Multi-turn Trimmer Pots - Locking the Adjustment?

[large_ghostman]

Matt your 371 is fine , its not all plastics and you need a fair bit. plus as it hardens it forms a coat, the helicopter thing comes from them building the the things out of it, not using a couple of dabs .

 

[large_ghostman]

425 you wont move......EVER

Edit thats the wrong one, i was thinking of the spline gear one, the number escapes me, its extremely expensive!

 

[jbeng]

In the past, we used to use "Torque Seal" for locking pots.
But, the rights to that product were sold to Dykem a while back and their product is called "Cross Check".
.

 

[MikeMl]

In the past, we used to use "Torque Seal" for locking pots.
But, the rights to that product were sold to Dykem a while back and their product is called "Cross Check".

Same stuff as used on critical bolts in aircraft structures. It is not to "lock" something, however. It is used to see if the bolt/nut has turned since it was torqued, or if it has moved (or been moved) since the last inspection.

 

[jbeng]

It is not to "lock" something, however. It is used to see if the bolt/nut has turned since it was torqued, or if it has moved (or been moved) since the last inspection.

I get that. You can use it in the same tamper-evident context with a pot... and for something with a small mass like a control screw on a pot, it does act as a locking agent. Both of those reasons are why we used it.

 

[JonSea]

Thanks for the suggestions everyone. We got a little sidetracked on materials rather then if it's necessary.

Part of me wants to do away with the hassle. Part of me feels uncomfortable knowing the pot could turn. It's probably not necessary due to the locking nature of a worm and wheel, as well as the fact that the pot can turn quite a way before "5 volts" would be significantly off.

 

[KeepItSimpleStupid]

Was it moved is useful info. You might be better off to have a fixed resistor matrix of splt pad where selection gets you within the tolerance you need.

 

[gophert]

I get that. You can use it in the same tamper-evident context with a pot... and for something with a small mass like a control screw on a pot, it does act as a locking agent. Both of those reasons are why we used it.

Not exactly on all plastics. A dab on the brass screw and the blue body of the trimmer will get you a dab of your marking dot that bonds well to the brass but may easily slide off of the slick (difficult-to-bond-to HDPE or PP) as thetrimmer s turned ad the strength of the marking pigment film strength making it look untampered.

 

[dknguyen]

you could throw the pot between 2 fixed resistors to effectively narrow the adjustment range and increase adjustment resolution of the pot so even more movement would be required to achieve a noticeable change.

 

[JonSea]

you could throw the pot between 2 fixed resistors to effectively narrow the adjustment range and increase adjustment resolution of the pot so even more movement would be required to achieve a noticeable change.

If I wanted to modify the DC-DC converter modules (exactly the one pictured above), I'd just take out the pot and replace it with 2 fixed resistors. I want 5 volts output that will never need to change.

 

[GromTag]

Multi turn trimmers have some issues with the design in itself.

Vibrations can cause adjustments tho not unless the method is precise as in vertical frequency and circular horizontal axis.

Altho the internal components would resonate, (don't know the frequencies) and bend slightly (similar to an elastic string under tension being plucked resulting in the adjustment parts locking them selves up against any surrounding walls or other conponents internally. Similar to crystal resonance but without Quartz property involved.

The internal ring assembly that contains a clutch disk that resides against some type of interlocking assembly turned by the adjustment screw would have more self adjusting effort via tolerance of the parts with space between the clutch and the ring component and worm gear that could self adjust to about 10 to 30 Ohm in some cases for for 100K Ohm trimmers that I have used that were in the not so well designd range. So locking the andjustment screw would not compensate for the internal components at all. Just a tale tale of tampering notice only if unique color of locking method is used as to not be duplicatable.

Then theres thermal change in resistance adds to more a slight bit to the self alteration of the trimmer.

The worst case in self adjustment to a correct range trimmer would be similar to trying to use an incorrect range trimmer at say 1 Megaohm trimmer to gain a 10 - 20 Ohm adjustment. That would be extremly difficult to obtain with a 1 Megaohm to say in the least only to have temperature throw that effort it way off any how.

Saying that each trimmer range in resistance value along with manufacturing quality would have some self adjustment by either vibration causing resting of the inner ring untill it props against the clutch in either direction internaly or some thermal drift to contend with.

.... I think all that means tolerance of part by various means.. I could have just said that counldn't I?

 

[ccurtis]

Isn't loctite anaerobic, meaning that it will not harden in air? I've had some of the stuff uncapped for weeks and it never even got thick.

 

[dknguyen]

Isn't loctite anaerobic, meaning that it will not harden in air? I've had some of the stuff uncapped for weeks and it never even got thick.

According to the datashsheet, yes.