IAS Blog

It Sounded Like a Crash

Posted on 04/08/2009 at 03:10 pm by IAS
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Jim and I had been tasked with removing an ILC200 controller and replacing it with a newer ILC150 Controller. The software to program these controllers is called PC-Worx. PC-Worx is an IEC 61131-3 compliant software package. There were a few issues due to differences between the controllers. One issue was that somehow we had lost our default values. There were not that many default values so we manually typed them into the new program.

This machine is enclosed so you can't really see what is going on. It also has about 500lbs of weight that moves pretty quickly during its cycle. Trying this machine with a new controller and converted program can put you a bit on edge.

Jim asked the machine to perform a task. All seemed well until there was a loud crashing sound and a small seismic event. This sent Jim scrambling for the e-stop but as he was about to stop the machine he noticed it had completed its cycle and was waiting for its next task.

This left us wondering, what in the world was that? We removed the covers and inspected the machine. All looked well. No visible damage and the machine had indeed finished its task. We were now well inside the land of confusion.

If you have written and debugged many programs you know that there is a tendency to want to try things again. It could have been a one time event, the problem may not relate to the programming at all. I suggested we try that again to see if it was repeatable. Jim decided this was a good time to tell me a joke.

Three people were in a car that lost its brakes and crashed coming down a hill. A manager, a mechanical engineer, and a software engineer. The manager wanted to form a committee to decide what to do next. The mechanical engineer wanted to use his Swiss army knife to fix the problem. The software engineer wanted to push the car back up the hill to see if it happened again.

I think this was Jim's way of saying, "How about we fix it first". So Jim reviewed the program and found we were missing the deceleration rate for a VFD. This was one of the initial values we lost. The crash sound was going from full speed to a stop in as close to 0 seconds as possible. Jim and I were both very impressed that the Emerson VFD sounded like it came close to a 0 second deceleration.