pot issues!!

-------------------------------------

I have just replaced a pot that was replaced by one of my operators
because I thought that he had connected it up badly but it seems we have
greater issues.

The pot controls the speed at which a cnc mahine runs. It originaly was 0%
- left, 50 - %center and 100% full right. Now at about one twentieth of
the way round it is already at 100%.

Could it be that the cnc tech told me to get a pot with wrong amount of
resistance?

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Could be, but more likely, you replaced a linear pot with an audio
(log taper) version. They have most of the resistance change
concentrated at one end.
http://sound.westhost.com/pots.htm#taper

 

.... maybe you need a "medicinal pot!" <grin>

John

 

Good morning, Kristen. You're right -- it might be possible the tech
told you the wrong part number. As another post mentioned, it could
also be that you've got a log taper. And pots have been known to be
mislabelled - checking with an ohmmeter is a good idea.

A couple of other things:

* If there are three wires going to the pot, it's possible the wiper
wire and one of the leg wires were accidentally exchanged.

* A defect in manufacturing may result in intermittent contact between
the wiper and the resistive element in the pot. It's a good idea just
to take out the pot and check for this. You can also look at the log
taper issue, as well as that it has the right value, and is not
mislabelled.

* Be sure to recheck the relevant connections and solder joints --
you're in an environment with some significant vibration, and something
may have worked its way loose.

Good luck
Chris