Evershed's Moving Coil Ammeter

(Substandard milliammeter)

Serial No.354944

Evershed's Moving coil ammeter moving coil instrument in wooden case, 0-500 milliamps DC. Evershed and Vignoles Ltd, UK, date unknown.

This is one of many instruments collected by Jack Davidson C Eng FIEE which I have been given by Dr Graham Winbolt

The S.S.on the meter scale plate indicates that this is a sub-standard instrument [see below]. On the underside of the case is a metal sleeve which houses and protects the instruction card shown here:

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.