Electronics > Metrology

#1000: My (hi)story of the Weston cell, of the Volt, and of being a volt-nuts

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imo:
Infected by this topic I got my first black box:

Muirhead D-845-D
Reference Cell
No: 459872

I did a measurement immediately after its arrival (34401A in HighZ) and got 1.018418V. That is on the low side from what I see here. It was shaken during the transport and also it was pretty hot outside, so the voltage will change a little bit after the cell stabilize itself, imho.
Is there a chance to estimate the production date based on the serial number?

grizewald:
This is my Muirhead D-402-A Standard Cell - A saturated Weston cell in a beautiful black Bakelite case which I picked up from eBay several years ago. It was a bit of a gamble really, probably totally illegal to ship and when I went to collect it from my local post agent, I wasn't looking forward to having to tell them that they needed to call a hazmat team if I could see that the package was wet.



Thankfully, it survived an international journey through the postal system. I can see a few drops of mercury on top of the cadmium sulphate crystals in the negative leg, but other than that, it is unscathed. These particular cells were designed to withstand being transported in any orientation, given suitable packaging, so it's not really that surprising that it was still OK.



The cell itself is just two years younger than I am and is probably in significantly better condition!



From time to time, I measure the cell voltage with my calibrated 7.5 digit Solartron meter and the reading is usually around 50µV higher than the temperature adjusted expected reading and well within the meter and cell's specifications. The thermometer that I keep in the thermometer hole in the cell's case isn't calibrated, so there is also some uncertainty in my calculation of the temperature adjusted voltage.

It has shown no signs of the voltage changing during the just over three years it has been in my possession, so even after some 55 years, it is still performing remarkably well! The latest entry in my log is:

Date         Temp    Expected   Actual     Delta
2022-05-22   25.25   1.018351   1.018400   0.000049

While it might be more useful these days as a thermometer rather than a voltage reference, it's still a great piece of history which I am very happy to own and I'm amazed that it still seems to work just as well as it did when it was new.

tggzzz:

--- Quote from: grizewald on August 09, 2022, 08:33:39 pm ---This is my Muirhead D-402-A Standard Cell - A saturated Weston cell in a beautiful black Bakelite case which I picked up from eBay several years ago. It was a bit of a gamble really, probably totally illegal to ship and when I went to collect it from my local post agent, I wasn't looking forward to having to tell them that they needed to call a hazmat team if I could see that the package was wet.

--- End quote ---

I used that to beat my supplier down in price to £0 (but maybe £5 for a couple of D-402-Bs, some Na, some Mg, some KMnO4, and some NaClO3. A local 16-18yo college was shutting and selling off all its contents. A local clearance company was dealing with it, and the young girl knew a bit about disposing of hazardous materlals.

I gave them a reasonable but low price for a couple of very useable stereo microscopes; normally I can't stand the things. I also gave them tips about flogging boat anchors that didn't interest me. (That was back in 2016, before I became a *nut, abd before the TEA thread had exposed/developed our vices)


--- Quote ---Thankfully, it survived an international journey through the postal system. I can see a few drops of mercury on top of the cadmium sulphate crystals in the negative leg, but other than that, it is unscathed.

--- End quote ---

See pictures of mine in reply #35 :)


--- Quote ---These particular cells were designed to withstand being transported in any orientation, given suitable packaging, so it's not really that surprising that it was still OK.

--- End quote ---

I haven't seen any info to that effect, but that is absence of evidence, not evidence of absence. Any refs?

grizewald:

--- Quote from: tggzzz on August 09, 2022, 08:58:22 pm ---
--- Quote from: grizewald on August 09, 2022, 08:33:39 pm ---These particular cells were designed to withstand being transported in any orientation, given suitable packaging, so it's not really that surprising that it was still OK.

--- End quote ---

I haven't seen any info to that effect, but that is absence of evidence, not evidence of absence. Any refs?

--- End quote ---

In the attached document from Muirhead, they say: "The construction of the cell elements is such that, with suitable packing, they may be transported in any position."

I remember seeing your much older examples of the same cell. Are they still as stable as mine?

tggzzz:

--- Quote from: grizewald on August 10, 2022, 08:01:14 pm ---
--- Quote from: tggzzz on August 09, 2022, 08:58:22 pm ---
--- Quote from: grizewald on August 09, 2022, 08:33:39 pm ---These particular cells were designed to withstand being transported in any orientation, given suitable packaging, so it's not really that surprising that it was still OK.

--- End quote ---

I haven't seen any info to that effect, but that is absence of evidence, not evidence of absence. Any refs?

--- End quote ---

In the attached document from Muirhead, they say: "The construction of the cell elements is such that, with suitable packing, they may be transported in any position."

I remember seeing your much older examples of the same cell. Are they still as stable as mine?

--- End quote ---

Thanks for the PDF; saved.

I certainly haven't done any "formal" measurements of stability, but I have informally showed it is a good temperature sensor, e.g. https://www.eevblog.com/forum/metrology/weston-cells/msg4093978/#msg4093978 and https://www.eevblog.com/forum/testgear/muirhead-kvd-and-internal-corrosion-ignore-it-or-fix-it/msg2894446/#msg2894446

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