Re: [CAD_CAM_EDM_DRO] Determining Glass Scale Resolution

Michael James wrote:

>
>Hello group... I need to replace a broken Glass Scale/Encoder but I
>don't have a useful part number. It still works but an end got
>crushed. How can I figure out what resolution it is? I've got an
>oscilloscope, is there any other test equipment I'd need?
>

OK, since it is still working, hook the scope to one of the quadrature
outputs (A,B) of the scale, and make a short move. Count the number
of pulses generated. You will see a burst of pulses with the pulses in
the center of the burst coming the fastest, due to
acceleration/deceleration.
The resolution of the scale will be equal to the number of pulses divided
by the length of the move. For instance, if you see 25 pulses for a move
of .1", that would mean a resolution of 250 cycles/inch. In quadrature,
that would give 1000 counts/inch, but linear scales are usually sold
measured by cycles/linear unit. If this is a very old unit with inch-based
scales, you are in "deep Doo-Doo", as no manufacturer has made
native inch scales in the last 25 years.

It is also possible that the scales are analog, and you will see sine waves,
not square pulses. These are still available, but an interpolator device
refines the measurment to a finer degree. Some of these scales produce
voltages, some produce a varying current. It will be a bit more difficult
to mix and match analog scales, but it can still be done.

Jon