Electronics > Metrology

L&N 4393 Universal Ratio Set

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Vgkid:
Leeds and Northrup 4393 Universal Ratio Set
Background, since it is in the mail:
What is a Universal Ratio Set?
A Universal Ratio Set or URS(abbreviated) is best thought of a a slide wire. A 3 terminal restive voltage divider. One that has a constant input resistance, and a varying output resistance(simplified).
A more descriptive version is to imagine 2 resistor decade boxes connected together, except the switches are wired in a way so that as one turns one way, the other turns the opposite way. As the resistance is increased in the first decade, the total resistance decreases in the second. A 20 step 100 Ohm decade connects the two decades.

Now there some upgrades since this basic version was created, as shown below.

Here are the specs for the newest variant, note the number of extra binding posts, and additional switches. I will go into detail later. For this version, that is almost $19.1K today. And you thought that that the 3458A was expensive, when It comes to L&N factory prices they can only go up...
Expect a massive info dump, until I get my unit.

Vgkid:
For those wanting to read ahead look into these:
A Versatile Ratio Instrument for the High Ratio Comparison of Voltage or Resistance
nvlpubs.nist.gov/nistpubs/jres/70C/jresv70Cn3p169_A1b.pdf
Practical Methods For Calibration of Potentiometers
https://archive.org/details/practicalmethods172rama
Precision Measurement and Calibration Selected NBS Papers on Electricity — Low Frequency
nvlpubs.nist.gov/nistpubs/Legacy/SP/nbsspecialpublication300v3.pdf
^^*A must read*^^

Vgkid:
Well it came, the info dump will be explained as I go.

With this, we can see that the number of binding posts doesn't match up with the more modern unit that is in the advertisement. One thing that is similar, is the weight. This thing has to easily be the densest piece of equipment that I own. The shipping weight to me was 43 pounds, with about 3 pounds of it being cardboard, It was packaged very well.

Popping off the cover we are greeted with a insulated box, and another black Bakelite box holding all of the goodies. The insulation used is a thick layer of cork, I was fearing a fibrous type of insulation. The Bakelite box is lined with copper sheeting.
Spoiler ye olde voltnut voodoo

 I haven't had a chance to tear it down properly yet, so I will add some better pics tomorrow..

lowimpedance:
I do like looking at the way construction was done in the days past by different companies, have not seen cork used before in other gear of this vintage.
Rather interesting plastic resistor carrier around the switch.
Thanks for the pics.

Vgkid:
It is interestinv how different companies assembly there gear. L&N seems to like these specialty fasteners which do not require a tapped hole to fasten into, just a lip on 2 sides. They are a pain to get lined up to remove. The cork as an insulator is neat.
Just wait until I start posting the teardown pics. >:D   8)

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