encoder values fluctuating considerably

[sdaustin]

Originally Posted by Ether

What Mark said. Plus:

... damage to the disk (e.g. scratches) from improper handling

What Mark & Ether said, plus:

We recently noticed an interesting issue with an E4P encoder codewheel disk. It turns out that the reflective stripes on the codewheel disk from which the encoder picks up the pulses are not applied directly to the disk itself. Rather, they are applied to a plastic film disk that is attached to the codewheel, probably with an adhesive of some kind.

After removing the codewheel from the shaft for cleaning, we found that this plastic film was spinning relative to the disk. There was still a relative tight interference fit of the the plastic film disk to the hub of the codewheel, but it was easy to make it spin on the codewheel and you could easily peel up the edge.

In the past, we have cleaned the codewheel disk with rubbing alcohol & a Q-Tip and alcohol-based eyeglass cleaning wipes, and I suspect the alcohol seeped under the plastic disk and dissolved the adhesive. Probably won't be cleaning them that way in the future. :-)