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

4.8.10 Moisture resistance (see 3.14). Resistors shall be tested in accordance with method 106 of

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

a. Mounting: Resistors shall be soldered by their leads to rigid mounts or terminal lugs. The spacing

of the mounts or terminal lugs shall be such that the length of each resistor lead is approximately

.375 inch (9.53 mm) when measured from the edge of the supporting terminal to the resistor body.

One half of the specimens shall be covered with a V-shaped strap whose width is such that the

resistor shall not extend more than .5 inch (12.7 mm) beyond the edge of the strap. The strap

shall be made of a corrosion resistant metal and shall be kept in contact with the resistor body by

supporting the resistor body as indicated on figure 2, with a nonconducting, noncorrosive support

whose width is less than that of the body and which will not act as a moisture trap. The mounting

straps may be individual for each resistor or continuous for all resistors.

b. Initial measurements: Immediately following the initial drying period, the dc resistance shall be

measured as specified in 4.8.5.

FIGURE 2. Mounting strap for moisture resistance test.

c. Polarization and loading voltage: The resistors shall be divided into two equal groups; one group

shall be subjected to polarization and the other group to load.

(1) Polarization: During step 1 to step 6 inclusive, a 100 volt dc potential shall be applied with the

positive lead connected to the resistor terminals tied together, and the negative lead

connected to the mounting hardware or polarizing straps, as applicable.

(2) Loading voltage: During the first two hours of step 1 and step 4, a dc test potential equivalent

to 100 percent rated wattage, but not exceeding the maximum rated voltage shall applied to

the resistors. Where potential to ground is over 250 volts, supplementary insulation shall be

provided.