MIL-R-93 Resistors, Fixed, Wire-Wound, Accurate, General Specification ForThis specification covers the general requirements for accurate, wire-wound, fixed resistors having a maximum resistance tolerance of 1 percent, with the winding protected against high humidity. The resistors are rated for continuous full load operation at any ambient temperature up to 125 Degrees C, and derated up to 145 Degrees C. They are not capable for application where alternating current ac characteristics are of critical importance. Performance characteristics are in accordance with table I.

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MIL-R-93F

4.7.11 Life (see 3.15). Resistors shall be tested in accordance with method 108 of MIL-STD-202 . The following details and exceptions shall apply:

a. Method of mounting for wire lead terminal resistors: Supported by their terminals. Axial lead resistors at a point 1 inch from the resistor body; printed circuit resistors at a point 3/4 inch from

the resistor body. Resistors shall be so arranged that the temperature of any one resistor shall not appreciably influence the temperature of any other resistor. There shall be no circulation of air

over the resistors other than that caused by the heat of the resistors.

b. Test temperature and tolerance: 125°C ±5°C.

c. Initial measurements: Measurements may be made inside or outside the chamber.

(1) Inside chamber: When measurements are made inside the chamber, the dc resistance shall be measured at a temperature of 125°C ±5°C after temperature stabilization and within 8 hours of exposure of the resistors to this temperature. This initial measurement shall be used as the reference temperature for all subsequent measurements under the same conditions.

(2) Outside chamber: When measurements are to be made outside the chamber, the measurement shall be made after units have been stabilized at room temperature for at least 8 hours. This initial measurement shall be used as the reference temperature for all subsequent measurements under the same conditions.

d. Operating conditions: Rated or maximum dc continuous working voltage shall be applied intermittently, one hour and 30 minutes "on" and 30 minutes "off" for 2,000 hours, at the test temperature. Each resistor shall dissipate rated wattage but shall not exceed maximum voltage. Adequate precaution shall be taken to maintain constant voltage on the resistor.

e. Test condition letter: Not applicable, test duration is 2,000 hours.

f. Measurements during test: Measurements may be made inside or outside the chamber. While the resistors are still in the oven, the dc resistance shall be measured as specified in 4.7.2, at the end of the 30 minutes "off" periods, after 250 hours +72 hours, -24 hours; 500 hours +72 hours, -

24 hours; 1,000 hours +72 hours, -24 hours; 2,000 hours +96 hours, -24 hours have elapsed. Measurement shall be made as near as possible to the specified time but may be adjusted so that measurements need not be made during other than normal work days.

(1) Measurements outside of chamber: When measurements are made outside the chamber, resistors shall be outside of the chamber, for a minimum of 45 minutes and stabilized before measurement.

g. Examination after test: Resistors shall be examined for evidence of mechanical damage.