3 ms·
The Weston Standard Cell (2011)
- mzs 6y agomore info including photos and how they were used to accurately measure voltages: https://entertaininghacks.wordpress.com/2016/12/28/a-weston-standard-cell-an-introduction-to-voltnuttery/ https://entertaininghacks.wordpress.com/2016/12/28/a-weston-...
- analog31 6y agoI've got one. It's in an ancient Leeds and Northrup potentiometer that was made for reading a thermocouple. You use the cell in two stages. First, you adjust a conventional variable voltage source until it equals the Weston cell. Then you leave the Weston cell alone and use the variable source for subsequent input voltage measurements. That way, you maximize the lifetime of the Weston cell. As for the potentiometer, it's a precise resistive voltage divider. You dial a voltage until it equals the input voltage, then read the position of the dial on a scale. That's your measurement. This application is also where "potentiometer" gets its name. The indicator for when two voltages are equal, is a super sensitive galvanometer. You push a button to make a measurement, seeing if the needle moves to the left or right. So the Weston cell is actually only doing anything for a split second. The whole thing contains no active electronics. All I've done with it is to make one thermocouple measurement, and to very briefly test the cell with my digital voltmeter.
- opwieurposiu 6y agoThe switches and knobs on that old testgear are so satisfying to use. Clunk Clunk, POP!. I have a Leeds and Northrup bridge and some decade resistors and they are still 0.01% accurate after 80 years!
- analog31 6y agoI love the mahogany boxes too. Sadly, mine is newer and has a painted steel box. I'm thinking of replacing the Weston cell with a solid state voltage reference so I can dispose of the cell but keep the instrument.