trimpot reliability

Johann

Joined Nov 27, 2006
190
Many times past, I have cobbled up a trimpot, with a specific resistor in parallel, so to dial in a particular resistance value not available in standard... Once I tune that circuit in, I coat the slider / resistance band in a drop of epoxy so no further adjustment is possible...
This is similar to (if not the same as) "panning" a pot. Am I correct? I remember doing this sometimes if the correct pot was not available.
 

ErnieM

Joined Apr 24, 2011
8,377
I have the joy of setting a pot when I'm backing up production testing on a supply we build. While it is a 10 turn pot it suspiciously has a dead zone right around the place I want to set it on every unit. The damn thing loves to jump around values too, and don't even thing of going back "just a little bit" because the backlash is horrible.

It is stable at least thru vibration (6G one axix) and thermal cycling (-40/+60 4 cycles over 8 hours).

Should you want a particular value not in the standard list there is always the possibility of putting another fixed resistor in parallel. That's how we adjusted "military things" where we were not allowed trim pots.
 
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