Measuring resistance with a 1915 Leeds and Northrup Wheatstone Bridge

Christmas gift from my daughter, Jenni and son-in-law Mike. It’s a 1915-released Leeds and Northrup Type-S (model 5300) Wheatstone bridge-telephone/telegraph line testing set. It is designed to give very accurate measurement of resistance values, down to .001 ohm! The battery case was absolutely clean. I installed 3 “D” batteries and to my surprise, it functions perfectly with incredible accuracy. It is more accurate than my best digital meter. A look inside reveals the incredible quality of the internal switches. The precision resistors are coils of resistance wire wound in such a way as to cancel the coil inductance. I found the unit in an old 1920 Northern Electric catalog. It sold for 90.00 USD in 1920. That is equivalent to 2,742.00 in 2019 dollars!!

Resistance to test is placed between binding posts in lower right corner of panel. Resistance range is selected with upper left dial. Buttons under meter are pressed to connect battery to bridge and meter to bridge. If meter reads on + side, add resistance with thousands dual until meter swings to negative side. Do same with hundreds, tens, and ones dials until meter reads zero. Read resistance from dials and apply multiplier set by range switch. Sounds complicated, but can be done in seconds.

There are provisions for an external 5 vdc power source and external galvanometer.

Love the knife switches on left edge, used to configure unit for telephone loop tests. Can be used to locate distance to a crossed-wire or wire to ground fault. There are special range dial and knife switch combinations for the Murray Loop Test and Varley Loop Test. I have yet to research exactly what these are.

Mr. Northrup actually designed this model. It was made for decades, repackaged into a more modern case with much cheaper switch construction and wiring.

I'm hoping to find a manual and schematic, although the card in the lid has quite good instructions.

Been measuring things like the resistance of an unfolded paper clip! 🤓

[WCFL]

Thanks for this great demonstration! After seeing your video, I bought one for myself off Ebay. This is just what I've been needing to test a drawer full of extremely low ohm resistors quickly and reliably. The fact that this bridge can find faults on long lines, down to the foot is another great reason to own this. The lid instructions state how to use the bridge as a variable resistance sub box. Finally, the fact that it can be used with an external indicating device & and/or power supply make it handier yet.

[rustyrebar]

Nice.. I have a capacitanc bridge from that same era. You've inspired me to make a video about it.!

[theshannonlimit]

I have one of these from 1969. The most interesting part is how little changed in 54 years.

[Bodragon]

The needle at 5499 ohms is slightly to the right of center.
You are looking at the dial from the right which accounts for the error.
The camera is directly above, and needle is definitely to the right.
>

[PinnaclesPeak]

Thanks, helpful. Would the process be the same to measure the resistance of a motor winding?

[nationofgandhis]

Thank you had a buddy whose dad was vp there.... Any how got a model 7655 with EMF AND GA options. Not set up like yours at all. No Idea just starting to dig in on history

[electricalcontractor]

What is the battery voltage you are using
And what type