Early electrical measurement

[gar]

170713-2332 EDT

The following link provides some background on early electrical measurement from the perspective of the Weston Electrical Instrument Co, 1888, in 1938.

http://archives.njit.edu/vhlib/weston-library/invisibles/weston-measuring-invisibles.pdf

By 1870 electrical resistance could be measured with reasonable accuracy by the Wheatstone bridge.
https://en.wikipedia.org/wiki/Wheatstone_bridge

But there was no very accurate and stable means to measure current or voltage. Nor were available voltage references very stable.

A tangent galvanometer was unstable as an indicating instrument because of the varying magnetic field. As a null indicator it could provide accurate resistance measurements as the null indicator in a Wheatstone bridge.

d'Arsonval developed an indicating instrument, but its magnetic field intensity degraded with time, 1882. https://en.wikipedia.org/wiki/Galvanometer

Weston developed means to obtain a long term stable magnetic field, and it was moderately shielded from external magnetic fields.

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[junkhound]

Back in the 70's spectrum had a article titled, IIRC, "Volta as voltmeter", describing Volta's 'pain' descriptions, etc.

Whoops, looked it up, thought that article was longer ago than 1993.

http://ieeexplore.ieee.org/stamp/stamp.jsp?arnumber=7891777

 

[gar]

170714-1026 EDT

junkhound:

I haven't gone directly to the article yet.


One can not make a useful coil of copper or other conductive wire without the wire being insulated. In searches about galvanometers the resulting discussions don't talk about this critical factor. See http://www.tandfonline.com/doi/abs/10.1080/00033790110117476 .

In my early days of playing with electrical circuits hookup wire was cotton covered. Note: you can probably get a much thinner insulation layer with silk than cotton.

Enameled magnet wire was invented by https://en.wikipedia.org/wiki/George_Jacobs_(inventor) in 1907-1911.

Although not mentioned in the Weston discussion I have to assume silk insulated wire was used in the early instruments.

How many of you have ever done an experiment with a coil of wire and a compass to estimate the intensity of the earth's magnetic field at your location? This was a home work experiment I did for my junior college physics class. In recent years I had my granddaughter make the coil and run the experiment.

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