Electronics > Metrology

ADR1001 - Ovenized Voltage Reference System

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I think I have to rethink :D my power supply in the box. Currently I've been using AC w/ the transformer - I chose a small EI core trafo with split bobbins for primary and secondary, no shielding. It seems to me the capacitive leakage is still there (even I see no diff here with my 34401A - w/ or w/o an additional isolation transformer made of two b2b tranformers). While watching MarcoR'es video on "the extreme isolation" it is clear it affects the measurements and the meters may react differently on a common mode leakage. Most probably I would add a connector on the box for an external Li_ion (5S) bypassing the trafo during the measurements (the trafo will work during aging only).
PS: the video YT/watch?v=9JinSfCKuNQ
PPS: how to add a link to an YT video such it will not start to play here??

In my ADR1399 setup the transformer is external, as well as recitifier, capacitors and linear regulation pass transistor, as its heat production is affected by mains voltage variations. Opamp and resistors of the supply remained inside the box. Everything in the box runs from a constant 20 V supply voltage derived from the 10 V precision output.
I think the ADR1399 works better with 20 V for the heaters.
I also want to add as backup a lithium ion pack that i bought at the local discounter (meant for handheld drill/screw driver).

Regards, Dieter

I modded the box a little bit - the front panel post for the internal Vcc measurement is now external battery input (via a diode). I made an overnight measurement with 20V ext battery and the temperature inside the sandwich dropped by aprox 1.5C (against the AC powering where the transformer generates some heat). That T_board drop may result in aprox +2.2uV increase at the same ambient. In my box the PSU part (in the back of the box) is in "open air" (there are the vent slots in the top/bottom walls), the reference sandwich is isolated with foam (in the front of the box).

An update:
In order to create more confusion - here are both graphs - with "my TC compensated 34401A" and with "the raw 34401A" data.

An update: with the higher ambient the measurements get more hairy :)
PS: I've been using +0.5ppm/C for the TC_DMM compensation, the latest "statistics" shows it should be 0.47ppm/C, what is rather small difference considering the behavior of the 399 inside the DMM (the typical random walk of the 399 is within 1ppm during an overnight measurement)  ::)


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