Cheap low effort voltage reference ~20ppm

[gbaddeley]

Hi, I've been into electronics for a very long time, but new to EEVblog. I hope some kind soul can help with my query.
I want to check the accuracy of DC voltage readings on my vintage Fluke 8375A to say 20ppm of true at a known temperature. I would also check my other DMMs and a vintage Keithley differential voltmeter.
What are low cost / low effort / entry level voltage references that will give me a reasonable idea of accuracy at 20ppm, without going to a cal lab?
Buy or build? 10 Volts or something else?
Cheers, Glenn (Melbourne AU)

[The Soulman]

You might wan't take a look here:

https://www.eevblog.com/forum/metrology/best-out-of-the-box-10v-reference/

[Kleinstein]

One of those relatively cheap 10 V reference boards from china are probably a good bet. The bad thing is that not all sources are reliable and the give values have a small chance to be fake - so one might need a 2 nd (different source) to be reasonably sure. Still 20 ppm error might be possible from the meters used to measure the quoted values.

I am not aware of Ref chips with better than 20 ppm absolute accuracy. Chances are the effect of soldering them could be larger than that.

[rhb]

I bought a DMMCheck Plus from Doug Malone at voltagestandard.com.  That's out of stock but he has the 30 ppm  VREF10-003 in stock for $53 US.  I'm quite tempted to get one myself.  That's a low cost cal.

Doug has an in cal 3458A he uses to check and adjust things before shipment and ages his references before shipment.