scope:

This Standard specifies the performance requirements for sealed, flush mounting, ammeters, voltmeters, wattmeters, and frequency indicators and is generally in agreement with British Standard 89: 1977(IEC 51). The instruments have a nominal barrel diameter of 50 mm, 65 mm, 90 mm, and 100 mm. For the purpose of this specification a sealed instrument has a defined maximum leakage rate (see clause.A.21).

In accordance with international practice the Class Index system adopted in BS 89: 1977(IEC 51) is used in this specification. Reference should be made to BS 89: 1977(IEC 51), particularly the Foreward and Appendices for more precise information on this system. For specific information concerning the particular class indices adopted, see Table A on page 10 of this Defence Standard.

Defence Standard 66-7(PART 2), gives preferred ranges for ammeters, and voltmeters. Further PARTS to this Defence Standard will be added to extend the scope to include frequency indicators, wattmeters, and power factor indicators.

When it is desired to use a range of instruments or to indicate by electrical means quantities not specifically covered by the instruments listed in the associated Defence Standard 66-7(PART 2), or the relevant PART of this Standard, a manufacturer or a design authority may request that such items be considered for inclusion in this document. In such instances, details of dial markings and any special requirements together with the appropriate drawings, shall be submitted to the Qualification Approval Authority.