Fluke Calibration | RATIO Mode explained for 8846A and 8508A Reference DMM

[Kiriakos GR]

For us regular mortals, Fluke Calibration role this is visualized, as some one with a wrench key in hand, he is testing and adjusting a DMM, so this to measure correctly. 

Under the hood, Fluke Calibration this is involved at exploring electrical metrology, and at developing special tools for metrology.
In our planet, FLUKE 8846A and 8508A Reference DMM, they both share a special function, and this is RATIO mode.
   
The problem begins, when Fluke Calibration work as solutions developer, this gets documented by FLUKE Corporation team, when the last team is responsible to offer documentation for consumer related products.

I have now proofs, that significant portion of information this gets lost, and or were skipped from be documented, because FLUKE marketing team this worked as a Low-Pass filter.

RATIO Mode, this is a tool for metrology, and for DCV sources comparison.
Fluke 8846A this designed including this function, RATIO this is a high resolution comparator.
Due this RATIO mode, and at 100 PLC, 8846A this using it max internal resolution of 8 1/2 digits, and it can resolve or measure DC signal down to 1ppm.
VFD display appearance at 1ppm this looks as  001.000
001 this is actual mathematical measurement
While 001.000 this is a metrology level of digits resolution. 
For example  000.999 this translates that you are very close and below the 1ppm.
Regarding 8846A measuring uncertainty, at 100mV DC range, this is within specification, and even if you measure as low as 1ppm, you may trust the measurement.   

The larger brother, 8508A Reference multimeter.
This can resolve or measure, down to 0.1ppm

Entire pack of 8846A related documentation, this does not offer a single word, of how some one to use RATIO mode, in a productive way.
Thanks to Fluke Calibration, and due a specific Application Note
( Maximizing your reference multimeter, minimizing measurement uncertainties )
U.S.A. 9/2011 2090893C D-EN-N
Pub-ID: 10757-eng   

I were able to get relative information's.   
I am offering this as download, to ITTSB visitors.
FLUKE Corporation this is a business, we cannot stop them from discontinuing old products.
But regarding conservation of essential knowledge, this is something that I can momentarily assist, for as long ITTSB.EU this is still standing.

[overvolt]

Just for sanity check, is this thing measuring now almost 286 ppm ?  (8846A screen shot )

[Kiriakos GR]

YES    

Another undocumented find is the appearance of m on the display.
AI explanation
Why the meter shows "m"

The Fluke 8846A display automatically scales the units to keep the most significant digits visible.
In the RATIO mode:
If the ratio is 0.285..., it displays 285.884 m  (= milli-units) which represent the ratio of two different noise floors.
If the ratio were 0.000285..., it would likely scale down further to 285.884 (Greek μ = micro-units).

If you wanted to express that specific ratio in ppm:
0.285884 x  1,000,000 = 285.884 ppm

6.5-Digit Precision: The meter always shows six decimal places of information regardless of the prefix,
which is why it can resolve changes as small as 1 ppm (the last digit on the micro-units)


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Christopher L. Grachanen | Transcat Director of Metrology (2019)

RATIOING EVALUATION
Another series of evaluations focused on 8588A ratioing two independent measurements.
Ratio is a measurement technique where the DMM makes two related measurements over a short time.
It is intended for use to test or calibrate similar parameters such as when a known standard is compared to an unknown (such as two resistors,
or two voltages).
As such, the measurements made are strictly relative, one measurement compared to another, and the resulting ratio comparison has very small
uncertainty versus a traditional individual measurement of the unknown parameter needing to be measured.

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At my test, I am comparing two unknown DC sources, output expected be EMF.
Its more an test, than a measurement, 8846A this is used as a differential voltmeter.
In other words, I am using RATIO as EMF sensor (this calculating the ratio of thermal offsets).