Jason, Patrick, Peter, Rick

In summary:

1. We could not get the spare interlock chassis to work. The original is back in.
2. We restored the C:/TwinCAT directory to a backup that Peter took in June of 2014.
3. The PSL is running again.

The spare chassis was swapped in. The status screen no longer made sense. Pushing the interlock button made the wrong indicator turn red. I did a scan of the EtherCAT modules. It appeared to indicate that they were unchanged (that is the spare had the same modules in it as the original). Suspected maybe the safety PLC inside the interlock chassis had to be started separately? It seemed to require a username and serial number and password. Peter's attempt to enter these and start it did not appear to work. I tried restarting various things including the entire computer. No luck. I suggested resetting all of the variables including persistent. Bad idea.

Starting the PLC now gave divide by zero errors and would not run. It appeared that some of the persistent variables, which were now all zero, were used in the denominator of fractions. They appeared to be related to some calibration settings. We couldn't get by this. This confuses me. If the code does not start with them zero, and upon the first run they are by default zero... How were they initially set?

It appeared that the files for the saving of the persistent variables were located in the C:/TwinCAT/Boot directory. We tried replacing that directory with a backup that Peter had. This did not help, same divide by zero errors. We tried to delete and replace the entire TwinCAT directory. Windows would not let us delete it.

At some point scanning the EtherCAT modules started showing a whole bunch of differences and the light on the front of the interlock chassis no longer came on.

We decided to put the original interlock chassis back and try restoring the computer to a backup that Peter had taken in June of 2014. After the original chassis was put back the light on the front still did not come on. Peter tried restoring just the TwinCAT directory with the restore software. He was able to do so. We opened the link to the visual. It seemed to run but was blank. I closed it, opened the system manager and set it to run. I opened the PLC and logged in. The light on the front of the interlock chassis came on! The PLC was running again.


Remaining questions:

1. How were the persistent variables originally set? Are what they are set to now (from the backup) the same as they were before?
2. What is different about the spare interlock chassis? Could it be some programming in the safety PLC? Different wiring?