Need Some AB help

Hi all,
I am looking for some answers to a project I am currently undertaking.
I am a maintenance Tech. and have learnt by doing with AB so am not aware of a lot of the detail when it comes to dealing with the more complex areas.

I have replaced an Omron C60K PLC with 32 point Flex I/O running on deviceNet from an SLC 504 which is installed on the parent Machine.

I have successfully done this on other machine, however the parent program was much smaller and has a scan time around 15msecs.

On this machine the Program is much larger and the scan time is around 48msecs.

The problem I am facing is. It appears that the I/O is not updating fast enough therfore certain processes are "over running" ie. an indexing conveyor and various other components.
I was able to rectify a few of these by increasing cam angles however I am stuck with the conveyor over running.

my questions are:

1.Is 48 msec scan time excessive and could it be causing this and thereby give me problems with the parent equipment?

2. How much time does deviceNet add to I/O updating? could this be cauing my problem.

3. When running DeviceNet how much care should be taken on the routing of the cable and also the selection of the cable used.

Hope you Guys/Gals can shed some light on this.

regards

Gunner

Well, if the only difference between installations is the size of the program it makes sense to start there. Can you post the program here to allow someone to peruse it?

Scan times can increase not only due to the program length, the more hardware you have can also be the cause. Due you have any stepper drives [1747-HSTP1] on the rack. Once I had 25 of them in a total of 3 racks and the scan times was around 40 mSec.

Or, due you have some for-next loops inside the program, which is causing the increase.... Check for your JMP and Lbl and ensure the scan is not trapped in there unnecessarily.

Good luck.

I am unable to post the programs as I am at home at the moment.

Now that you mention it, there are quite a few hardware diffences as well, additional flex I/O a panelveiw 300, 2 high speed counter cards and a couple of analogue I/O units

It is probably something simple that is staring me in the face.

Thanks Guys I will let yoy know what the outcome is.

regards

Gunner

you can also speed the scan time by making sure the input of every rung is the one most likely to be false (off)

SLC's dont scan the rest of the rung if the first command is false. Cuts down on apparent program length by lots.

The only circumstance Ive had of the above, we put a CLX5555 in its place.


Andrew B

also dont put compare instructions as the first command of a rung

Thanks for all the tips.

After a torrid day being dragged from pillar to post on other Jobs (typical monday startup).
I was able to get into the Devicenet side of things and and speed up the baud rate and alter the node settings from polled to cyclic which has appeared to fix the problem.
Devicenet is a dog to work with, I have never had so many problems with drivers etc.
Just trying to change baud rates on several nodes was a major task in itself. I must be doing something wrong!

Is there somewhere that I can hone my skills on DeviceNet other than hands on and reading the help files? After all it is not something that a maintenance guy has to use very often.

thanks again

regards

Gunner