Ron_S

Sometimes - the importance of backing up device data

4 posts in this topic

An unusual tale, but in these times of isolation and no work, I'll tell it.

A few years back I went to a machine with an FX2n 64 MR controlling  (for want of a better description) a sewing machine.

I uploaded the program and saved it before I started on the fault finding.

The nice programmer (or so I thought) had saved the comments in the plc too, so it made my job a lot easier.

I found the fault - a proxy that lit but gave no output so it turned out a nice easy job with lots of kudos from the customer.

I stayed a while and watched this great sewing machine. It had 4 sewing heads that moved in and out of each others space with great timing.

 

A few years pass with me never going again and they phone me.

The transformer has overheated and killed the plc. They have replaced the transformer but the plc was dead.

They have also bought a second hand FX2n 64 MR from ebay and swapped that out

They thought it was a part you just replaced and everything would be fine.

 

I explained that the program has to go back in and I might possibly still have it on an old laptop.

I searched my files and I did have it, so I set off to another simple job.......not.

 

I put the basic program back in and it wouldn't work and was doing unusual things.

The sewing heads were jumping and solenoids were firing on and off and all manner of things.

Looking at the program, there were about 200 data registers (timers, counters, maths etc)

But, and I mean but - there was no reference to these data registers apart from where they were in the logic

By this I mean, there were no lines like MOV K3 D100.

I wrote some dummy logic using MOV's and could see they were all at zero.....

The programmer must have punched the values in one by one using 'set device'

I could see no reason for this until I realised that because he had used a lot of memory on the comments file, there was hardly any memory left for the program (strange eh)

He didn't have the space to put all the MOV instructions or he would lose the comments 

 

Luckily, my routine when first uploading a program is to save it with everything including data values and then re-upload a new copy of the program to work on.

I had the data files saved and put them in and all was well.

 

What a funny way to program.

 

 

 

 

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A lot of people program that way.  I think the intent is to go back to put some "default" values in but they often don't go back to finish that step.  

On another note- I used to work for a distributor of Mitsubishi.  I would commonly run into the problem where someone had uploaded their programs using Medoc to create their backups.  For small, simple machines this would work fine.  For PLCs that were programmed using the GPP units, we would often run into a problem where whole sections of machinery would not work.  The problem was that the GPPs had tables that could be filled out to configure their remote I/O networks.  Medoc did not have these tables, so when the program was uploaded, that data would not get uploaded.  Therefore, when the program was downloaded again, the remote I/O would not work.  For users of Medoc, the TO/FROM instructions needed to be added to the program in order to configure the network.  In this case, people thought they were doing the right thing and because of a large gap in functionality between Medoc and the GPPs, they would get hosed.

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4 hours ago, Ron_S said:

Luckily, my routine when first uploading a program is to save it with everything including data values and then re-upload a new copy of the program to work on.

This is my routine as well due to a similar experience with an old Omron PLC. Your customer probably doesn't realize how lucky they were.

3 hours ago, drforsythe said:

GPP

Wow, he said, "GPP". A member that doesn't mind showing his age!

I didn't realize the GPPs had that function over Medoc. It's interesting what we learn many years later.

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hmm...on a similar angle, if the PLC battery and Memory battery are good and you pull out a CPU and then reinstall it, all should be maintained yes? I see that comments gobble up space and in this instance, there are not any comments in the PLC ( I was starting to put them in and seen the impact on memory right away)

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