); SAEximRunCond expanded to false Errors-To: [EMAIL PROTECTED] RETRY This is interesting.
I would like to setup a data logger on a 10811 (with EFC grounded) and record the oven current as well as the output from a 5370 comparing the 10811 to my Thunderbolt and the temperature in my shack. Temperature regulation in the shack is very poor, as it is at the end of the house and upstairs. Large temperature swings are routine, so we should be able to estimate the potential effect of a common ground in the EFC return as temperature changes and see how significant it is compared to the natural OCXO temperature sensitivity. Only problem, the Thunderbolt is in the same room at the moment, and I am not sure how it's OCXO's temperature stability compares to the 10811. I probably need to put the Thunderbolt into an isolated box. Currently, I have a 10811 that has been running for about 6 months from a fairly well regulated 18V supply, so all I need is to put a current sense resistor and send that to one of the microprocessor board I have which is already configured to measure temperatures through standard 10k NTC thermistors (I have 4 inputs available, so I could record the ambient temperature around the 10811 and also around the Thunderbolt). My Visual Basic GPIB data logger can take inputs from the microprocessor simultaneously through a serial port, so I could record current, temperature and 5370 data every second or so. I see another project coming for this week-end... Didier ---- Tom Van Baak <[EMAIL PROTECTED]> wrote: > > I believe the problem is that the EFC closed loop has a significant time > > constant, so any current variation that is faster than the EFC loop time > > constant will induce an uncorrectable error (at least as far as the EFC loop > > is concerned). With a separate ground pin, or a circuit designed to > > compensate for the effects of ground pin current, there will be no such > > error. > > > > Didier KO4BB > > Thanks for that explanation. > > Note thermal effects have a time constant as well. Depending > on the OCXO, or the enclosure used, it may be shorter; more > likely it's actually longer than the GPSDO time constant. This > is especially true for diurnal temperature changes where the > thermal TC is 100x to 1000x slower than the GPSDO TC! > > I understand what you're saying, though. However, in your > scenario of a more rapidly changing temperature, I suspect the > frequency changes due to the OCXO tempco itself (*internal* > resonator temperature, thermal lag(s), gradients, etc.) will far > exceed any changes in *external* EFC due to changes in oven > heater current. > > You might check this yourself by shorting the EFC pin(s) and > then run some rate dependent temperature tests. > > Another check someone could run is to deliberately place a > 1R or 10R or 100R carbon resistor in series with the EFC and > see what it takes to make this effect rise *above* the noise. > With these measured points in hand, you could then extrapolate > down to 0.01R or 0.001R (PCB trace) to see how far *below* > the noise you are in real life. > > /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.
