[volt-nuts] Reference Calibration Options - Solartron 7081andFluke 731B and 335A

Sat Sep 10 07:28:49 UTC 2011

How do you know the standards drift and not the meters ? In worst case they could drift the same amount in the same direction.
A week ago I have my 731A and 7061 calibrated against a standard cell. The fisrt days the long and short time drift was considrable. But the 731A is  now powered 24/7. Yesterday i turned on the 7061 again and it showed 1.000,006,2 V after three hours it was 1.000,000,1 V and stayed there, so keeping it powered on seems to work better.

My home made standard with out of the box cheap reference zeners, four TL431 parallel.  I have last week adjusted to 1.000,000 V on the keithley 2000. 
After a week it was 1.000,046 but I adjusted it to 1 V  again. But the reference in that has only about 150 hours burn in time total. The Short time drift is now allmost gone. It flips + 1 uV now and then, but it could be it is adjusted to 1.000,000,8 or so. 

The second one, made with an othere reference but also a standard low cost reference, a ADR421 mde to be transportable and can be powerd from anything between 6 and 12 V was adjusted to 2.500,01 on the keithley ( just stopped when the last digit flipped to 1 so I know it is as close as known as posible. ) it has not been on power this week. I put it on again yesterday and left it on for about 6 hours. It started at 2.500,01 and stayed there all the time. Weird, is the , also brand new, ADR421 so much better ?

Within a week or so i am going to order parts for the 1-2000MHz signal generator i m building, and then i want to order some better voltage references. The LM399 is not vailable. What would be the best choise ? ( I will order from Farnell) i like a reference with low tempco, so with build in heather because my lab is on the addict and temp changes can be big. From 16 to 35 dergees as extremes.

Fred PA4TIM

Op 10 sep. 2011 om 08:03 heeft "gbusg" <gbusg at comcast.net> het volgende geschreven:

> Yeah, I'm using a 732A. It's a nice box, as you know.
> 
> I'm also using a pair of Koep PN-VTS3005 10Vdc standards. Over an 8 year 
> period one Koep drifted +0.104 ppm/year; and the other
> Koep drifted +0.701 ppm/year. However the Koep's short-term noise and tempco 
> are notably worse than the Fluke 732A, so I like the 732A the best. (Wish I 
> had a 732B, but those are pricey indeed!)
> 
> I also used to have a 731B, but my particular 731B was drifting something 
> like 10ppm/year - that's still well within its 30ppm/year spec, but it 
> wasn't to my liking, so I got rid of it.
> 
> The Solartron 7081 is spec'd +/- 4.3ppm at 10Vdc/year (2nd year), so based 
> on published specs the 7081 uncertainty at 10Vdc is almost 7x better than 
> the 731B (spec'd 30ppm/year).
> 
> Not having personal experience with the 7081, I can't offer anything 
> anecdotal about it. ...So I must rely on what actual owners (of the 7081) 
> have experienced. (Have you read anything from any actual users claiming 
> that their 7081 did *not* meet the 4.3ppm/year spec at 10Vdc? ...Would like 
> to read more about that if you have any web links to comments about it?
> 
> Thanks,
> Greg
> 
> 
> 
> ----- Original Message ----- 
> From: "Charles P. Steinmetz" <charles_steinmetz at lavabit.com>
> To: "Discussion of precise voltage measurement" <volt-nuts at febo.com>
> Sent: Friday, September 09, 2011 11:22 PM
> Subject: Re: [volt-nuts] Reference Calibration Options - Solartron 
> 7081andFluke 731B and 335A
> 
> 
> Fluke specifies all outputs of the 731B at +/- 30 ppm absolute
> accuracy at 1 year, at 23C +/- 1 degree after a 30 minute warmup (+/-
> 15 ppm/90 days, +/- 10 ppm/30 days).  The 10 V outputs of the three
> that I've had were better by more than an order of magnitude -- 
> around 2 ppm/year (but note that mine were powered 24/7/365).  The 1
> V and 1.018 V outputs are significantly less stable than the 10 V
> output, but well within spec.
> 
> The 10 V output of the 732A (which I use now) is specified at +/- 6
> ppm/year (+/- 3 ppm/6 months, +/- 1.5 ppm/90 days, +/- 0.5 ppm/30
> days), for temperatures between 18C and 28C.  The ones I have do
> much, much better.  There is an interesting 1999 IEEE paper by
> Vujevic and Ilic, "Stability of Some DC Reference Standards," which
> discusses he 732A and notes that it is stable to about 0.1 ppm/year,
> which is consistent with my observations.
> 
> Given a calibration history, one can plot the expected absolute
> voltage as a function of time and get even closer.
> 
> Meters are specified somewhat differently, since there are several
> distinct error mechanisms.  My understanding is that the 7081 is
> specified as more stable than an HP3458A (which has a specified total
> error at 10 V of a bit more than 10 ppm/year, including calibration
> traceability error), but that within the cal lab community they are
> not considered to be anywhere near as stable as the HP.
> 
> Best regards,
> 
> Charles
> 
> 
> 
> 
> 
> 
> 
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