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

4.8.16 Low temperature operation (see 3.20). Following the final dc resistance measurement specified

in 4.8.5, the resistors, mounted as specified in 4.8.15.1, shall again be placed in a cold chamber at room

temperature. The temperature shall be gradually decreased to -55�C +0�C, -0�C within a period of not

less than 1 hour 30 minutes. For conformance inspection only, and at the option of the manufacturer, the

resistors may be placed when the chamber is already at the extreme low temperature. After 1 hour of

stabilization at this temperature, full rated continuous working voltage as specified in 3.5.8 shall be

applied for 45 minutes. The resistors may be loaded individually or in parallel. Fifteen minutes +5

minutes, -0 minutes after removal of voltage, the temperature in the chamber shall be gradually increased

to room temperature with a period of not more than 8 hours. The resistors shall then be removed from

the chamber and maintained at a temperature of 25�C �5�C for a period of approximately 24 hours. The

dc resistance shall then again be measured as specified in 4.8.5. Resistors shall then be examined for

evidence of mechanical damage.

4.8.17 Life (see 3.21). Resistors shall be tested in accordance with method 108 of MIL-STD-202. The

following details and exceptions shall apply.

a. Mounting: Resistors shall be mounted on lightweight terminals. The effective length of each

terminal shall be .375 inch �.0625 inch (9.53 mm �1.588 mm). The method of attaching the

resistor leads to the terminals shall be at the option of the manufacturer. Resistors shall be so

arranged that the temperature of any one resistor shall not appreciably influence the temperature

of any other resistor. Regardless of the mounting and termination method selected, the integrity of

the connections to each resistor undergoing test shall be verified periodically to assure that each

part is tested with the voltage specified in 4.8.17d.

b. Test temperature: Qualification inspection and extended life testing: Ambient temperature

125�C +15�C, -0�C.

c. Initial measurements: 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 filtered or nonfiltered full wave

rectified ac voltage shall be applied intermittently, 1 hour 30 minutes "on" and 30 minutes "off", for

the applicable number of hours (see 4.8.17f), and at the applicable test temperature. "On time"

shall be 75 percent of the total elapsed time. During the "on" cycle, the voltage shall be regulated

and controlled to maintain �5 percent of the rated continuous working voltage.

e. Test condition: Two thousand hours for qualification inspection continued to 10,000 hours. Ten

thousand hours for FRL determination of group C.