Electronics > Metrology

Kalibrierlabor - Calibration LAB

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Kjelt:
Just a question i know that the si standard meter is kept somewhere in a vault.
What was used as the standard for Voltage before 1990 when the josephson junction was degined, is that some chemical cell somewhere?
Can we build something similar?

zlymex:

--- Quote from: Kjelt on September 20, 2016, 09:52:46 pm ---Just a question i know that the si standard meter is kept somewhere in a vault.
What was used as the standard for Voltage before 1990 when the josephson junction was degined, is that some chemical cell somewhere?
Can we build something similar?

--- End quote ---

Standard cells were used before JJ Arrays.
http://digicoll.manoa.hawaii.edu/techreports/PDF/NBS84.pdf

Kjelt:
Thanks, I had hoped it would be relatively simple to create such a standard Weston cell but reading that pdf we have to deal with very poisonous chemicals which are hard to obtain. Oh well another idea down the drain  :-[

--- Quote ---Only four materials are required. These are mercury, cadmium,
sulfuric acid, and water, all of which may be puri
fied by distillation. To these four materials may
be added a fifth, CdSO4 8/3 H 2 O, to avoid preparing
it from cadmium and sulfuric acid; it may be puri
fied by repeated crystallizations from conductivity
water.
--- End quote ---

Gyro:
I'm playing with a saturated Weston cell at the moment:

https://www.eevblog.com/forum/metrology/muirhead-std-and-ref-cells-all-catalogue-info-uploaded-!-(ayce)/msg1030098/?topicseen#msg1030098

The conclusions so far:

- Initial 0.01% tolerance
- They make very good thermometers and need a good temperature controlled enclosure... or one with high thermal mass and an accurate thermometer.

Chris

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