https://nvlpubs.nist.gov/nistpubs/Legacy/SP/nbsspecialpublication300v3.pdf has a few articles on potentiometers and volt boxes. F.K. Harris's Electrical measurements (1952) has further information.
Bruce > On 05 May 2018 at 09:36 Bruce Griffiths <[email protected]> wrote: > > > The volt box is likely to be a voltage divider that was used to divide a > voltage to be measured down to a value within the measurement range of a L & > N potentiometer (not the 3 terminal component but the type that sets up the > current in a series string of resistors to a known vale by comparing the > voltage across a subset with the voltage of a standard cell. The unknown > voltage can then be measured by comparing it against the voltage drop across > a adjustable subset of the series resistor string). > They are mentioned in various NBS (NIST) publications of the era as well as > in various texts on dc electrical measurements. They were in common use up > till around the 1980's. > > Bruce > > On 05 May 2018 at 01:55 [email protected] wrote: > > > > > > Hello Dave. > > > > So far I have identified 3 different Leeds & Northrup "Boxes". > > Originally my intention was to re-purpose the box, panel connectors and > > switch for a project to make my own precision resistor banks. > > > > All use different switches and vastly different resistors to achieve > > their original purpose. > > > > The subject of the first one is the "Ayrton (wired) Shunt Box". It was > > used with a galvanometer as a sort of attenuator (current divider), > > uniquely wired in the Ayrton fashion to insure the galvanometer was > > always connected to a shunt resistor, even during switching. Think of > > the scheme as a stepped potentiometer, the meter was between the two > > extremes, while the source went to the wiper. Just backwards from a > > Voltage divider. > > > > Next is the "Shunt Box". It's resistors are copper straps, the lowest > > value is made from a copper sheet maybe 5 inches wide, bent into a > > corrugated shape to fit inside the box. Remarkable construction, should > > be quite stable as a milliOhm standard. > > > > The last one is called "Volt Box". Its resistors are wire wound on > > ceramic forms, obviously with great care. The switch is protected and > > possibly gold plated contacts. Multiple series connected resistors are > > used to provide the correct values plus spread the current (heat load) > > around, and they are spaced far apart and with air space around each > > one. So far no clue as to its original function but of course I have > > traced the schematic. > > > > Very little is freely available on the 'net about them nor a period > > catalog so far. > > > > George Dowell > > _______________________________________________ > > volt-nuts mailing list -- [email protected] > > To unsubscribe, go to > > https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts > > and follow the instructions there. > _______________________________________________ > volt-nuts mailing list -- [email protected] > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts > and follow the instructions there. _______________________________________________ volt-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts and follow the instructions there.
