[volt-nuts] Fluke 335A

[J. L. Trantham]

Greg,

Are there sources 'known to be quite'?  Any way to make them quite?

How about a standard D cell battery?  With a filter capacitor?  I suspect it
will have a slow downward trend but how about ripple and noise?

Do any of the 'volt-nuts' have a favorite source to measure when looking to
see how 'stable' their DMM is?

I'll have to go back and look at the manual for the 335A about the Ripple
and Noise spec.

Thanks,

Joe

-----Original Message-----
From: volt-nuts-bounces at febo.com [mailto:volt-nuts-bounces at febo.com] On
Behalf Of gbusg
Sent: Monday, September 26, 2011 10:05 PM
To: Discussion of precise voltage measurement
Subject: Re: [volt-nuts] Fluke 335A


Hi Joe,

My calculations agree with yours, as far as Fluke specs for your two 
voltages are concerned.

Fluke spec'd Ripple and Noise (all frequencies) as <20 uV rms on the 10V 
range. So that would be another 2ppm rms adder for 10Vdc setting, 20ppm rms 
adder for 1Vdc setting and 200ppm rms adder for 100mVdc setting. But I'm not

immediately sure how that rms noise spec might translate to observed 
racking-around on your 3478A (depending on integration time setting on your 
3478A, etc.).

Fluke's basic 10 uV adder (for 10Vdc range) translates to 1ppm adder at 
10Vdc setting, 10ppm adder at 1Vdc setting and 100ppm adder at 100mVdc 
setting. The way I look at it, that 10 uV adder accounts for some short-term

instability (which might also show up as some racking around on your 3478A) 
plus DC zero offset (as observed on your 3478A).

Anyway, obviously the 335D "likes" full (or near full) scale the best.

You could test your 3478A short-term noise (racking around of readings) by 
using it to read a source that's known to be very quiet. Or at least you 
could build a 10 to 1 or 100 to 1 resistive divider between 335D and your 
3478A to see if that reduces the observed noise.

Best,
Greg


----- Original Message ----- 
From: "J. L. Trantham" <jltran at att.net>
To: "'Discussion of precise voltage measurement'" <volt-nuts at febo.com>
Sent: Monday, September 26, 2011 8:39 PM
Subject: Re: [volt-nuts] Fluke 335A


Greg,

If I understand the spec's correctly, the accuracy at 10.000000 Volts is +/-
30 uV (+/- (0.002% of setting + 10 uV)).  At 0.123456 Volts, it would be +/-
12.5 uV.  The stability spec is +/-(0.001% of setting + 10 uV) per month or
11.23456 uV.  I think I am within those specs.

However, I did not see a 'noise' spec.

The question is how stable should the reading be when watching it on a DMM?
Mine fluctuates about 3 uV over about 2 seconds (on an HP 3478A at nominal
settings).  Is that normal?  I am hoping someone with a 335A or D will be
able to look at theirs and tell me if what I am seeing is reasonable or do I
have more work to do to obtain better stability/lower noise.

It ultimately boils down to what to trust, the meter or the standard.  You
know the old saying, 'a man with one volt meter......'.

Thanks,

Joe



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