[volt-nuts] Traveling Standards - Measuring Protocol

[Andreas Jahn]

> Also very useful to measure the actual Temperature Coefficient of the
> devices so that the temperature readings have more meaning.
>
> When evaluation precision voltage references,
> I find it very helpful to make a High Resolution strip chart recording, be
> it Analog or Digital,
> Preferable showing Both temperature and voltage.
> For an example of how I get much better than 0.1 PPM resolution using 50
> year old technology,
> See attached plot comparing two 10 volt devices, using a slow, dual 
> channel
> analog Rustrak recorder and Fluke 845A/B null meter
>

Tempco measurement will be essential for the MAX6350.
For the LM199 I have made the experience that over a
10 to 40 degree (celsius) temperature range there will be
around 1 ppm of change. Of course its better to know
the exact values. So its easier to trace back the current measurement.


First picture MAX6250A (which is similar to the MAX6350)
used as voltage reference of a LTC2400 measuring
my LM399 #2 with a LTC1043 based precision voltage divider
over temperature range 10 - 40 degree celsius.
Y-axis is 2:1 divided voltage in mV.
You can clearly see the hysteresis of the plastic device.
And you can see a "hysteresis jump" near 39 degrees of around 1 ppm.

Attached you see a plot of my LM399 #2 over temperature
as difference to my LM399 #1 at room temperature.

recorded is
red: difference voltage in mV LM399 #1 - LM399 #2
light blue: same but averaged to get the noise out
green: environment temperature of LM399 #2 housing
dark blue: within LM399 #2 housing
yellow: environment temperature of LM399 #1

so the change is around 7uV when regarding the averaged value.
and most of the "tempco" seems to be off the temperature
gradient (thermo voltages) and not from the actual temperature.


With best regards

Andreas
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