Evershed and Vignoles Time line

How old is my meter? what is it?

People regularly contact me asking how old their newly acquired vintage instrument might be. This often proves very difficult since Evershed and Vignoles used the same method of construction for their instruments over many years. I have tried to establish whether it might be possible to estimate the date of manufacture from the serial numbers. I have looked at information given to me by contributors and searched the internet and examined the entries on auction sites. From what I have been able to glean it would seem that the serial numbers start from a low number and increase over the years. There does not appear to be any kind of date code included in the numbers, though it seems likely that blocks of serial numbers were allocated for instruments of a particular type.

I have so far found 35 instruments and pieces of equipment [not exclusively meggers] where serial numbers have been given or are visible on photos. The earliest, an ammeter dated 1895 has a serial number 1,656 and the latest, a megger has a serial number 2,606,230. By correlating the numbers with the dates for the various patents etc. I have produced this very rough guide to those manufactured at the Acton works from 1903:

    9 000 after 1903
   48 000 after1910
   96 000 after 1919
  147 000 after 1926
  170 000 after 1928
  260 000 after 1935
  320 000 after 1940
  430 000 after 1942
  788 000 after 1945
  800 000 after 1950
1 000 000 after 1954
1 500 000 after 1963
2 000 000 after 1968

The origins of the firm begin in 1886 and although it lives on under the MEGGER label it ceased manufacturing at the works at Acton Lane in 1986. The following is a time line history of the firm which I trust will help date instruments made by the firm prior to the takeover by AVO International in 1986. It would seem that there were periods when the firm was making instruments to both the new and the old designs. They also manufactured instruments based upon a principle patented a year later.

1881 Professors Ayrton and Perry invent the voltmeter and ammeter [they also coined the words]
1882 Ayrton invents the first true ohmmeter with moving magnet and two coils
1885 Evershed makes his first moving iron voltmeter
1886 Evershed working for Goolden and Trotter in Westminster, London
1886 Soft iron armature voltmeters and Cardew hot wire ammeters switchboard instruments
1888 Weston USA produced the first moving coil instrument
1889 Goolden and Trotter started making a two part ohmmeter with magneto and separate meter
1889 Ayrton and Perry's ohmmeter and hand generator patented
1890 The single needle design replaced with two magnetised in opposite directions
1890 New generator design gives smoother output
1888 Manufacture started in Westbourne Park, London
1895 Evershed and Vignoles started at Woodfield Works, Harrow Road, London
1899 E&V started making moving coil meters
1899 Generator improved again, transformer stampings roller bearings rotating disc commutator and patented, this design to become the '1900 pattern' testing set
1903 Move to new factory in Acton Lane Chiswick, London
1903 The word MEGGER registered as a trade mark
1903 Meter with moving coils and centrifugal clutch incorporated for first time
1904 The meter and generator are housed in one box 'Megger testing set' with or without slipping clutch.
1905 'Bridge megger testing set', insulation, Wheatstone bridge and cable fault detection in one box [200MΩ to 0.01Ω]
1909 set up agents in other countries including USA
1909 Murday pen recorder unique rectangular scale
1910 Biddle in USA start making Meggers
1910? DIONIC water conductivity tester 4mA at 100 V
1910 DUCTOR low resistance tester 15A at 1V [typical] power supplied from battery
1922 lighter model in aluminium casing 'MEG insulation testing set' 0-100 Mohm introduced later to be called the series 2 which remained in production until 1963
1922 The inventor of what was to become the AVOmeter approached the company with a view to manufacture. The offer was rejected by Sydney Evershed
1926? Earth testers in both the 'megger' and 'meg' range available
1929 'Bridge Meg' introduced [metal casing]
1930 Improvements to meter pole pieces to linearise the scale
1931 'Megger' and 'meg' earth testers
1931 Midworth control system
1932 'WEE' megger introduced [Bakelite case] made in response to a smaller prototype made by GEC
1941 'WEE' megger updated RC components added
1946 Safety ohmmeter introduced
1947 'Noflote' level control system
1950 The whole range of ohmmeters redesigned to be more sensitive reclassified as 'Series 1' (0-2000 Mohm)'series 2'(0-100 Mohm and 'series 3'
1950 Series 4 introduced
1951 instruments start appearing with a new logo EVERSHED surrounded by a parallelogram
1955 E&V acquire Record Electrical Co Ltd a firm started in 1911 by JW Record
1960 Series 3 Mk 3 with AC generator and diode rectifier introduced, insulation and continuity tester, nylon gear wheel.
1960 E&V producing 32 instrument variations 
1961 E&V taken over by BAT, rationalisation introduced
1961?  Instruments start appearing with a new logo MEGGER surrounded by a parallelogram
1962 Transistorised continuity and insulation tester introduced. This used a milliammeter movement rather than the crossed coil movements of the hand cranked versions
1963 Line earth loop tester introduced for testing of installations for compliance with IEE wiring regulations
1963 Major Megger replaces the series 2, available in 4 versions
1963 AC generators with diode rectifier or doublers instead of the DC type used since the 1880s
1965 BAT sold E&V to George Kent
1967? Kent and Cambridge Instruments merge
!967 Thorn take over of Metal industries which owned AVO Ltd
1968 AVO acquires Evershed and Vignoles manufacture continues at Megger Instruments Division of E&V Ltd (instruments also being made in Dover)
1971 Parts of E&V disposed of to Metal Industries (part of the Thorn Group)
1982 Part of Thorn EMI Instruments Ltd together with AVO and HW Sullivan
1983 E&V owned by BestoBell (then Meggitt in 1986) until 1990
1986 Chiswick factory closes
1991 Name change AVO Megger instruments Ltd
2000 Name change AVO international Holdings
2002 Name change AVO International Ltd
2002 Name change Megger Group Ltd

I would welcome corrections or updates to the above note that the figures given are typical values, instruments were made for a wide range of applications.

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