Speed Measuring Device For This Kind of Shaft

One solution is to mount the speed probe on a bracket that moves up and down with the shaft, if that is possible.

Another solution is to electrically derive the speed from the motor turning the shaft. For example, if the shaft is turned by an induction motor powered by a VFD, you may approximate shaft speed based on the output frequency of the VFD.

Would it be possible to use a ball spline in a section of the shaft? This will allow the ball cage to rotate in a stationary position with the shaft able to move freely in the vertical direction.

paint a white line all along the kelly shaft and use something like this in a fixed position.

http://www.shopextech.com/p7258/extech_461700.php

That's what I was thinking--a painted line of some contrasting color extending some length along the shaft so that the sensor can remain stationary while the shaft rotates and moves up and down. A magnetic strip would also work--depends on what your sensor can read.

If this is driven by a kelly bushing from a rotary table you can mount the probe (pepperl fuchs induction coil?) underneath the deck in an area where you do not get any vertical movement.

The drive spline on the table motor will have similar "targets" to what you are aiming at on the hook assembly.

It gets pretty dirty & nasty down there with drilling mud and the like so any sort of optical device would have an issue.

The overhead drive does not have,RPM,to the

Golograph? Or is it rotary table driven?

Why cant the counter ride the drive? Then

the up and down would not matter.