On 25/01/2009, at 6:05 AM, Robert Atkinson wrote: > Hi John, to measure a solid surface I would use a very thin copper/constantin thermo-couple and put the "cold " junction on your thermometer probe in an insulated shield. The "hot" junction goes on the part of the board to be measured. A microvolt DVM is needed to measure the thermocouple, a 1 microvolt difference is about .025 Kelvins. Here you get the lack of self heating of the thermocouple and very small down-lead conduction because of the thin wire, but you get the stability and accuracy of the quartz thermometer underpinning your measurement. There is a neat little quadratic that converts microvolts from the thermocouple to temperature difference. The main difficulty with using thermocouples is the accuracy of the cold junction and your quartz thermometer solves that problem. If you have doubts about your microvoltmeter you reverse the thermocouple connections to get twice the error difference. If you want more bang for your buck wire 5 thermocouples in series, insulate the junctions from each other, and use the composite junction on your board to get a resolution of 0.005 Kelvins,. The reversed polarity trick also works here to remove DVM offset. I know this is not using the quartz thermometer directly but it would be a very good way to measure a board to 1millikelvin. For theoretical reasons a thermocouple can not have a temperature offset. cheers, Neville Michie
> --- On Sat, 24/1/09, John Ackermann N8UR <[email protected]> wrote: > >> From: John Ackermann N8UR <[email protected]> >> Subject: [time-nuts] Any experienced HP 2804A thermometer users >> out there? >> To: "Discussion of precise time and frequency measurement" <time- >> [email protected]> >> Date: Saturday, 24 January, 2009, 3:42 PM >> The temperature probes for the 2804A quartz thermometer seem >> primarily >> intended for liquid immersion. I'm looking for >> practical tips on how to >> couple the probe to a solid surface (e.g., a PC board) for >> accurate >> temperature measurements of the surface. >> >> Anyone know the best way to do this? >> >> Thanks, >> >> John >> >> _______________________________________________ >> 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.
