[volt-nuts] AC Voltage Measurement Standards
acbern at gmx.de
acbern at gmx.de
Thu Jul 10 18:55:23 EDT 2014
I have a set of 7 TVCs, from 1 to 100V. having them all calibrated externally is just too expensive. There is no doubt that having all 7 TVCs calibrated at NIST or PTB, wherever you are, is much more precise, I will just not spend it and live with the accuracy I get.
As source I am using a Datron 4808, as nanovolt meter an Agilent 34420. Problem with this is, you pointed it out, Agilent does not specify transfer accuracy, I am in contact with them, so far no outcome though, not sure there will be any. So I have not yet completed my error calculation for the TVC cal. I will probably end up doing some calculations based on data sheet an then vaildate by measurement. Need that on the 10mv range only, so effort is limited. additionally I also have a ratio transformer, which is good to about 10kHz, that also allows for validating the TVC results by comparison in lower frequency ranges and narrow down the tolerances.
I do have a 182-M, but do not trust it, I saw a lot of drift doing some other measurements although it passes performance verification, and I just got a 2182, which has an issue that needs to be fixed first. I need to say the 34420a is very stable with the digital filter switched on and you can see the nanovolts walk until the TVC stabilizes. vice versa, if you have an issue in the setup (thermal drifts...), you also seethat very well, so the filter is not hiding this.
as far as your comment re. calibrating a set of resistor cal from one calibrated one, whats wrong with it? if you do that with a stable voltage and by voltage divider measurement using the linearity of the 3458A, you end up with pretty decent accuracies. I cannot comment on the 242, just did some quick checks some time ago and my quick assessment then was it is worse/not better than the 3458a method.
> Gesendet: Mittwoch, 09. Juli 2014 um 16:35 Uhr
> Von: "Todd Micallef" <tmicallef at gmail.com>
> An: "Discussion of precise voltage measurement" <volt-nuts at febo.com>
> Betreff: Re: [volt-nuts] AC Voltage Measurement Standards
> I would like to know more about your setup. Which source(s) are you using
> for the input and which nanovoltmeter(s) are you using to transfer the 10V
> TVC to your other converters? I remember you asking on PMEL forum about the
> accuracy of using a 34420A nanovoltmeter. I did not see a response as to
> whether you opted for an alternative like Keithley 2182(A) or a low noise
> preamplifier connected to a 3458A.
> I have done some reading about how NIST transfers their calibrations using
> two TVC's in parallel and I am guessing that is what you are doing.
> To transfer the accuracy up/down to other TVC's at different rated voltages
> appears to be a difficult task since they typically need at least half the
> rated max voltage to be within spec. It would be similar to starting with a
> SR104 standard and transferring its value through a set of SR1010 and
> SR1050 resistors using an ESI 242.
> I have a few AC sources, and I would like to be able to verify my TVC's
> without sending all of them out for cal. Ballantine quoted $600+ per TVC
> and I haven't checked what Fluke would charge for each A55.
> I personally did the following: I got a Ballantine 1605A transfer
> > voltmeter. This is comparable to the 792A in a way, except it was much
> > cheaper. It is automatic, much easier to use than the Fluke 540 and goes up
> > to I think 100MHz. This can be used for percision calibrations as a working
> > standard. The calibration of this meter as well as others (e.g. the 3458A
> > in its AC mode) I am doing with a set of thermal converters (0.5V to 100V).
> > One of which (10V) has been externally calibrated up to 30MHz, cal of the
> > others are derived from it. That way I am deriving everything from a very
> > precisely (few ppm) calibrated 10V TVC. Overall, this saves cost on the
> > calibration side, allows for high accuracy and measurement speed is good.
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