[volt-nuts] AC calibration

Steve - Home steve-krull at cox.net
Wed Aug 27 09:37:08 EDT 2014 

Fred,

The 3458A is 8.5 digits, which puts it into the standards category. They are used as lab standards in many, many labs. 

73,

Steve
WB0DBS



> On Aug 27, 2014, at 12:08 AM, <pa4tim at gmail.com> wrote:
> 
> Thanks, I did not new NIST has so much interesting information on their site. 
> 
> 
> 
> 
> I read the following on their site :
> 
> "multirange instruments with up to eight decimal digits of adjustability, are not considered by NIST to be standards "
> 
> 
> 
> 
> Does that mean a HP3458 ? Fluke in the Netherlands used a HP-3458 and a 732 to calibrate the Fluke 5101 that  I'm working on at this moment (it failed calibration due to some hardware faults) 
> 
> 
> 
> 
> Everybody thanks for the information. Turns out, a friend has a GR 1455AH for me, that is some kind a AC KV divider. 
> 
> I will test if the output of my HP 3400 is usable to connect a DMM. I have one I restored a few years ago. Besides that someone mentioned to look at the LT-1088.  
> 
> 
> But that has to wait until I have some more time. I only repaired calibration, percission gear and RF stuff  for my hobby, but, not planned, I started to do this on a commercial base too. See my (non commercial) site about my collection calibration and other gear and projects  www.pa4tim.nl .
> 
> Today the 5101 goes back to the custommer but he brings 2 other instruments in need of some TLC and a precheck before they are shipped to Fluke for calibration.  And yesterday an other company asked if I want/can repair a G&M safety tester (a sort of megger on steroids) that died during calibration.  
> 
> 
> Fred
> 
> 
> 
> Verzonden met Windows Mail
> 
> 
> 
> 
> 
> Van: acbern at gmx.de
> Verzonden: ‎dinsdag‎ ‎26‎ ‎augustus‎ ‎2014 ‎18‎:‎56
> Aan: volt-nuts
> 
> 
> 
> 
> 
> 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" <dgminala at mediacombb.net>
>> An: "Discussion of precise voltage measurement" <volt-nuts at 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
>> 
>> 
>> acbern at 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" <dgminala at mediacombb.net>
>>>> An: "Discussion of precise voltage measurement" <volt-nuts at 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
>>>> 
>>>> 
>>>> pa4tim at 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
>>>> 
>>>> 
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>> 
>> When the people fear the government, there is tyranny. When the
>> government fears the people, there is liberty -- Thomas Jefferson
>> 
>> 
>> Dave M
>> 
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