John, The best way to couple a probe to a solid surface is to drill a hole in the solid that is deeper than the probe. Put some thermal compound in the hole that will exclude air and insert the probe. You must eliminate air between the probe and the surface. Sadly, that won't work with the usual thicknesses of circuit board and the size of the 2804 probe.
This is a simple exercise in heat flow. There are published figures for thermal conductivities of circuit boards, metals and air. There are formulas remarkably like Ohms law relating series temperature drops, thermal conductivity, contact area, and the temperature difference between the source of heat for the system and the sink (which would be the probe leads and ambient air). The thermal conductivity of an insulator like a PC board lies somewhere between air and metal. When you measure a small area of a PC board, that area must cool off unless it is the ultimate source of heat. The only way to avoid that is to have probe leads that are at the temperature you are trying to measure, sort of like a Guard shield for a microvolt measurement. When I think of time-nuts and temperature, oven temperature comes to mind. With a PC board, I'm OK as long as it doesn't char. Can you be more specific about the application? Yours for less speculation and more useful answers, Bill Hawkins -----Original Message----- From: John Ackermann N8UR Sent: Saturday, January 24, 2009 9:42 AM 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.
