[volt-nuts] Fluke 335A

[Fred Schneider]

I measured a 731 with a scope to see the noise. It was around 25 uVpp. I think that is the most easy way. You see how much disconnected and how much it s connected. I úse a tektronix 547 with E-plugin for this. ( a lot cheaper then a 7,5 digit or more multimeter ;-)

Fred PA4TIM

Op 27 sep. 2011 om 05:04 heeft "gbusg" <gbusg at comcast.net> het volgende geschreven:

> 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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