Hi Nigel, I didn't give any thought to thermal issues when I bought the resistors. They're just standard carbon composition. I see some metal film resistors with a temp coefficient of 5 PPM/C, so I'll get some of those and put them in.
thanks, Bob >________________________________ > From: "[email protected]" <[email protected]> >To: [email protected] >Sent: Friday, January 31, 2014 11:35 AM >Subject: Re: [time-nuts] EFC divider resistors > > >The problem is certainly real enough. > >What you're seeing is a drift of approx 2500ppm, and Vishay shows the >temperature coefficient of their standard carbon film resistor, for example, >to >be approx 200ppm per degree C for a value of 20K. > >If yours is carbon film this would imply your measured resistor is seeing >a temperature rise of around 10 or 12 degrees C, which might be a bit on >the high side but is certainly feasible given a body temperature of around 35 >degrees C. > >Standard metal film resistors have a lower temperature coefficient, say >around 50ppm per degree C, so this might be one option for reducing the >effect, another could be temperature control of your EFC network. > >There are more specialised resistors with much lower temeparature >coefficients, the Vishay RCME series of metal film resistors for example can >be as >low as 5 to 6 ppm per degree C, although I don't know what the cost >difference might be. > >And no, I don't have any shares in Vishay:-) > >Regards > >Nigel >GM8PZR > > >In a message dated 31/01/2014 17:04:24 GMT Standard Time, [email protected] >writes: > >I put a divider network in the EFC line of my GPSDO to restrict the OCXO >range to 2Hz. Now I'm seeing heat-related drift that wasn't apparent >before. I put a 20K resistor from the same strip on my 3456A, and the warmth >of >holding it between fingers moves it by about 50 ohms. What type of >resistors should I put in there? Or am I chasing a problem that doesn't >exist? >Totally out of my league here. > >Bob - AE6RV >_______________________________________________ >time-nuts mailing list -- [email protected] >To unsubscribe, go to >https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >and follow the instructions there. >_______________________________________________ >time-nuts mailing list -- [email protected] >To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >and follow the instructions there. > > > _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
