The immersion depth does make a difference in ultimate accuracy, but 20cm is not required. Per the manual, for the probe I have available, the "immersion error" is 0.001 degree C at 9cm, and 0.01C for 3.5cm insertion. Of course, both are impractical for a surface measurement.
This is clearly a case of picking the right tool for the job! John ---- Henk Termeer said the following on 01/24/2009 11:58 AM: > Hello John, > > I have been searching for pictures and found this > http://www.harlanlabs.com/2804a.jpg if you have a probe like this, no grease > will help you. > The quartz cristal is some where in the bulp on the end of the probe and is > not in direct contact, just like a cristal for a osicillator (because it has > to be able to move), so the thermal resistance between the bulp and the > cristal is high. If you make contact to a pc board, you will measure > something between the enviroment temperature and the board temperature, but > you will never know what you measure most. > This probe is excelent for calibration in liquits or gas but you have to > insert it at least 20 cm. > > Best regards, > > Henk > > On Sat, Jan 24, 2009 at 5:39 PM, John Ackermann N8UR <[email protected]> wrote: > >> The best I can get. This is time-nuts, after all. :-) >> >> I'm certainly not looking for the full millidegree accuracy of the >> thermometer, but have always been curious about heat transfer issues >> with thermometer probes and wondered if there were any tricks apart from >> laying the end of the probe horizontally on the board (maybe with the >> help of some thermal grease, as Brooke suggested). The challenge is the >> relatively small contact area between the circular probe and the flat >> board, and the corresponding fact that the majority of the probe's >> surface area is in contact with the ambient air rather than the surface >> of interest. >> >> John >> ---- >> >> Mike Feher said the following on 01/24/2009 11:15 AM: >>> What type of accuracy are you looking for John? >>> >>> >>> >>> Mike B. Feher, N4FS >>> 89 Arnold Blvd. >>> Howell, NJ, 07731 >>> 732-886-5960 >>> >>> >>> -----Original Message----- >>> From: [email protected] [mailto:[email protected]] On >>> Behalf Of John Ackermann N8UR >>> Sent: Saturday, January 24, 2009 10:42 AM >>> To: Discussion of precise time and frequency measurement >>> Subject: [time-nuts] Any experienced HP 2804A thermometer users out >> there? >>> 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. >> > > > _______________________________________________ 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.
