We’ve got a problem in the field.
We’ve classified the symptoms,
And collected the failed components.
What now?
There are several options we could go with here, but a good middle ground is a technique called Fault Tree Analysis. It can be formally written down, but more often it’s a natural progression of investigation that happens live.
We start with the symptom, and just keep asking Why? or What could cause that? until we find the root cause of the problem.
Let’s say we’re seeing an overspeed condition on a motor driving a pump.
Start with the symptoms - Measured overspeed
What could cause that? Faulty speed sensor -or- Speed command too high -or- something else
What could cause the speed sensor to fail? Bad supply voltage -or- damaged physical component
What could cause the speed command to be high? Incorrect feedback signal (flow measurement) -or- failing motor driver
Keep walking down each branch of the tree until things start making sense!
Once we get there, close the loop by triggering the root cause in a working system, and see if we get the original symptoms. If we do, we’ve got our answer!
-Brian Schoolcraft
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