EMRFD Message Archive 14525

Message Date From Subject
14525 2018-01-30 22:08:08 w0ep component question - vernier drive
this may not be exactly the right forum, so I apologize
if that's the case.

I'm taking apart some old laboratory equipment and this thing
has some vernier drives set up on potentiometers in a way I had not
seen before.

There is a normal 20k potentiometer. ("20kLN"  linear?)
There is a knob which turns approximately 270+ degrees.

But between the two there is a reduction drive with stops, so that the
range of the potentiometer movement is greatly reduced.  The ~270 degree
turn of the knob maybe turns the pot by 10 degrees, and that's it.

What electronics or user interface purpose would make this design

Chris Howard
14526 2018-01-31 07:51:43 Bill Carver Re: component question - vernier drive
I used to have a drive like that: when the vernier action stops at the 270 degree ends, it became 1:1, non-vernier. So it was a 1:1/6:1 on one shaft. There was a friction collar between the panel and the outside 1:1 part. If that friction part got corroded to lubrication dried up then it would inhibit the 1:1 function and you'd be left with a 6:1 at whatever pot position the outside froze.

If it is that kind of a drive, perhaps some penetrant would loosen it up again. Then they would be a nice option to have in some homebrew application


14527 2018-02-01 08:41:57 w0ep Re: component question - vernier drive

I put a few drops of tri-flow on it at various points
and now it has two speeds.  The "coarse" is approx 10 turns to
cover the whole range of the pot (20k) and the "fine" covers 700 ohms.

When I first started the "coarse" was stuck.

Now it makes sense!