Another AC voltage standard

[MosherIV]

Hi

There are numerous projects around now building DC voltage references based on the AD584 (or other precision voltage reference)
Dave himself has done a couple of videos on precision current sources.

There are very few projects to build an AC voltage reference.
I found this one but no one came up with a design :
https://www.eevblog.com/forum/projects/diy-ac-voltage-reference/

It is also interesting to read how Fluke have done it :
https://www.eevblog.com/forum/repair/fluke-5200a-ac-voltage-calibrator-teardown-and-repair/

I have also been engaging with the volt nuts :
https://www.eevblog.com/forum/metrology/true-rms-converters/
(I did hijack the thread - sorry )

So, here is my attempt at an AC voltage standard :
It is based on a low drift 32.768KHz crystal
http://cpc.farnell.com/iqd-frequency-products/lf-xtal025159/crystal-quartz-smd-32-768khz/dp/SC10066?aa=true&vw=&selectedCategoryId=&categoryId=700000011705&eq=N%3D213497%2B411%26amp%3BNs%3DP_STORE_MARKETING_RANK_FARNELL_CPC%257c0%257c%257cP_MAN_PART_NUM%257c0%26amp%3BNtpc%3D1%26amp%3BNtpr%3D1&searchView=table&iscrfnonsku=false
Basically, the design amplifies the crystal oscillation to 12p-p and then uses voltage divider to get the 4 output levels.
The divider will use this series of high precision, low drift resistors
http://cpc.farnell.com/webapp/wcs/stores/servlet/Search?catalogId=15002&langId=69&storeId=10180&categoryId=700000011452&eq=N%3D219764%2B411%26amp%3BNs%3DP_STORE_MARKETING_RANK_FARNELL_CPC%257c0%257c%257cP_MAN_PART_NUM%257c0%26amp%3BNtpc%3D1%26amp%3BNtpr%3D1&showResults=true&aa=true&pf=110075262&vw=
(One concern is the calibration pot for initially setting the gain to get exactly 12Vp-p - any comments ? )
Each of the outputs is buffered by a unity gain op-amp, again a high precision, low drift OP07

The design also provides a 5Vp-p output for testing non TrueRMS AC meters.
The output should be 5V precisely due to the 5V regulator being derived from a precision 5V reference (LM336 shown but could go to something like a REF02)

So, any thoughts, comments please?

[Vgkid]

For your 12vpp signal would it be a sine or square. For the square wave pirtion of your signal it would be interesting to see if the  5v input is still 5v on the output. Wouldn't matter as much if this was for an o-scope.

[MosherIV]

For your 12vpp signal would it be a sine or square.

Sine. The crystal should produce something very close to a sine wave, which is then amplified up to the 12Vp-p

For the square wave pirtion of your signal it would be interesting to see if the  5v input is still 5v on the output

Are you referring to a possible output drop by the 74HC00 ?

[Vgkid]

You might want to check the specs of your meters. I'm not sure if 32khz is too high of a frequency. Most are specced for audio frequencies, or lower.

[MosherIV]

Hi vgkid

You are right
Oh well back to the drawing board.