MIL-PRF-27208 Resistor, Variable, Wirewound, Nonprecision General Specification ForThis specification covers the general requirements for multiturn, lead-screw actuated and single turn wirewound, variable resistors with a contact bearing uniformly over the entire surface of the entire resistive element, wound linearly, when positioned by an actuator. These resistors are capable of full load operation \(where maximum resistance is engaged\) at maximum ambient temperature of 85 Degrees C, and are capable for continuous operation when properly derated, at a maximum temperature of 150 Degrees C \(see figure 2\). These resistors have a resistance tolerance of ┬▒5 percent \(see 3.1\).

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MIL-PRF-27208F

TABLE I. Resistance temperature characteristic.

Maximum resistance

Parts per million per oC

Symbol

temperature characteristic in

(ppm/oC)

percent/oC 1/

�0.005

�50

1/ Referred to an ambient temperature of 25 C.

1.2.1.3 Temperature characteristic. The temperature characteristic is identified by a single digit number in

accordance with table II.

TABLE II. Temperature characteristic.

Maximum resistance

Parts per million per oC

temperature characteristic in

Symbol

(ppm/ C)

percent/ C

85oC

150oC

1.2.1.4 Terminals. The terminals are identified by a single letter in accordance with table III.

TABLE III. Terminals.

Symbol

Type of terminal

Flexible, insulated wire leads

Printed circuit pins

W 1/

Printed circuit pins (edge mounted)

X 2/

Printed circuit pins (edge mounted, alternative configuration)

Y 3/

Printed circuit pins (staggered)

1/ The W terminals available only in essentially square styles. Pins extend from the edge 180o away from

the adjustment head and are parallel to the longitudinal axis of the adjustment screw.

2/ The X terminals available only in essentially square styles. Pins extend from the edge 90 away from the

adjustment head and are perpendicular to the longitudinal axis of the adjustment screw.

3/ Applicable only to style RT12.

1.2.1.5 Resistance. The nominal resistance value expressed in ohms is identified by a three digit number; the first

two digits represent significant figures and the last digit specifies the number of zeros to follow. The following are

examples of symbols for resistance values:

100 = 10 ohms

101 = 100 ohms

102 = 1,000 ohms

1.2.1.6 Example of PIN.

The PIN RT10C2P102 signifies:

Adjustment type, wire wound, variable resistor of the dimensions specified (see 3.1).

RT10

Having a resistance temperature characteristic of 0.005 percent (�50 ppm) per oC.

Having a temperature characteristic capable of operation at 85 C maximum and derated, at

150oC maximum (see 3.5).

Having printed circuit pins.

102

Having a nominal total resistance value of 1,000 ohms.