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

[trobbins]

A chance to test a Weston cell recently was thwarted by the Fluke 801BR I was restoring being the /AG version with a zener.  But I now have two cells to ponder over - a Tinsley Normal that I understand is a saturated version with crystals visible, and an Australian made version made by Munitions Supply Labs (MSL operated from 1922 to 1948) that I can't easily identify if it is saturated or not.

The Tinsley measures 1.0124V at 19C with a Keithley 197 (>10G rated, and about 1nA of measured bias with a 10Meg load), so may have had a hard life given it came from a technical college, and had a nameplate 1.0183V value at 20C.  Post #28 from HighVoltage in 2016 indicates that some oven heating may be worthwhile, so I will try that in a few weeks if there has been no change.  Btw, HighVoltage you commented that one of your cells degraded badly earlier this year - was that cell the same as the cell you recovered by heating back in 2016?

The MSL measures 1.0187V and so may be nominally ok, and has a makers label with 1.0184V at 20C.  Given this unit is circa 79 years old, that suggests it is a saturated version although the base portion of the cell glass is coated in black so I can't confirm.

[HighVoltage]

Post #28 from HighVoltage in 2016 indicates that some oven heating may be worthwhile, so I will try that in a few weeks if there has been no change. 

Btw, HighVoltage you commented that one of your cells degraded badly earlier this year - was that cell the same as the cell you recovered by heating back in 2016?

Yes, this was the cell that arrived badly, was revived and stayed stable for some time but now I would consider it dead.

All my other cells are still well.

[trobbins]

Ta, that seems to be a typical outcome from any rejuvenation attempt on a grossly discharged wet battery cell.  Do you recall where the 60C heating scheme came from, or was commented on?

A 1907 paper from the Royal Society adds some context to the historical development of the saturated Weston cell https://royalsocietypublishing.org/doi/pdf/10.1098/rsta.1908.0010

[HighVoltage]

I had one old documentation that mentioned this oven re-conditioning. I would have to look, to find it again.
The problem is probably also, that we have no idea what has happened to these cells over so many years. Many have most likely been handled by people who do not even know what this is.

However, I find it impressive that some old cells are still so stable after 50+ years.

[eppley]

Just FYI. The Standard cell division of Eppley Labs in Newport RI was shutdown around 2000 and the contents were donated to the Vintage Communications Museum in Windsor CT. The material and instruments sat in storage for about 20 years and are just now being organized and planning is underway to make a significant museum display from all of it. All the Eppley documentation is in the collection. There is data on every cell produced by eppley going back to the 1920's.  If someone needs original cell manufacture data (date of manufacture, final voltage, chemistry ......., please email me.

[eppley]

Sorry, I am a newbe here. Please send a message, not an email.

[edpalmer42]

Back in 2009 I contacted the Vintage Communications Museum and was able to get copies of the original data for two of my Eppley 100 cells.  Unfortunately, they couldn't find records for 3 bare cells.  I've attached a copy of the info that they sent so you can see what's included.

Ed

[trobbins]

WRT the 1961 factory record, would 40C be part of a forming or initial preparation process?

[eppley]

Material is a bit more organized now. If you want to forward the 3 bare cell serial numbers, I will take a more detailed look for the history. I will also look a bit further into the tests done at 40C. That may be specific to a very small group of cells. Testing at that temperature is not typical per the records.

[Conrad Hoffman]

FWIW, I had a Julie standard cell oven with Eppley cells. Julie was odd in that they used a higher temperature for the inner oven, 37C. Maybe higher temperature testing was for people like that.

[iMo]

I made a measurement (1 day long 34401A, HiZ input) on my Muirhead Ref Cell and got TC between +6..+9uV/C.
Is that typical for my cell (unsaturated perhaps)? It seems to me the TC is much lower, there is another mechanism influencing it (discharging in the HiZ DMM input?).
My cell is close to EOL based on the voltage, also I tilted it flat for a while before the measurement (grhh), anyhow below the data.
Muirhead D-845-D
Reference Cell
No: 459872

PS: added the graphs with first 3.5h cut off..

[Dr. Frank]

I made a measurement (1 day long 34401A, HiZ input) on my Muirhead Ref Cell and got TC between +6..+9uV/C.
Is that typical for my cell (unsaturated perhaps)? It seems to me the TC is much lower, there is another mechanism influencing it (discharging in the HiZ DMM input?).
My cell is close to EOL based on the voltage, also I tilted it flat for a while before the measurement (grhh), anyhow below the data.
Muirhead D-845-D
Reference Cell
No: 459872

PS: added the graphs with first 3.5h cut off..

Hello,
the 845-D is an unsaturated type, i.e. lesser T.C. (than the -40.6 µV/K of saturated ones), but higher annual drift.
If you search the Internet for "muirhead standard cell 845", you'll find a datasheet on eevblog, which specifies these types to have +/- 5µV/K.

So it's about the ballpark, what you measured, but you have to take the age (does T.C. increase, when a cell is really too old?), and your measurement method into consideration. Latter might show more hysteresis, than the real, lower T.C.. That's hard to decide from your measurements.
Have you properly ruled out the T.C. of your 34401A?

Frank

PS: I think the link to saturated / unsaturated types are here:
https://www.eevblog.com/forum/metrology/weston-cells/msg4031467/#msg4031467

[iMo]

Hi Frank, the TC of my 34401A is aprox +0.5ppm/C at 10V range, in the above graphs you may see raw data.
Moreover, I do not know my TC at the 1V range, I never did the measurement of my TC at 1V range..
Let us assume the TC is the same at 1V range  - see below the corrected TC (and with some light median filtering).

[trobbins]

Further to posts #79 and #83 by eppley, I contacted the museum and Barry M responded with some history, advice and photos of the relevant Eppley factory records for a 'MIN 1' model standard cell that is in an RFL model 829G AC/DC Calibration Standard I am part way through restoring.

The Eppley records confirm the calibrator was manufactured circa late 1974 to early 1975, which is also confirmed by datecodes on some internal parts.  One could suggest from those records that the batch of 25 cells ordered by RFL were for a nominal month of calibrator production, and further suggest that about 500 calibrators per annum were being produced, as the cell was an optional extra.  That sort of aligns with serial number information in the 829G manual, so a customer like RFL could well account for circa 1500 cells for a product line over 5 years.

The museum's donation of Eppley records involves about 20 shelves of three-ring binders and covers about a million cells, so that makes RFL just a minor user, given that Barry indicated they made circa 20-30 cells per day (eg. 6,500 per annum ballpark).

The cell in the calibrator is still functional at about 1.01811V, indicating a nominal 24uV loss per year, which is consistent with the 20-40uV/yr advice in NBL Monograph 84 from 1965, and is not behaving erratically so far.  The cell can stay in the calibrator, which luckily includes terminals for an external reference, and enjoy its retirement now that it has a copy of its birth certificate.

[Nanitamuscen]

Here is such a normal element that came into my hands as part of a large two-circuit thermostat. Surprisingly, he survived the delivery of the shipping company, most likely thanks to a thermostat weighing 20 kg.
Labels on top:
normal element
Grade 1 T 20 degrees Celsius
manufacturer 3-D
The Teplokontrol plant in Lviv
Assembly in 1956.
The inscription on the side: "Initial" "Exemplary"