Precision wirewound pot wiper bounce?

Can you add a cap to debounce it?

Ed

What's loading the wiper? Just the scope probe?

With just a probe, the fall will be a couple pF || 10M (or 1M), rather = slow. The rise is actually faster than most SS, limited by lower = impedances (charging that couple pF probe with a Thevenin source of = around 2.5kohms).

Back in the day, Tektronix had a pulse generator using mercury-wetted = reed relays. Easily 1ns edges.

It's kind of funny that mechanical devices are so slow and sloppy, yet = generate harmonics out to insane frequencies. The switch doesn't make = full contact for at least a few microseconds, so the edge is caused by = point contact alone. At low voltages, quantum tunneling will carry = current across the gap a few nanometers before it touches. Over 50V, in = gas, arcing will occur at some distance. In high vacuum, this is = replaced by field emission at high electric fields (usually leading to = sputtering and vaporization of the contacts, so there is wear even on a = vacuum relay). Needless to say, any of these contact methods has high = resistance and high current density until things settle down and the = contact area widens (which takes a few bounces!).

Tim

--=20 Deep Friar: a very philosophical monk. Website:

Yes. Guess that's normal for no-load scenarios then. BTW, the bouncing has cleared up nicely after wiping back and forth in the bounce areas as you and others suggested in the components group.

However, as stated eariler, my experience with wirewound pots is that the bouncing will return especially after lack of use. Others have suggested a film of dirt/dust/oxidation/stale lubricant on the element/ wiper may be the culprit.

Another fellow seems to >

Actually, that's the first th>

Some pots that work in the range of 3 turns are built with small planetary mechanism of three ball bearings that roll in a groove in the end of the adjuster shaft. Pressure applied in the mechanism makes the bearings roll nicely on the shaft giving a 3-1 turns ratio of shaft to element. Sometimes one can force a slip between the bearings and the shaft by applying excess force at the end of the normal rotate range.

That is a cheat on the claim then.

It is STILL a single turn pot at that point, regardless of any "hat" mechanism they plant onto the top of it. That is really sad.

Unlike a car's shaft rotation, which is incremental applications of torque, this scenario is advertised as some greater wiper lineal traverse, which would make for a finer resolution incremental 'step' in resistance at the wiper. And it is not that at all. There is no gain over a single turn device at all, in fact. The user can make fine adjustments without backlash better than a planetary gear setup can.

That is also the whole reason that ten turn pots were made to begin with. They make the number of bumps steps greater in number, but smaller in size.

When he said that "ten turns is too fine", but he wants more than one, I thought to myself that he should just go for the ten turn then. Especially if it is simply a set point pot on a circuit. We use the little ten turn guys on all our stuff in that realm, and they are considered "instrumentation class" devices by the industry, and that is their purpose.

Folks simply did not build high class products with el cheapo car stereo class parts from the seventies.

Single turn pots are out. Ten turn pots are cheap. Problem solved.

The pot in question is not a trimmer pot. Long story short....I would not be able to simulate fast acceleration/deceleration, using fingers alone, with a 10-turn pot. This is a somewhat "outside the box" use of a function generator.

OK, then make a chain and sprocket reducer/overdrive.

Then you can make it turn ten times to your three-on-the-fingers or whatever ratio you come up with.

THAT scenario is far better than buying a pot where they took a single turn pot and made it take 3 turns to turn it. Taking three turns to turn a ten turn pot is a far higher resolution adjustment from a 'noise' POV, with 'noise' being transition spikes made between wire contact nodes.

They should sell ten turn pot assemblies where the user can make the ten in less turns based on what gears he puts in the box.

Just like the drill press pulley arrangements.

Naaahh.. too much like mechanics for the engineers to grasp that one.

The pot in question spreads the resistance linearly over 1080 degrees rotation of the knob. I think you misunderstood the poster who mentioned the planetary mechanism used on **some** multiturn pots.

You didn't read enough of the thread.

Your fixati>

You don't seem to understand. It matters not how many turns it takes if the actual wiper is only making a single turn. The lineal distance the wiper takes and length of the resistance medium is what matters.

Making a mechanism to spread a single turn out to three does not give one better, less noisy resolve or stop point achievability.

I understood him perfectly.

One CAN take a ten turn and step DOWN to a lower turns count and keep high resolve and stepping. One cannot get there going the other way. It is 100% counterproductive and gives a false sense of higher precision where none exists.

In that case, when/where did he say that the 3-turn pot in the link below uses the mechanism you just described;

If he didn't then why have you assumed that is the case >

I never said that he said anything. I only referred to what I referred to. It had nothing to do with him other then that he spurred my thoughts on the matter.

Are you all caught up now?

Single turn pots have better symmetry than multi-turn pots, so they might behave better with temperature changes. Back when analog instrumentation was common, I designed instruments with big custom single-turn WW pots and with a gear train which stepped up 270 degrees or whatever it was 6" or so diameter dial (144mm x 144mm DIN standard) to a 3:1 turn helical pot (same construction as the 10 turn pots, but we didn't like the friction from a 10:1 ratio) wot we got from some outfit out in Oceanside CA (I think it was actually a Japanese part). The user interface had to be a single turn dial for the direct reading deviation to work.

Yes....Some>

The two of us? Naaaaaaaah!

The link I gave you is NOT for a trimmer pot. It is for a 3 turn conductive plastic pot like you asked for. So WTF is the problem?

I didn't ask for anything, dingledorf.

Only problem I see is that the thread has gotten a bit long/convoluted and you're confused. I thanked you for that Copal link several hours ago.