Problem with quadrature encoder

[Steve Compton]

I just got his from one of my programmers who is playing with encoders. Can anyone provide some guidance after reading the description below?

Gotta problem... We have used encoders for various things this year.
In each of these cases we have used the encoders to measure position. Just the angle of something.
The encoders also have a "rate" pin on them. It tells us how fast something
is spinning which is what we need for traction control.

We have noted that that the encoder, when measuring "rate", measures
zero after a short time of working correctly. In other words, we spin
the wheel, the rate pin shows a velocity, and then after a short
distance, the rate pin no longer measures velocity (it shows zero).
Then once we stop the wheel, and start spinning it again, the rate will
be measured correctly again for a short distance before falling to zero.

We found a usfirst thread on this that is a month or so old. It says
that an encoder in quadrature (4x) mode (which is what we have), will do
this but if you use the "averaging option" of 1x or 2x it will be fine.
We don't see this. It breaks reliably no mater what averaging we use.
It also says this will be fixed in the next cRIO update. It's not.

Thanks in advance!