[volt-nuts] Ayrton Shunt does double duty.

geoelectronics at rallstech.net geoelectronics at rallstech.net
Fri May 4 09:55:14 EDT 2018

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

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