[time-nuts] HP5065A environmental sensitivities

[Magnus Danielson]

Wulf,

On 05/19/2016 11:04 AM, DG2OM at gmx.de wrote:
> 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.

If you have an open loop measure of your clock and pressure, then fit 
the pressure variations over the full data set and produce a corrected 
value for the full dataset, then this troublesome as you now have used 
the samples after the beginning to affect the beginning. You have 
provided feedback and correction. This is useful to show potential of 
such correction.

If you only used one dataset for match the coefficient and then use a 
new dataset to correct using the new pressure data and the coefficient, 
then that will be more representative of real-time performance even if 
you do it as batch-processing as an after the fact setup.

What you want to do is to look at the corrected curve and see if there 
is any other terms, that can be quadratic, differential or integral 
variants (just to give you some ideas) of the pressure data and that may 
be a hint about further improvements of the model that allows even 
better compensation model.

> 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.

The model should always be verified so that major components is found.
The proportional component seems strong thought.

> 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.

Humidity and pressure play a role with surrounding temperature in 
cooling in that it they will shift the thermal resistance through which 
the cooling of the ovens goes, either being higher increase the 
conductance, and varies the load of the oven which will not perfectly 
match the load and hence the temperature varies.

> 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.

Pressure compensation is an interesting approach, thanks for 
illustrating it!

Cheers,
Magnus