On Aug 8, 1:19*am, "N_Cook" wrote:
Winfield Hill wrote in message

...

We have about 10 Agilent 33120A frequency-generator / synthesizers
*in our lab, and a few other similar synthesizers. *They feature a
*convenient digital frequency and amplitude programming knob that's
*based on optical encoders. *A pair of left-right pushbuttons sets
*which decade you're adjusting with the knob, and over or underflows
*operate on the next higher decade. *There's a little indent near
*the edge of the knob so you can spin it with your fingertip. *You
*can also use up-down pushbuttons or directly punch in numbers, but
*the spinning knob is very convenient. *Typically such encoders have
*16 or 32 ticks per revolution. *A very nice design feature.

*The optical shaft encoders were originally made by HP, but now of
*course they're made by Avago. Sometimes they call these a digital
*potentiometer or a "Panel Mount Optical Rotary Encoder". *For
*example, the HRPG-AD16 product line, about $34 each at Mouser.

*http://www.mouser.com/Search/Refine....word=HRPG-AD16

http://www.avagotech.com/pages/en/mo...r_products/rot...
tches/hrpg-ad1616c/





*Since they use an optical 2-bit quadrature grey-code (as opposed
*to using a pair of switch contacts), they're supposed to be
*extremely reliable.

*But recently I've encountered two instruments with identical
*tuning-knob failures, one in an elegant 33250A 80MHz model
*that's on my bench, and the other in one of our standard
*33120A 15MHz instruments.

*In both cases the knob seems 'stuck" and not to work as you
*turn it, except every now and then you'll get one or two
*increments or decrements. *Totally useless.

*I'm wondering if anyone else has encountered this failure?

--
*Thanks,
* * - Win

Its probably patentable so is there a patent outline for them somewhere, to
show what the innards are?

Lots of video editing gear uses optical shaft encoders. Typical
failure is bushing wearout that alters the alignment of the rotary vs
fixed disk. You'll find excess axial 'play' and often side-side play
as well. Some decent lubricant early on sold have increased the life.

G²