Messaging?

I am having an issue that I am out of ideas for troubleshooting. I am using a ML 1400 to control a piece of equipment and a Compact logix (1769-L24ER) to deliver 4 different types of chemicals to it, it will eventually be delivering to several machines. I have the first one working very well(most of the time) it may run the recipe 10 times perfectly then either not advance to the next step or advance several steps very quickly. stop the machine, start it again and it may work perfectly 10-12 more recipies. All of the read/write instructions are in the compact logix. I am using a N-tron 900B Ethernet switch. any ideas would be appreciated.

I'll take a stab - may be other reasons but first thing that comes to mind...

Have you made sure each MSG block is complete (check DN/ER) before calling the next MSG block? Are the MSG blocks essentially in a serial, continuous loop or are they instead in parallel? Have you done that for each and every MSG block, including the first and last one? Some of the AB examples are not entirely correct so its easy to mess this up.

By my experience, the behavior you describe is caused when I inadvertently code a MSG block to run in parallel instead of force all of them to run one after the other in succession. If you run them in parallel, the MSG queues fill up and then no more messages make it through.

Thank you, I believe they are all cascading, should not be parrelel but I will check again

Hi and Welcome to the Forum!

MightyJoeOld said:

...All of the read/write instructions are in the compact logix...

...I believe they are all cascading, should not be parrelel but I will check again

Click to expand...

You need to be a little bit more specific. How many is "all"?

One thing to look at is the CompactLogix' processor system overhead time slice. Messages are executed during this phase of the controller's house keeping. Depending on the level of messaging, and the size in elements, this time slice may not be long enough at times to execute all messages fully.

Also, the CompactLogix uses Unconnected Buffers for messages to SLC/MicroLogix. The default is 10 Outgoing Buffers, but this can be increased, with caution, to up to 40 Unconnected Buffers. Again, depending on the level of messaging, the Buffers may be overrun at certain times.

Also, are you are potentially writing data to the ML1400, while it is potentially using the existing data, for what we do not know yet exactly, but it is possible that overwriting the existing, and potentially in use data, could throw a spanner in the works?

While it might be more convenient to do all the messaging in the CompactLogix, it is not generally good practice to write to controllers, or more, to write directly to the addresses in use.

A better practice, if you must write, is to write the data to holding registers in the ML1400, and access the fresh data as and when needed. i.e. the addresses being used in your logic, that are sourced from the CompactLogix, should be indirectly sourced. So at the end of a batch, or cycle, etc., you then update the data locally for the next batch/cycle, and not during.

Do any messages fault?

nwboson said:

...Have you made sure each MSG block is complete (check DN/ER) before calling the next MSG block?...

Click to expand...

I don't believe you have answered this important question?

Regards,
George

Would it not be more practical and logical for the MLs to READ the data from the CompactLogix as and when it needs it ?

For example, it might only need to refresh its working data once per manufacturing "cycle".... You could use the MSG.DN bit as a prerequisite to the cycle start, which would ensure it is using valid data.

Continuously writing the data seems overkill, especially if the ML is executing code using that data. A single MSG READ is all that is needed, which will alleviate MSG buffer and physical network issues

daba said:

...Continuously writing the data seems overkill...

Click to expand...

daba,

I agree. It would be clean and clearer to read the data as and when required. It would also cut down on the total amount of data being transmitted at any given time.

What would concern me more here is what happens when this is the case...

MightyJoeOld said:

... I am using a ML 1400 to control a piece of equipment and a Compact logix (1769-L24ER) to deliver 4 different types of chemicals to it, it will eventually be delivering to several machines...

Click to expand...

If all of the required messaging for that setup is done in the CompactLogix, then what's happening now may seem tame in comparison?

But one other thing we haven't considered yet is this. Maybe the messaging has nothing to do with the cycle tripping up? Maybe there is just something in the ML1400's program going awry?

G.