scope:

This specification covers the general requirements for servomotor-tachometer generators integrally built in the same housing utilizing the same shaft. It is not complete in itself, but must be used in conjunction with MIL-S-81963 which forms an inherent part of this specification. The servomotor section is a precision two-phase induction motor of low inertia. The generator section is a dual winding device in which the rotor accomplishes magnetic coupling, upon being rotated, between the input and output windings, producing an output proportional to speed and a polarity as a function of direction of rotation. The generator output frequency is identical to the energizing frequency.

The nomenclature consists of the item name, Servomotor-Tachometer Generator, followed by a type designation and a modification letter. All servomotor-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. The type designation should be preceded by the rated voltage of the motor reference winding followed by the letter "V" when the voltage is other than 115 volts. The complete nomenclature of a frame size 15, 115 volt (rated reference winding) servomotor-tachometer generator is illustrated in Table I. 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.

If the servomotor-tachometer generator illustrated in Table I was a unit whose servomotor required a rated input voltage of 26 volts, the nomenclature would become 26V-15SM-DG4A. This unit would be a size 15 servomotor-damping tachometer generator whose servomotor is normally excited with a rated voltage of 26 volts, 400 Hz and would also be the basic issue of the unit.

The first two digits designate the maximum diameter in tenths of an inch of the servomotor section of the servomotor-tachometer generator. If the diameter is not exactly a whole number of tenths, the next higher tenth is used.

The succeeding two groups of letters separated by a hyphen designates the function of the servomotor and the tachometer generator sections, respectively, in accordance with the following code:

First two-letter group Function SM Servomotor Second two-letter group Function DG Damping Tachometer Generator RG Rate Tachometer Generator IH Integrating Tachometer Generator, Heater Compensated IN Integrating Tachometer Generator, Network Compensated

The succeeding digit indicates the design frequency of the servomotor section of the servomotor-tachometer generator in accordance with the following code:

Frequency Code 60 6 400 4

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

The part identifying number (PIN) should consist 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 denoting the latest modification letter in the type designation, as shown in Table II.

A servomotor-tachometer generator is a unit consisting of a servomotor and a tachometer generator integrally coupled on a common shaft and enclosed in the same housing.

All standard servomotor-tachometer generators must be arranged to ensure that the normal mounting and pilot surfaces are contained on the servomotor section.

Ideal characteristics of all tachometer generators include low inertia rotors, high output-to-null ratios, a strictly linear relationship of output voltage as a function of rotor speed over a broad range of ambient temperatures, and a minimum phase shift between the fundamental output and input voltages. The maximum degree to which any one of the ideal characteristics is achieved is often at the expense of the remaining. General practice is to group tachometer generators in accordance with their anticipated application.

Tachometer generators in this group are characterized by high theoretical stall acceleration figures and low null output, and are employed to stabilize the parent system.

A rate tachometer generator is a generator characterized by a relatively high output-to-null ratio, and as such, is employed in high-gain rate and computing servomechanism applications. The rotor is of relatively low moment of inertia. Such applications require a high degree of linearity over the range of speeds of the generator.

An integrating tachometer generator is a generator used in computing applications requiring integration of a variable with respect to time. This type of tachometer generator is characterized by very small deviations of the output voltage as a function of temperature and a minimum warm-up time. Temperature control and compensation networks are usually integral parts of integrating generators.

intended Use:

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