Ladder Lines per hour

Hi all,

This is my first time posting a question here, but I have been browsing the forums for a couple of years now, and there are a lot of smart people here, so I'm sure this will be easy for you guys

Here is my question:

In general, how would you evaluate the time it takes to program a PLC from having the control philosophy in hand (no program) until comissionning is completed?

Notes:
My current project is a 60 line (aprox.) program on a S7/1200 for HVAC-R control purposes.

I am aware that every project is different, and that unexpected problems might pop up and add to the total time. I dont expect an exact figure, just a ballpark one.

I will also have to program an HMI for the same project, could you also ballpark a (separate) programming time for this?

Thanks a lot!

I usually estimate my projects starting with the I/O count. I usually give 1 hour per discrete point and 2 hours per analog point. From there, i factor the estimate up or down depending on the complexity of the program. That gives me a fairly good estimate.

I like your method edwardt, but does that include program documentation such as a functional description of the program, or do you assume that the mechanical guys give that to you?

How do you estimate your field time for commissioning?

That was assuming that the functional description is being created by someone else and handed to you.

That really depends on the scope and what field commissioning means for that particular project. For me, sometime it means just dropping in the PLC and HMI programs and stepping through a sign-off sheet of the functional description. Other times it means do that plus setting up instruments, performing loop check-outs, instrumentation calibrations, motor rotation checks, etc. Again though, each of these functions is based on a multiplier times the number of I/O points.

My advice, break your estimate into very small, manageable tasks that you can easily estimate. It is very normal for me to have estimates with every task broken down and some sort of labor unit applied.

Which is easier to estimate? A scope that says "commission the system". Or one that says "Download the program, then loop check every analog I/O, continuity check every discrete I/O, Check rotation on every motor."

Have a scope of work nailed down, and then break it into manageable chunks.

Thanks guys. This all makes sense, especially the "break it down into small chunks" part.

The figure I got now is 8 discrete IOs, 6 Analog IOs and 4 RTD inputs = 90 hours for programming&commissioning, PLC only (not HMI)

Does that make sense to you guys?

What does commissioning mean? What do you have to do for that? If commissioning is really basic and the functional description is basic, i'd say 90 hours is enough, assuming a competent programmer is doing it.

edwardt said:

What does commissioning mean? What do you have to do for that? If commissioning is really basic and the functional description is basic, i'd say 90 hours is enough, assuming a competent programmer is doing it.

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In this case, all the instruments, switches and actuators are already wired, and I don't expect I will have to do any loop checking. I will go through the sequence of normal operation and confirm that the system is working according to the functional description (which is relatively simple). I have set aside 3 days (8h/day) for commissioning.

I would not use ladder lines per hour or even I/O count.
Some the boolean stuff is trivial and takes only a moment to enter it.
Making state machines and using PIDs requires much more effort per line or I/O.
One should also factor in a degree of difficulty depending on the application and its requirements. I would also charge more if who ever picked the PLC did not pick one adequate for the job so it takes a lot of work arounds. For instance there was a recent thread about generating a cosine function in a ML1200. I would charge enough so the next time a PLC would a cosine function with REAL numbers would be specified.

montreal_controlsguy said:

In this case, all the instruments, switches and actuators are already wired, and I don't expect I will have to do any loop checking. I will go through the sequence of normal operation and confirm that the system is working according to the functional description (which is relatively simple). I have set aside 3 days (8h/day) for commissioning.

Click to expand...

I've only been in the automation game for two years but my advice is loop check every point in the system new or old. When you walk away your nae will be on it and you have to prove it works for yourself and them. If an existing point fails a month from now and causes an issue you will be the fall guy. Find that issue now rather than later and sleep well knowing it will do exactly as it should. I always try to recommission off existing I/O or have them sign off that they chose NOT to recommission it to cover my a**.

Kraken Fan #69

krakenfan69 said:

I've only been in the automation game for two years but my advice is loop check every point in the system new or old. When you walk away your nae will be on it and you have to prove it works for yourself and them. If an existing point fails a month from now and causes an issue you will be the fall guy. Find that issue now rather than later and sleep well knowing it will do exactly as it should. I always try to recommission off existing I/O or have them sign off that they chose NOT to recommission it to cover my a**.

Kraken Fan #69

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Good point Kraken...

So how many hours would you add to test all the loops?

I don't really do pricing so I would have no idea. If all the electrical is ready when you get to site and the points are relatively near each other. (so you or your instrumentation tech is not having to walk back and forth across site to set up) You should be able to bang off 8 DI, 6 AI and 4 RTD's in about an hour. Moer if you are having to run both ends of the loop. That's best case so plan on spending more time if there are wiring, device, or other issues. Sometimes during commissioning you will uncover an issue that will cause oeprations to want to rework how the program functions based on how a signal is coming in so having a little buffer there (and charging an extra for the change) willl keep you from losing your shirt. Make sure your contract has whats covered in the bid, spells out extras and how they will charged as well.

Good luck.