[time-nuts] OXCO Issues -- Latest

[Jim Lux]

On 5/12/13 12:38 PM, Al Wolfe wrote:
> Years ago we were taught that it was poor engineering practice to use
> pots to trim a DC value, especially if any appreciable current was to be
> drawn from the wiper. (Probably true for any kind of signal on a pot) It
> seems that current through the wiper would eventually erode away the
> material under the wiper. This is true especially for set-and-forget
> applications. If the wiper is used only as a voltage reference and very
> little current drawn then it is probably OK for most situations.
>
<snip>

> Probably the best design is to use fixed resistors for most of the
> voltage divider circuit and the variable element be a small fraction of
> the total divider resistance.
>
> Al
>
>

This is what those EEPROM based electronic trimpots are great for. 
(assuming you fit within the other limitations of use). Basically, 
they're an array of FETs on a resistor network, and even with the power 
off, they have the same value.