Evershed and Vignoles Ammeter

(sub standard)

Serial No.685194

Evershed and Vignoles Ammeter Moving iron instrument in wooden case with carrying strap. Scaled 0-.25A and 0-.5A AC/DC selectable via terminals on top of the case. Evershed and Vignoles Ltd, UK, date unknown, though clearly before the handwritten label dated June 1948

This gift is one of a pair of instruments which Bill Hughes was given. They were originally owned by the Research Department of Evershed and Vignoles. The S.S.on the meter scale plate indicates that this is a sub standard (precision) instrument.

The following is an extract from a Company publication of 1932:

MR. EVERSHED'S original moving iron instrument made in the year 1885 was followed by a number of other instruments, and the Company now make moving iron, moving coil and dynamometer switchboard and portable instruments in a number of patterns.

The principle of the original Evershed moving iron instrument is still used by the Company, and has been adopted by at least one of their prominent foreign competitors.

The instruments are built, when required, to sub-standard accuracy, the maximum error allowed in this type being 0.2 of 1 per cent. Sub-standard instruments are specially suitable for research and laboratory work, and for the standardisation of industrial indicating instruments or watt hour meters. They are calibrated against standards frequently checked by the National Physical Laboratory, and are fitted with knife-edge pointers and anti-parallax mirrors to facilitate accurate reading.

In 1908, Eversheds originated the use of spring mounting for the jewels of their instrument movements to take the place of the solid mounting generally used at that time.

C M Deavin for copies of original Evershed and Vignoles documentation provided by Marion Heard, the publicity assistant at Megger back in 2003.