MIL-PRF-19E
(Copies of this document are available from https://www.ncsli.org/ or from the National Conference of Standards
Laboratories (NCSL) International, 1800 30th Street, Suite 305, Boulder, CO 80301-1026.)
2.4 Order of precedence. In the event of a conflict between the text of this document and the references cited
herein (except for related specification sheets), the text of this document takes precedence. Nothing in this
document, however, supersedes applicable laws and regulations unless a specific exemption has been obtained.
3. REQUIREMENTS
3.1 Associated specifications. The individual part requirements shall be as specified herein and in accordance with
the applicable associated specification. In the event of any conflict between requirements of this specification and the
associated specification, the latter shall govern (see 6.2).
3.2 Qualification. Resistors furnished under this specification shall be products which are authorized by the
qualifying activity for listing on the qualified products list (QPL) before contract award (see 4.4 and 6.3).
3.3 Material. Materials shall be used which will enable the resistors to meet the performance requirements of this
specification. Acceptance or approval of any constituent material shall not be construed as a guaranty of the
acceptance of the finished product.
3.3.1 Ferrous metals. Unless specifically approved by the government, the use of ferrous material, with the
exception of corrosion resistant steel in the resistance element, is prohibited.
3.3.2 Pure tin. The use of pure tin, as an underplate or final finish is prohibited both internally and externally. Tin
content of resistor components and solder shall not exceed 97 percent, by mass. Tin shall be alloyed with a minimum
of 3 percent lead, by mass (see 6.8).
3.4 Interface and physical dimensions. The resistors shall meet the interface and physical dimensions specified
(see 3.1).
3.4.1 Windings. The resistance element shall consist of a winding of resistance wire or ribbon, on a form, which
shall not char or break down at any combination of temperatures and loads specified herein. The element shall be
wound in a manner to conform with the specified taper. Joints, welds, and bonds shall be held to an absolute
minimum.
3.4.2 Resistance wire. The resistance wire used shall possess a substantially uniform cross section of conductor.
The wire shall be as free as practicable from particles of impurity and grain growth or other factors contributing to stop
weakness, In no case shall the wire diameter or ribbon thickness be less than 0.00175 inch (0.0445mm) nominal
before winding or less than 0.00156 inch (0.0396mm) absolute minimum after winding.
3.4.3 Operating shafts. Operating shafts shall be made of corrosion resistant metal or metal which has been
plated for corrosion resistance, and shall be electrically insulated from current carrying parts. The slot portion,
diameter, and length of the operating shaft shall be as specified (see 3.1). In all cases, operating shafts shall be of
such length that the slot depth will not interfere with shaft retainers.
3.4.4 Rotation. The total mechanical rotation and electrical rotation shall be defined on figure 1, and as specified
(see 3.1). The theoretical electrical rotation of resistors with switches shall be equal to the rotation from the stops at
the end opposite the switch to the point where the members just engage to actuate the switch to the "off" position.
3.4.4.1 Clockwise taper. A clockwise taper is resistance taper in which the resistance varies approximately as
shown on figure 2, increasing as the rotation angle increases in a clockwise direction as viewed from the operating
shaft, and measured between the left terminal and the rotating contact terminal, indicated as 1 and 2, respectively, on
figure 1.
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