scope:

This specification covers the general requirements for tachometer generators. It is not complete in itself, but should be used in conjunction with MIL-S-81963 which will form an inherent part of this specification.

The nomenclature consists of the item name, Tachometer Generator, followed by a type designation and an uppercase modification letter. All tachometer generators having the same nomenclature should be electrically and mechanically interchangeable for all military applications. The type designation is made up of a combination of digits and letters as explained in the following paragraphs. Types other than 115 volts should be prefixed by applicable voltage identification followed by the letter "V" such as "26V". The type designation of a 15IH4A is illustrated in Table I. Nomenclature for new or modified tachometer generator types will be assigned by the Naval Air Systems Command, Department of the Navy.

The first two digits designate the maximum diameter in tenths of an inch. If the diameter is not exactly a whole number of tenths, the next higher tenth is used. Beneficial comments (recommendations:, additions, deletions) and any pertinent data which may be of use in improving this document should be addressed to: Systems Engineering and Standardization Department (Code 53), Naval Air Engineering Center, Lakehurst, NJ 08733-5100, by using the self-addressed Standardization Document Improvement Proposal (DD Form 1426) appearing at the end of this document or by letter.

The succeeding letter group indicates one of the following functions:

RG Rats tachometer generator IH Integrating tachometer generator, heater compensated IN Integrating tachometer generator, network compensated DG Damping tachometer generator

The succeeding digit(s) identifies the frequency of the power supply in accordance with the following code:

Supply frequency (Hz) Code 60 6 400 4

New codes associated with supply frequencies not indicated will be assigned as required by the Naval Air Systems Command, Department of the Navy.

An upper case letter "A" following the frequency digit indicates the basic issue of a standard tachometer generator. The first modification that significantly affects the external dimensions or the electrical characteristics of the basic type should be indicated by the upper case letter "B". Succeeding modifications will be indicated by "C", "D", etc., except the use of letters "I", "L", "O", and "Q" is prohibited.

A tachometer generator classified as a 15IH4A (see Table I) indicates the original design of a 115 volt, 400 Hz, heater-compensated, integrating tachometer generator whose body is greater than 1.40 inches but not greater than 1.50 inches. If the unit had an input voltage requirement of 26 volts, the type designation would be 26V-15IH4A.

The part identifying number (PIN) consists of the letter "M", the basic number of the specification sheet (not including the revision letter), an assigned dash number, and an upper case suffix letter designating the latest modification letter in the type designation, as shown in Table II.

intended Use:

The intended use for tachometer generators covered by this specification must be in accordance with MIL-S-81963.