Re: [volt-nuts] Best way to measure micro Ohms

[ed breya]

I just noticed this discussion recently, so I'm late to the party, but 
that never stops me from adding my one-cent's worth.


David, regardless of the aluminum and other material issues, I think 
your initial idea of using a lock-in analyzer is definitely the way to 
go. I'm very fond of LIAs, although I seldom need or use them, so my 
opinion is somewhat biased. I have five - two Ithaco 391A orange-band, a 
PAR 5204, an SR830 and SR850.


If you use an audio power amplifier for driving the experiment, you can 
rig it up so that the LIA can be used to measure the drive current as 
well as the resulting voltage drop. Let's say the amplifier is for 8 
ohms, so you put a few ohms in series with the output, then from there 
into a precision one-ohm sampling resistor, then into the RUT, forming a 
voltage divider. The RUT is expected to be in the micro-ohm region, 
which is many thousands of times smaller than the sampling R, so its 
tiny voltage drop will be negligible, allowing the sample voltage to be 
a good representation of the test current. You could also just treat the 
whole thing as a voltage divider and calculate the "exact" results.


The voltage on the RUT is measured at whatever gain is needed. The 
voltage on the sample resistor will be plentiful at 1V/A, and both 
signals will have very low source R, and minimal noise. Since both 
signals can be measured by the LIA, the uncertainties in assessing each 
part with different equipment are much reduced.


The reference frequency should be as low as possible, limited by the 
amplifier's low-end capability, and selected so it and its harmonics 
land as far as possible from the power line frequency and its harmonics, 
for say up to n=15, or whatever is practical. This will help to reduce 
line interference from nearby sources, and ground loops, and from the 
amplifier. Especially at low frequencies, the amplifier may show a lot 
of line harmonics when driven to high levels - the filter capacitors in 
its power supply can only do so much, and audio PAs are likely not all 
that great in terms of PSRR. Turning on the LIA's line notch filter will 
also help, at least with the fundamental.


The frequency needs to be very low in order to minimize the parasitic 
currents that will cause errors, especially considering that this setup 
is dividing on the order of a million in a single stage. If this appears 
to cause problems, you can reduce the large division ratio by using a 
much smaller sample resistor, and treating it as a divider for 
calculation purposes. Alternatively, adding some appropriate shielding, 
or splitting the division into isolated sections can greatly reduce the 
effects. To avoid signal ground loops, measuring the drive current and 
the RUT voltage should be separate operations, each carried on its own 
BNC cable to the LIA, while the other is completely disconnected and out 
of the way - having no common-grounding or cable bundling or fancy 
signal routing/switching is best. The weakest link ground-loop-wise may 
be the necessity of carrying the reference drive between the LIA and 
power amplifier input, likely sharing the same ground as the output. 
This could force you to set it up for differential measurement of the 
RUT signal. The special audio PA that I have for such purposes has its 
ins and outs transformer-coupled, which helps a lot.


This could be fun and interesting. There are plenty of pieces and 
variables involved to experiment with to optimize the measurement, and 
lots of other tricks available to enhance it if necessary.


Ed

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Re: [volt-nuts] Solartron (aka Schlumberger) 7081

[David C. Partridge]

I assume you've seen my website: 
?   The last corporate owner of 
the Solartron brand was Ametek, and their branch in Farnborough did calibrate 
them up to at least the late "noughties".  I don't know if they still do.   The 
full service manual and factory calibration instructions are on my website.

Sadly the Commodore PET software to control the calibration process was never 
released (AFAIK)?

They are easy to calibrate if you have a good calibrator (I have a 4808 which 
is now fully working).  I live in Kenilworth so not too far from  you.

Dave
-Original Message-
From: volt-nuts [mailto:volt-nuts-boun...@febo.com] On Behalf Of Dr. David 
Kirkby (Kirkby Microwave Ltd)
Sent: 26 September 2017 23:57
To: Discussion of precise voltage measurement
Subject: [volt-nuts] Solartron (aka Schlumberger) 7081

I've been offered a Solartron 7081 8.5 digit meter, but are having difficulty 
finding out much about this. Is there any "official" place where these can be 
calibrated? As far as I can see from a search of Companies House

https://beta.companieshouse.gov.uk/company/02858371

Solartron Instruments Ltd was dissolved in 2013. I don't know if there is 
really anybody able to calibrate these things.

Clearly the meter is not in the same league as a 3458A. but I've been offered 
it for little more than the cost of a new Keysight  U1282A 4.5 digit handheld 
meter! I've no idea when it was last calibrated, but I suspect long ago.




Dr. David Kirkby Ph.D CEng MIET
Kirkby Microwave Ltd
drkir...@kirkbymicrowave.co.uk
http://www.kirkbymicrowave.co.uk/
Tel: 01621-680100 <01621%20680100> / +44 1621-680100 <01621%20680100> (0900 to 
2100 UK time)

Registered office: Stokes Hall Lodge, Burnham Rd, Althorne, Essex, CM3 6DT, UK.
Registered in England and Wales, company number 08914892.
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Re: [volt-nuts] Solartron (aka Schlumberger) 7081

[Philipp Cochems via volt-nuts]

Hi,

I wouldn't say the 7081 is in the class of a HP 3458A (7081 is much
slower, much more noisy and linearity isn't as great as the HP 3458A).
But, it is definitely better than a 3457A (which is also quite noisy).

Calibration via GPIB is very simple and should be done be most
calibration labs (I've done that a few times).

Best Philipp

2017-09-27 6:17 GMT+02:00 Tom Knox :
> Hi Dave;
>
> The 7081 is a really great meter if working correctly. It is up there with 
> the Wavetek 1281, Fluke 8508, and Keysight 3458A. The only down side is the 
> front panel connector, but I have seen it converted to Banana's. I think you 
> will find it much better then the 3457A even with an upgraded reference.
>
> Cheers;
>
> Thomas Knox
> 1-303-554-0307
> act...@hotmail.com
>
>
> 
> From: volt-nuts  on behalf of Dr. David Kirkby 
> (Kirkby Microwave Ltd) 
> Sent: Tuesday, September 26, 2017 4:56 PM
> To: Discussion of precise voltage measurement
> Subject: [volt-nuts] Solartron (aka Schlumberger) 7081
>
> I've been offered a Solartron 7081 8.5 digit meter, but are having
> difficulty finding out much about this. Is there any "official" place where
> these can be calibrated? As far as I can see from a search of Companies
> House
>
> https://beta.companieshouse.gov.uk/company/02858371
> [https://d3rubtivi36dxc.cloudfront.net/images/opengraph-image.jpg]
>
> SOLARTRON INSTRUMENTS LIMITED - Overview (free company 
> ...
> beta.companieshouse.gov.uk
> SOLARTRON INSTRUMENTS LIMITED - Free company information from Companies House 
> including registered office address, filing history, accounts, annual return, 
> officers ...
>
>
>
> Solartron Instruments Ltd was dissolved in 2013. I don't know if there is
> really anybody able to calibrate these things.
>
> Clearly the meter is not in the same league as a 3458A. but I've been
> offered it for little more than the cost of a new Keysight  U1282A 4.5
> digit handheld meter! I've no idea when it was last calibrated, but I
> suspect long ago.
>
>
>
>
> Dr. David Kirkby Ph.D CEng MIET
> Kirkby Microwave Ltd
> drkir...@kirkbymicrowave.co.uk
> http://www.kirkbymicrowave.co.uk/
> Low cost Vector Network Analyzer Calibration 
> kits
> www.kirkbymicrowave.co.uk
> How to buy our calibration kits. Can we pay in $(USD) or € (Euros)? Kirkby 
> Microwave 85033 7 GHz SMA Kirkby Microwave 85033 option 001. 7 GHz SMA with 
> reverse ...
>
>
> Tel: 01621-680100 <01621%20680100> / +44 1621-680100 <01621%20680100> (0900
> to 2100 UK time)
>
> Registered office: Stokes Hall Lodge, Burnham Rd, Althorne, Essex, CM3 6DT,
> UK.
> Registered in England and Wales, company number 08914892.
> ___
> volt-nuts mailing list -- volt-nuts@febo.com
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> volt-nuts Info Page - American Febo 
> Enterprises
> www.febo.com
> volt-nuts is a low volume, high SNR list for the discussion of precise 
> voltage measurement and related topics. To see the collection of prior 
> postings to the list ...
>
>
> and follow the instructions there.
> ___
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Re: [volt-nuts] Solartron (aka Schlumberger) 7081

[Tom Knox]

Hi Dave;

The 7081 is a really great meter if working correctly. It is up there with the 
Wavetek 1281, Fluke 8508, and Keysight 3458A. The only down side is the front 
panel connector, but I have seen it converted to Banana's. I think you will 
find it much better then the 3457A even with an upgraded reference.

Cheers;

Thomas Knox
1-303-554-0307
act...@hotmail.com



From: volt-nuts  on behalf of Dr. David Kirkby 
(Kirkby Microwave Ltd) 
Sent: Tuesday, September 26, 2017 4:56 PM
To: Discussion of precise voltage measurement
Subject: [volt-nuts] Solartron (aka Schlumberger) 7081

I've been offered a Solartron 7081 8.5 digit meter, but are having
difficulty finding out much about this. Is there any "official" place where
these can be calibrated? As far as I can see from a search of Companies
House

https://beta.companieshouse.gov.uk/company/02858371
[https://d3rubtivi36dxc.cloudfront.net/images/opengraph-image.jpg]

SOLARTRON INSTRUMENTS LIMITED - Overview (free company 
...
beta.companieshouse.gov.uk
SOLARTRON INSTRUMENTS LIMITED - Free company information from Companies House 
including registered office address, filing history, accounts, annual return, 
officers ...



Solartron Instruments Ltd was dissolved in 2013. I don't know if there is
really anybody able to calibrate these things.

Clearly the meter is not in the same league as a 3458A. but I've been
offered it for little more than the cost of a new Keysight  U1282A 4.5
digit handheld meter! I've no idea when it was last calibrated, but I
suspect long ago.




Dr. David Kirkby Ph.D CEng MIET
Kirkby Microwave Ltd
drkir...@kirkbymicrowave.co.uk
http://www.kirkbymicrowave.co.uk/
Low cost Vector Network Analyzer Calibration 
kits
www.kirkbymicrowave.co.uk
How to buy our calibration kits. Can we pay in $(USD) or € (Euros)? Kirkby 
Microwave 85033 7 GHz SMA Kirkby Microwave 85033 option 001. 7 GHz SMA with 
reverse ...


Tel: 01621-680100 <01621%20680100> / +44 1621-680100 <01621%20680100> (0900
to 2100 UK time)

Registered office: Stokes Hall Lodge, Burnham Rd, Althorne, Essex, CM3 6DT,
UK.
Registered in England and Wales, company number 08914892.
___
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volt-nuts Info Page - American Febo 
Enterprises
www.febo.com
volt-nuts is a low volume, high SNR list for the discussion of precise voltage 
measurement and related topics. To see the collection of prior postings to the 
list ...


and follow the instructions there.
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