Some answers to comments: Magnus, I don’t think I have made a closed loop. It works like UTC for poor man. I gathered data from different master clocks and from a weather station and produced a new software corrected time scale for my own. But you are right. The correction is the best fit for this specific data-set and will be worse if applied to another. The ADEV plot should be clipped to trusted values - maybe 500000 sec. I intend to apply a hardware compensation. Therefore I was happy to find a barometric pressure sensor 144SC0811-Baro at an auction side some weeks ago for less than one tenth of the normal prize. Approximate 240 kOhm should be needed from the output of this module to the base of Q6B for compensation.
James, when I made the correlation the best fit was obtained comparing a frequency difference data-set delayed 1 hour to the pressure measurements. But I have to dig into the data-set again – there might be an error calculating the MJD from Middle European Time. As far as I understood from Corby´s measurements, the frequency reacts immediately to a pressure change without delay. For the compensation, a delay does not matter very much. Pressure changes are normally very slow. Poul-Henning, The measurement is made in normal environment. Temperature measurements of the Thunderbolt, which was two meter away, show daily variations of 1-2 degree C and an additional drop of 2 degree during the weekend. Humidity measurements are not made. Temperature effects as well as aging are still left in the residuals of my data. The aging of this specific instrument is nearly zero. The frequency was adjusted 6 month ago and the drift is less than 1E-12 during this time. Bjørn, I have the temperature measurements inside the Thunderbolt and temperature measurements from a temperature Data-logger placed inside the HP5065A. This datalogger has a temperature resolution of around 0.4 degC. Attila, I know the SHT11 from the old days when a LPT-port could be controlled by the user. It is a nice device. But I bought the 144SC0811 which can be used by adding only one resistor. Corby, It would be nice to see the results with temperature compensation. There are lots of sources producing temperature sensitivity. All have a different time constant. AS Poul-Henning found out, the rate of temperature change is the worst problem. In my eyes temperature compensation is much more complicated then compensation for barometric pressure. Best regards Wulf Oelschlägel _______________________________________________ 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.
