Jerry No one has seriously suggested that the temperature sensor is used to control the oven temperature. It is likely to merely an input to the Kalman filter to allow for compensation of the EFC DAC gain and offset drift as well as the effects of finite OCXO oven thermal gain. Thermal hysteresis will limit the stability of the external EFC DAC after such correction.
The question is really is what effect (if any) does the apparent 0.5C quantisation error have on the performance compared to the earlier versions that have greater resolution? If the external DAC has a gain and offset tempco of 10ppm/C and the OCXO EFC range is 1ppm, then 0.5C temperature resolution can potentially cause 5E-12 steps in the fractional OCXO frequency after correction for DAC gain drift. If the DAC experiences wide temperature swings then thermal hysteresis may cause variations of several ppm in the DAC gain and/or offset, in which case there may be little point in using a sensor with a resolution of better than 0.5C. The sensor itself may have significant thermal hysteresis. Bruce gsteinb...@aol.com wrote: > Why the doubt? > Couldn't this just be one input to the Kalman filter? Does the external > electronics package require the same temperature regulation as the OCXO? > Why not put a cold pack on the DS chip and see if the OXCO output swings as > wildly as you expect (I think it would be irresponsibly poor design to > control > the OXCO outside of the crystal component). > Perhaps the early units had microdegree resolution for ambient air, but that > doesn't mean the application *requires* microdegree resolution. > > Jerry > > > > > > Message: 6 > Date: Thu, 5 Feb 2009 18:44:08 +0000 > From: Mark Sims <hol...@hotmail.com> > Subject: [time-nuts] Tbolt temperature sensor > To: <time-nuts@febo.com> > Message-ID: <blu125-w41a5b9f9f57936e392bf0ece...@phx.gbl> > Content-Type: text/plain; charset="Windows-1252" > > > I doubt the temperature sensor is just used for environmental monitoring. If > it > was, they would most likely have just used the basic 0.5C resolution reading > and have been done with it. Instead, they do the high res read routine > and > then feed that into a filter to get very smooth high resolution (microdegree > scale) values. > > The whole purpose of a GPSDO with an expensive double oven OCXO is to provide > extremely high quality holdover performance when GPS signals go away. To > achieve this level of performance one needs to compensate for the affects of > temperature on the parts of the system outside the oven. 0.5C resolution is > not > up to the task of maintaining parts per trillion accuracy. There does not > appear to be any other temperature sensor in the Tbolt. > > > > ------------ > Isn't it likely that a temperature sensor adjacent to the RS232 connector is > just going to monitor unit temperature for environmental purposes, perhaps, > for example, to give the option for flagging up an overheating situation, in > which case surely 0.5C resolution is more than adequate and the "clunkiness" > isn't really an issue? > > _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
