Hi Tom I agre the educational aspect of time nuts is great and I have learned a lot but it would be even more useful if discussions include what can be attained and what may be in the reach of time nuts. I used to have a HP 2804A with matched probe prom only used it once when developing a super efficient boat air condition system running on batteries. After that used it to sort of calibrate my YSI probes and sold the unit. I do not think I need any accuracy better than 0.1 C and feel comfortable having it. But if time nuts find a way to get an affordable solution I would get one. We use fan speed temperature control and at one time I did use it on a Tbolt. May revisit it discarded it because of my concern of fan noise transferring to the XTAL in the OCXO. We use it successfully with NTC embedded in the base plate of FRK's and using a separate sensor see 0.01C. Also use heat pipes. In all cases we use voltage control do to my lack of PIC programming experience. In our work the OCXO is not in the Rb but Rb , fan and OCXO all have vibration isolation. The challenge is reliable fan start at low voltage if you want the unit stay constant over an ambient change of 10 C. Members have talked about u processor control but I have not seen any thing that works, many of the heat pipes used in laptop do have digital speed control, some one please step up to the plate. Back to the Tbolt it is tempting but right now I have to many things on my plate. I suggest controlling temperature in an enclosure within 0.1 C along with added mass to the unit, reduce other heat sources in the unit. An other approach would be a heat pipe again more thermal mass and all sides with thermal isolation to reduce ambient temperature. influence. I have an analog fan conrtol board and the plan is to make one available for those that buy a FE 5680A kit. Again maybe some one steps to the plate and designs a digital control. Bert Kehren In a message dated 7/21/2014 3:17:16 A.M. Eastern Daylight Time, [email protected] writes:
> What I am missing in all these discussions is what do we want to archive > or is this an other paper only discussion. I am used to starting out with a > goal, and tackle the challenge from there. > We have a saying in German "Papier ist geduldig. Translate You can write > any thing on paper. > Bert Kehren Hi Bert, Let me answer in two parts. 1) The issue of precision temperature sensing is so key to the field of precise time & frequency that any thread that attracts more information, anecdotes, and wisdom from the group is very welcome. Quartz is such an amazing substance that its use as a precision sensor is every bit as interesting as its use as a precision timekeeper. Not everything has to be goal oriented. Some discussions on this list are pure enjoyment, others highly educational, and some simply plant seeds. Starting with concrete goals is good for a business but when working with precision timing as a hobby, as most of us are, goals are sometimes secondary to just learning or playing around. 2) If you want an example of a specific goal related to temperature, try this: There have been several discussions over the years about variable fan speed based temperature control. I can't explain it, but I've always been suspicious of this technique. It seems to me still air is inherently better than moving air. Passive (no fan) is better than active (fan). And constant velocity is better than turbulence is better than variable velocity. But I don't know for sure. That's where experiments and measurement come in. To satisfy my curiosity and get actual data I'd like to place 6 or more tiny analog high-resolution temperature sensors all around the OCXO of a Trimble Thunderbolt. That's high-resolution both in temperature and in time. In other words, no fake accuracy "averaging" allowed. The goal is to observe thermal gradients in real-time and see how good, or how bad, the correlation is among crystal temperature, case temperature, and DS1620 temperature sensor (which is mounted a considerable distance from the OCXO). The same technique, and maybe even the same conclusions, might apply to Rb. /tvb _______________________________________________ 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.
