descriptions, Without even knowing the program or process i understood at once you were talking about a chilled water valve and the max flow allowed.

better than the stuff i deal with .."LSB101"..now i know its a limit switch but what does it do? where is it? and what machine is it on!!..while i like rung comments and descriptions, there are pleanty of people who dont use them..makes it hard for us "bubbas" to figure out.

Darren

Alan Case · Mar 5, 2007

Hi Russ. We are the other way, the majority of the tags are program tags, controller tags are only added when you need a global scope.
Regards Alan Case

kamenges · Mar 5, 2007

Originally posted by Black Jack:

I also am a firm believer in address comments...once they are set up in the UDT, they follow the new tag and you don't have to type them in individually.

That isn't a universal thing. I THINK this really started to work with version 13 or so. I look through some version 10 stuff on occasion where this is definitely not the case.

Like Alan Case, we use controller level tags only when we need them, although we don't have much reason to. Our programs are typically only set up with a single program, so the distinction doesn't mean much unless you are talking about an HMI. It's just the way we have mutated.

When russrmartin mentioned tagname format I thought he was going to talk about naming convention, not baseline restrictions. We try to name our tags in a top-down manner. Something like <section>_<component>_<attribute> or some such. While the tagnames can get long, they actually mean something and you can find them in a hurry. They are self-sorting.

Keith

lifepreserverplease · May 4, 2007

Tag names should be kept short for another reason, if all your tagnames are 75 characters, you can only see a handful of instructions as you view the program before you have to scroll sideways.

edited
however, i do like the long tag names when no original copy of the acd is available and you have to rely on an upload, then the long tags are a godsend.

Mpoon · May 4, 2007

Yes or no. Advantage or disadvantage. It all depend on user's preference, some one like, alse don't

There is a room for an improvement for Rockwell Software. for example, choice of display long tag name all time, or Tag can be hidden away, only shows up whenever mouse is landed onto the ladder's instructions.

ControlLogix Tagname Rant

DonnyB

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CroCop

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TheBigHarv

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curlyandshemp

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dash

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rdrast

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dskohio

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Black Jack

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kamenges

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lifepreserverplease

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Mpoon

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