Scantime Automation & Training

Blank PLC Program

Blank PLC Program

Working with a Blank PLC Program to Locate the Fault

We were recently called onsite to diagnose a production issue as the original supplier of the system was unable to assist, the fault was centred around the speed of equipment where the lateral movement of the hardware was noticeably slower than usual causing several problems with production. The PLC in question was a Mitsubishi Q Series PLC that was interfacing with several Siemens IM151 Slave Units.

Unfortunately, our client had no commented backups of the PLC software which meant we had to use the uploaded copy of the design from the PLC, however a common occurrence with Uploads is that symbols and comments aren't uploaded leaving us with what is essentially a blank program, another issue was when this design was uploaded, it appeared that areas of the code were actually missing.

Luckily for our client we like a challenge and we were able to analyse the Ladder Logic and SFC code and work out where the problem was located.

The fault appeared to be situated on one of the Siemens IM151 Slave Units and after further work we were able to trace the problem back to a broken or damaged wire within an Encoder wiring connector on the production line.

The cabling was replaced and production was able to run at full speed once again.