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Description: | 15 AMP C 138474 ( maximum range of the instrument fitted with this coil and the instrument serial number) MANU The Record Electrical Company Limited. circa 1930 Broadheath, Altrincham, Cheshire, England DES after THOMSON,William,Lord,1st Baron Kelvin of Largs. circa 1885 Glasgow, Scotland. DES after FARADAY,Michael. 1831 The Royal Institution of Great Britai This is a coil for a Record Electrical ;"cirscale", "change-coil", moving iron ampere meter. Kelvin's moving iron meters were not very accurate due to hysteresis and inadequate damping of the movement. They also had none linear scales so their ranges were short.
The machine that this coil belongs to overcomes, to some extent, most of these problems. There is a large semicicular air damping cell enclosing a large vane attached to the pointer and there is also spring damping. The range is extended by having six interchangeable scales on a rotating drum each calibrated for a particular coil, The coils fit over the cylindrical aluminium casing that surrounds the galvanometer movement, which protrudes downward from the main casing. The problem of hysteresis (the creation of a dipole moment of a ferromagnetic substance in an electric field.) is partially solved by the shape of the moving vane of soft iron foil. The moving vane sits in a hemicylinder of soft iron foil that shields it from half of the field of the coil that surrounds it. The moving vane is also hemicylindrical so that as it moves the surface area of the vane exposed to the coil's field increases. Soft iron is used because it does not retain any magnetic properties that might be imparted by the Earth's magnetic field or those induced in the coils surrounding it.
The six copper coils vary in current capacity; this is coil C giving the instrument a range of 0 to 15 amp the others are, A which is 0-1 amp, B which is 0-5 amp, D which is 0-50 amp, E which is 0-180 amp and F which is 0-600 amp. | License: | http://www.hmag.gla.ac.uk/spirit/rights/ | Publisher: | Hunterian Museum and Art Gallery, University of Glasgow | Rights holder: | Hunterian Museum and Art Gallery, University of Glasgow | Subjects: | SCIENTIFIC COLLECTION : | Source: | Hunterian Museum | Creator: | Hunterian Museum and Art Gallery, University of Glasgow | Identifier: | http://www.huntsearch.gla.ac.uk/cgi-bin/... | Language: | en-GB | Go to resource |
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