Rung Comments?

Today I was looking at a program with 175 rungs. Not one had any type of comments. The bits were all identified. I was wondering how many actually provide rung comments and why you do or do not.

Your poll question is 'Do you use rung comments?'

I answered 'sometimes', the reason I gave that answer is because it will all depend what I am doing.

I will explain further....

I do not work for an OEM, I work in a container port and the majority of my PLC work is upgrades and modifications. In this case the process is well known by the technicians, the names assigned to the I/O and flags are also well known, so in this case no rung comments are required. Occasionally, I will be tasked with 'ripping' out old control systems (not PLC) and replacing them with a brand spanking new S7, in this case I do comment rungs, mainly for myself than anyone else because I am never allowed to complete one project before starting the next, I always have to have two or three on the go at the same time... Apparently priorities change.

Paul

P.S You'll upset Casey by posting this poll

I answered sometimes because if I have several rungs that concern one operation, I will only comment the first rung.
Example:
This logic will open the charging valve until the desired weight is obtained.

I answered "Always", My Job Role is very similar to PLucas, But spread over 3 facilities. As the plants manufacture 24 hours a day then that little bit more information can be the difference between a good nights sleep or a midnight drive. However im trying to apply the philosophy that if the HMI Diagnostics are good enough then you shouldnt need to go Online! still alot of convincing needed to our Management Team to justify additional Time & Cost.

12 months untouched down the line you'll be glad of the extra documenting of the code.

Steve

stevo said:

12 months untouched down the line you'll be glad of the extra documenting of the code.

Click to expand...

Precisely...

and even then, despite the commenting, I still have to ask "What the hell was I thinking?"

Originally Posted by Alaric
"What the hell was I thinking?"

Click to expand...

Not Just me then!

Steve

I always use rung comments, though I admit they're not always as 'descriptive' as I'd like...



-Eric

I don't add comments that simply restate what can be read in the line of logic. My comments are aimed at helping the reader understand what's being done if it's not clear, or why something is programmed a certain way. I use them to write out in enlgish the formulas used in complex math instructions with an explanation for each argument. I also use them to identify modifications and date and initial changes. Later, I can search for my intitials in the comments to find the rungs I have changed. I use page titles in RSLogix to help separate the logic into related groups, and rung comments for items within the group. That makes advanced diagnostics (CTRL+D) work really well.

Hmm...

I answered always, however, not on EVERY rung... I think the use of page headers and rung titles are also very good trouble shooting tools... For example in RSLogix if you go to "Search" then "Advanced Diagnostics" you will see a great aid in finding sections of code, but only if they used Rung Titles to group their logic...

Always and every rung. Even if it's something simple.

I comment my rungs with a title, description, and date. In some cases where the logic is easy to read I'll just put the title and date. When I have several rungs used for one operation all the rungs have the same title.

e.g.

Pump 1 Failed To Start
This rung sets up the failed to start delay.
08/02/05

Pump 1 Failed To Start
This rung sets the failed to start alarm after a 10 second delay.
08/02/05

Pump 1 Failed To Start
08/02/05

I voted 'Yes, always', but that doesn't mean I do use rung comments on every rung. It only means I do use rung comments in every program I write. I don't think, just like Ken said, that it's necessary do comment every rung. I also agree on the statement by OkiePC that it is not usefull to simply restate in the comment what the logic is doing. But clarifying why the logic is written that way, and aiding in speeding up the interpretation of the rung logic is definitely my aim when commenting. And I like the option Daniel mentioned. Unfortunately not every package allows for this.

Kind regards,

Like several others, I always comment my rungs, though not always EVERY single rung.

I also use them to describe what is happening & why, as well as to date and initial changes.

Marc

As with the majority I always comment as much as possible to give the following person a good idea as to what the system is doing.
What is frustrating is when you find the program that you worked on ages ago has been uploaded from the plc nd saved in such a way that the comments are wiped so you end up with "comment" and nothing else all I can say is thank god for my archives.

Always, almost every rung (where it's not pointless anyway.

I work for an OEM and there have been more than enough times where I've had a customer calling me and it takes me too long to get up to speed on what he's saying. By reading the rung comments I can get back up to speed on the particular project (I currently have around 350 old projects to look after too).

This is where rung comments can help you navigate through larger programs very easily I find.

But that's just my opinion, and everyone has one of them!

Answered Sometimes


I dont comment every rung, just each logical portion of code with the appropriate rung comment at the beginning

edit: And the comment explains if needed what each of the 5 (for instance) rungs below do if its not completely self explanatory by the bit comments