MIL-PRF-39005 Resistors, Fixed, Wirewound \(Accurate\), Nonestablished Reliability, Established Reliability, General Specification ForThis specification covers the general requirements for nonestablished reliability \(non-ER\), established reliability \(ER\), accurate, wire-wound, fixed resistors that have a maximum resistance tolerance of 1 percent and a high degree of stability with respect to time under specified environmental conditions. The resistors are capable for continuous full-load \(or voltage\) operation at any ambient temperature up to 125??C, and when derated, up to 145??C \(see 6.5\). They are not capable for application where the alternating current \(ac\) characteristics are of critical importance. ER resistors have life failure rates \(FR\) ranging from 1.0 percent to 0.001 percent per 1,000 hours \(see 1.2.1.5\). These FR are established at 60-percent confidence level on the basis of the life tests. The FR, identified by the appropriate symbol, is referred to operation at full rated voltage and temperature.

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MIL-PRF-39005G

4.8.2 Conditioning (see 3.6). Resistors shall be conditioned in accordance with method 108 of

MIL-STD-202. The following details and exceptions shall apply:

a. Method of mounting: Resistors shall be supported by their terminal leads. 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 heat of the resistors.

b. Temperature and tolerance: 125�C +15�C, -0�C

c. Initial measurements: At the manufacturer's option, measurements may be made inside or outside

the chamber.

(1) Inside the chamber: When measurements are to be made inside the chamber, the initial dc

resistance shall be measured after mounting at the applicable test temperature, after

temperature stabilization and within 8 hours of exposure of the resistors to the test

temperature. This initial measurement shall be used as the reference temperature for all

subsequent measurements under the same conditions.

(2) Outside the chamber: When measurements are to be made outside the chamber, the initial dc

resistance shall be measured after mounting at the room temperature. This initial

measurement shall be used as the reference temperature for all subsequent measurements

under the same conditions.

d. Operating conditions: Rated dc continuous working voltage or rated continuous working voltage

from an ac supply at commercial line frequency and waveform, intermittently, 1 hour 30 minutes

"on" and 30 minutes "off" for 100 hours +16 hours, -4 hours. Each resistor shall dissipate wattage

equal to the wattage rating of the resistor, but shall not exceed maximum voltage.

e. Measurement after conditioning: Leads may be cleaned before measurement:

(1) Inside the chamber: While resistors are still in oven, dc resistance shall be measured as

specified in 4.8.5 at the end of 100 hours +16 hours, -4 hours.

(2) Outside the chamber: When measurements are made outside the chamber, resistors shall be

stabilized before measurement.

f. Examination after conditioning: Resistors shall be examined for evidence of mechanical damage.

4.8.3 Short time overload (see 3.7). DC resistance shall be measured as specified in 4.8.5. Each

resistor shall be subjected to a dc test potential equivalent to that calculated for twice the rated wattage,

but not to exceed twice the maximum voltage (see 3.1), for 10 minutes under the following conditions:

a. In free air space, predicated on horizontal mounting with the resistor mounted in a minimum of .5

inch (12.7 mm) from any other resistor or the mounting base.

b. In still air, with no circulation other than that created by the heat of the resistors being operated.

Thirty minutes +15 minutes, -0 minutes after removal of the test potential, the dc resistance shall again be

measured as specified in 4.8.5. Resistors shall then be examined for evidence of arcing, burning, and

charring.