Dave, the title is: Thermal Voltage Converters and Comparator for Very Accurate AC Voltage Measurements by E.S.Williams.
Adrian > Gesendet: Montag, 25. August 2014 um 19:32 Uhr > Von: "Dave M" <dgmin...@mediacombb.net> > An: "Discussion of precise voltage measurement" <volt-nuts@febo.com> > Betreff: Re: [volt-nuts] AC calibration > > Adrian, > Do you have a link or title for the NIST paper that you mentioned? > > Dave M > > > acb...@gmx.de wrote: > > fred, > > generally you raise a good point, I had the same issue of calibrating > > an ac voltage to a high level of accuracy. you need this e.g. to > > validate the self.cal of a 3458a or other precison stuff like the > > 8506a0. > > > > what i would recommend to do if you want to keep costs down is: > > in a nutshell, get a thermal converter in the lowest range you need > > and a second one on range above. build a set of resistor range > > extenders (rf type with appropriate connectors and housings) to > > expand the range to where you need to be max. get one of the thermal > > converter calibrated (the higher one usually, and you need to havr > > good cal lab, should be <10ppm accuracy) and use it to calibrate the > > rest. generally, up to 20khz, the accuracy is some 20 ppm anyway for > > thermal converters! at higher frequencies, due to reflections and > > stray capacitance/inductance influences, the accuracy decreases. the > > resistor range extenders though, if build up correctly, only have a > > few ppm impact (there is a paper from nist on that, but this is only > > typical). you can calibrate all converters to the one you got > > externally calibrated. do some research in the web, when you do the > > calibration, you need to determine the so-called constant N. then do > > an ac, dc+, ac, dc-, ac measurement between the the two and establish > > the deviation, also establish the error propagation. the end result > > will be a set of highly precise (low inaccuracies9 thermal converters > > good enough to calibrate a 3458a an better devices. if you want to > > spend the money, you could also buy a set of converters/range > > resistors (with/without a 540), that typically is a few k altogether, > > while a single device sometimes is available for below 100 bucks. you > > need to have a stable 7.5 digit nanovoltmeter though for the > > measurements of the tvcs (34420a or 2182 typically ) and precision > > (stable) dc and ac sources. but in the end, all you need is a single > > calibrated thermal converter. > > > > adrian > > > > > > > >> Gesendet: Montag, 25. August 2014 um 18:38 Uhr > >> Von: "Dave M" <dgmin...@mediacombb.net> > >> An: "Discussion of precise voltage measurement" <volt-nuts@febo.com> > >> Betreff: Re: [volt-nuts] AC calibration > >> > >> Well, you sort of answered your own question. The equipment is > >> called a Thermal Transfer Standard, but instead of thermistors, it > >> uses a thermocouple. Look at the manual for the Fluke 540B > >> (http://bama.edebris.com/manuals/fluke/540b/) and you'll see how > >> it's done. Basically, the AC source is input into the transfer > >> standard, and the standard's internal reference voltage is adjusted > >> for a null on the galvanometer. Leaving the reference voltage > >> setting alone, a DC voltage is input into the unit, and the DC > >> source is adjusted for a null on the galvanometer. At that point, > >> the AC voltage source is equal to that of the DC voltage source. > >> > >> Ther are thermocouple-type thermal converters used for RF voltage > >> measurements with the transfer standard. They aren't cheap, and you > >> have to have a converter for each range of voltages that you need to > >> measure. The thermal converters used with this type of transfer > >> standard isn't great (50 MHz or so typical), but their accuracy far > >> surpasses that of the thermistor type sensors. > >> > >> There are other brands and models of thermal transfer standards, but > >> I have a Fluke model 540 and a few thermal converters. That's why I > >> referred you to the manual for it. > >> > >> Cheers, > >> Dave M > >> > >> > >> pa4...@gmail.com wrote: > >>> Is there a way to link an AC voltage to a DC source for compare. I > >>> can check my calibrators (like a Fluke 332, 760 , 731 and a Philips) > >>> against standardcells. But for AC I can not do that. I have two > >>> AC+DC TRMS 7,5 digit meters but the last calibration was 2 years > >>> ago. > >>> > >>> My idea is in theory simple. It is based on the thermal converters > >>> used in RF powermeters. Two resistors, two high resolution > >>> temperature meters. AC on the first en DC on the second. If both are > >>> the same temperature the AC voltage is the same as the DC voltage. > >>> But I'm sure some people here have done this in the past. I would > >>> like to use it for 50 to 100 kHz (or less) and something like for > >>> 1V, 10V and 100V (and use several resistors/heaters.) > >>> > >>> Or mabey there is an other way to convert AC (for RF it can be done > >>> with lightbubs but I never tryed that) I do not mind if it is slow > >>> etc, I like this sort of experiments. You can learn a lot from it. > >>> > >>> Fred, pa4tim > >> > >> > >> _______________________________________________ > >> volt-nuts mailing list -- volt-nuts@febo.com > >> To unsubscribe, go to > >> https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts and follow > >> the instructions there. > > _______________________________________________ > > volt-nuts mailing list -- volt-nuts@febo.com > > To unsubscribe, go to > > https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts > > and follow the instructions there. > > When the people fear the government, there is tyranny. When the > government fears the people, there is liberty -- Thomas Jefferson > > > Dave M > > _______________________________________________ > volt-nuts mailing list -- volt-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts > and follow the instructions there. _______________________________________________ volt-nuts mailing list -- volt-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts and follow the instructions there.