How to determine if PC file matches PLC program (SLC5/05)

Hello, I have inherited the job of maintaining about 10 SLC5/05 PLCs in a wastewater treatment plant, and along with them a laptop which is "supposed to" have the most recent versions of the programs.

We already learned that one program on the laptop is outdated, because one PLC lost its program and had to be re-downloaded. However, the code on the laptop did not include some modifications that had been made later, so we had to contact the last guy and get an updated version.

However, I am not sure about the other files on the laptop.
Before I start making any changes to the running code, or doing any type of maintenance on the units, I want to make sure I have an exact backup of the actual code running on the PLCs.

When I open RSLogix 500 and Go Online with one of these PLCs, I am prompted to select a file to use. When I select a file, it proceeds to go online and shows the running program.

However, I'm confused: does this mean the program on the laptop exactly matches the program on the PLC? or is RSLogix just using the symbol names and comments from the PC program and showing the logic from the PLC memory?

What would happen if the program in PLC memory differs from the one on the laptop, and how would I reconcile the two?

Sorry if this is a stupid question, and I appreciate any suggestions!

It's a really good question, and it's a very important aspect of the controllers and software to understand.

When you have a *.RSS program open in RSLogix 500 and select "Go Online", the software compares the checksum of the user logic in the online controller with the checksum of the user logic in the offline program.

If they match, then the currently-open program matches the controller that RSLogix 500 has an RSLinx comms path pointed to, and the software goes online.

If they don't match, then the currently-open program does not match the controller that it's pointed to. That's when the "select a matching *.RSS file" window opens up, prompting you to find a program whose Controller Name matches the SLC-500 that the software is pointing at.

If the checksum of the *.RSS file you select doesn't match the online controller either, the software requires that you either upload (PLC -> Computer) or download (Computer -> PLC) the user program.

Going around and uploading and saving current copies of all your installed controllers should be Job One for anyone taking over a plant or department or machine or workcell. Good work !

Thank you very much for your quick reply! I think I understand now.

So as sort of a follow-up question: if I make modifications to a program while offline, then save the program and later go online, I will be given the option to download the modified program at that point?

Again thanks for your help! I'm very quickly learning what a valuable resource this forum is! I'm just sorry I don't have much to contribute back to the forum yet!


Best,
Ryan

If you modify the program while offline then download you will be overwriting the data tables with the last saved values. if these are critical it is best to connect and upload the current program with its data table values then go offline to make the changes. That way there will be the least number of differences.

It is up to you to consider the consequence of downloading changed data to a system.

ryangriggs said:

.......So as sort of a follow-up question: if I make modifications to a program while offline, then save the program and later go online, I will be given the option to download the modified program at that point?

Click to expand...

If you "Go Online" you will be prompted with the Matching File pop up window because the file on your hard drive no longer matches the file in the controller. At that point you will have the option to upload or download.

When you know that you need to download to the controller you could select Download instead of Go Online.

OG

Another option... if you want to see more detail, open RSlogix 500 and click on Tools, then click Compare, you can upload and compare the two projects and see the changes that are in both side by side... just food for thought

I always upload the current plc program to the laptop under a specific directory including the data tables.

I then compare the program to what was on the laptop along with the data file.

REMEMBER, the program in the plc is the working copy! the program in the pc is there for a reference.

if you have to make changes, take the program you just uploaded and copy it somewhere so that you have the master copy as a backup in case a change is made that creates an uh-oh situation.

ALSO, take the pc programs and make a copy and put it on the network with restricted access so that only programmers read / write the file.
others can have read only access. this is your safety in case the laptop hard drive crashes.

regards,
james

+1 on going online and uploading and saving the current data files.

Temperature settings, operating modes, location=encoder value, etc could have changed or calibrated after the upload that was saved - maybe months or years ago, or the file is the original shipped by the OEM and doesn't have all the parameters that have been setup.