Hi The advantage a wire wound pot has is that all the wire is (nearly) the same temperature coefficient. This ~$15 Bourns part:
https://www.digikey.com/product-detail/en/bourns-inc/3590S-2-103L/3590S-2-103L-ND/1088586 <https://www.digikey.com/product-detail/en/bourns-inc/3590S-2-103L/3590S-2-103L-ND/1088586> (Buy 10 at a time and they go down to $13.25 each. ) Has a rated tempco of 50 ppm / C. That’s without taking any matching into account. With the matching you probably are sub 1 ppm/C. The DS1804 has a “typical” temperature coefficient of 750 ppm / C. (from page 5 in the data sheet). Unfortunately there is no reason to believe that all the “bits” have the same tempco. Indeed there are good reasons to believe they vary more than a bit. You would be doing well with a heater that drops that to an effective 75 ppm / C. A 10 turn pot is ground isolated. There are no side effects from power and ground connections. Never underrate the value of isolation. Bob > On Jan 29, 2020, at 8:34 PM, Perry Sandeen via time-nuts > <[email protected]> wrote: > > Learned Gentlemen, > I appreciate all the reply's to my questions. > Perhaps I should have added a bit more detail of my planned project after > moving. I have 5 Lucent XO's and two Lucent Rb's which I want to add panel > mounted fine EFC controls. > I did consider Bourn's Helipots, but found used on ebay were $20 to $30 each > and none had more than two for sale. I did look at the ebay Bourn,s > *tribute* pots with dials from China which seemed to have the exact same item > from $10 to $2 (with free shipping). I remembered that Charles Steinmetz had > posted to the list that he found many of a lot he purchased were defective. > So I went alookin (southern USA term for searching) for a viable alternative, > hence the Maxim DS 1804 non-volatile 10K pot with 100 taps that has a simple > toggle up or down interface. (I have no ability to do serial or computer > control. I found a Microchip AN 691 which showed how to use two or three > digital pot in series/parallel configurations. > Three DS 1804's and a good reference IC for less than $10. A simple TL431 or > LM723 heater circuit would be $2. So with 100 taps on each IC, I figured > (with lots and lots of toggling). I could achieve sub-millivolt or better > tuning steps. > And I was fairly certain that fine EFC tuning was like grandma getting ready > for church on Sunday. She was ready when she was ready. No amount of fussing > or cajoling could change that. It occurred on her time (slow) table. > Comments appreciated. > > Regards, > Perrier > > > > > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
