Author Topic: #1000: My (hi)story of the Weston cell, of the Volt, and of being a volt-nuts  (Read 17788 times)

0 Members and 1 Guest are viewing this topic.

Offline HighVoltage

  • Super Contributor
  • ***
  • Posts: 4252
  • Country: de
That is impressive with a cell from '43
Some of these cells are just amazing, how long they stay stable.

What is the input impedance of the advantest DMM in the mV range?
Also interesting that the advantest shows above 1000 mV in the mV range.
There are 3 kinds of people in this world, those who can count and those who can not.
 

Online beanflying

  • Super Contributor
  • ***
  • Posts: 3706
  • Country: au
  • Toys so very many Toys.
It is a 2 million count meter and 10^10+ Ohms on the lower ranges as standard. The cells were removed from a local Uni Physics Lab (RMIT Melbourne) in 1975 and haven't been used since.

Just a cool thing to add to the collection and I am rolling an 3DP/Laser Enclosure to have a clear Perspex side for the un cased Tinsley one for display.
Coffee, Food, R/C and electronics nerd in no particular order :)
 

Offline tggzzz

  • Super Contributor
  • ***
  • Posts: 9885
  • Country: gb
    • Having fun doing more, with less
That is impressive with a cell from '43
Some of these cells are just amazing, how long they stay stable.

I have 1949 cell that is similarly in spec.

Saturated cells last but have a 40uV/C tempco around 20C. Unsaturated cells have a lower tempco, but don't last anywhere as well.

Here's some information from the NBS ("The construction and characteristics of standard cells" http://digicoll.manoa.hawaii.edu/techreports/PDF/NBS84.pdf ):



There are lies, damned lies, statistics - and ADC/DAC specs.
Glider pilot's aphorism: "there is no substitute for span". Retort: "There is a substitute: skill+imagination. But you can buy span".
Having fun doing more, with less
 

Online beanflying

  • Super Contributor
  • ***
  • Posts: 3706
  • Country: au
  • Toys so very many Toys.
Just because it is a little different I cracked the case on the Cambridge Cell to see what made it not tick.

While it is a single tube outer it appears to have a second inner glass with the base of it containing liquid Mercury and then into what looks like some sort of flock barrier and back outside the inner tube to the Amalgam.

$0.02 Teardown and also so it doesn't get lost in TEA

Coffee, Food, R/C and electronics nerd in no particular order :)
 

Offline ArthurDent

  • Frequent Contributor
  • **
  • Posts: 869
  • Country: us
Some may find this interesting.

The story of standard cells has some footnotes. Eppley tried what they thought was a innovation in cell enclosures and temperature control with their model 119 three cell enclosure. Instead of being heated, it used peltier effect coolers to maintain the temperature just a few degrees above zero degrees C. The theory was that, if you look at a graph of the voltage vs temperature of a cell, rather than heat the cells up, the enclosure cools the cells to the turning point in the temperature curve where the change is basically a flat line, or zero. What they apparently found, from what I heard, was that there were condensation problems and the idea was scrapped. I don’t know how many of these units were made but there is at least one which I own.

Attached is a temperature curve showing the zero point and a photo of the outside front of the 119 enclosure that has two heatsink enclosures with the power supply and peltier effect controllers on each side plus a large heatsink on the back of the center unit. The inside has a beer can size cylinder holding the 3 cells surrounded by rigid foam. There is a thermometer well hole in the middle and a matching hole in the cover plate. 
 
The following users thanked this post: TiN, Andreas, HighVoltage, razvan784, grizewald

Offline ArthurDent

  • Frequent Contributor
  • **
  • Posts: 869
  • Country: us
Here are some photos of a more conventional standard cell enclosure/oven, my Guildline 9152-R4. You can see that the leads from the cells (inside the clear tubing) goes around each of the three concentric housings one complete turn to prevent heat creep on the leads. The leads are small and you’d think they would want to keep them as short as possible to minimize drops, but when measured using a bucking voltage to balance the cell voltage, you are drawing no current so there is no voltage drop on the leads. 
 
The following users thanked this post: Dr. Frank

Offline ArthurDent

  • Frequent Contributor
  • **
  • Posts: 869
  • Country: us
Here is a photo of a dead Muirhead saturated cell. although it doesn't say, I'm pretty sure it is a saturated cell.  8)
« Last Edit: May 10, 2019, 05:42:03 pm by ArthurDent »
 

Online beanflying

  • Super Contributor
  • ***
  • Posts: 3706
  • Country: au
  • Toys so very many Toys.
Interesting info on the cold option.

There is a couple of Heated Cabinets on evilbay for more than I would consider so I will make do. The curio factor and stability over decades is still fascinating.

I still have no real plans for my lot and if more come up for not much I may add to the fleet just because they are a cool toy  :)

Coffee, Food, R/C and electronics nerd in no particular order :)
 

Offline ArthurDent

  • Frequent Contributor
  • **
  • Posts: 869
  • Country: us
The problem with buying a standard cell enclosure now is you never know the condition of the cells inside. When I bought my Guildline 9152-R4 a few decades ago, the seller said one of the cells was iffy and the voltage on that cell is a little low. I just remeasured the internal resistance of all four cells and 1, 2, and 3 are between 900 and 1000 ohms, which is near the high end of acceptable, but the 4th one reads almost 4000 ohms.

The way the internal resistance is measured is indirectly by checking voltage drop with a known load resistor. Although some references say use a 1 megohm resistor, a 10 megohm resistor is better. I use my HP735A as a bucking reference for the cell under test and an HP419A as the difference indicator. I also monitor the HP735A voltage with an HP3457A for a double check. You can use this formula to calculate cell internal resistance. 
 

Offline schmitt trigger

  • Super Contributor
  • ***
  • Posts: 1331
  • Country: mx
Subscribing to a fascinating thread.

I have visited Newport, RI previously. Surprising that a quaint resort town better known for its ultra-wealthy mansions and Jazz festivals, is also home to Eppley Labs.
 


Share me

Digg  Facebook  SlashDot  Delicious  Technorati  Twitter  Google  Yahoo
Smf