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

4.8.4 Thermal shock (see 3.8). Resistors shall be tested in accordance with method 107 of

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

a. Mounting: In such a manner as to present a minimum obstruction to the airstream. In no case

shall the fixture prevent the specified ambient temperature from being achieved within 4 minutes

after the resistors are placed in the chamber.

b. Measurement before cycling: DC resistance shall be measured as specified in 4.8.5.

c. Test condition: B.

d. Measurement after cycling: Not less than 1 hour, but within a 24 hour period after the last cycle,

dc resistance shall be measured as specified in 4.8.5.

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

4.8.5 DC resistance (see 3.9). Resistors shall be tested in accordance with method 303 of

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

a. Measurement apparatus: Different types of measuring test equipment (multimeters, bridges, or

equivalent) are permitted to be used on the initial and final readings of this test, provided the

equipment is the same style, model, or if it can be shown that the performance of the equipment is

equivalent or better.

b. Limit or error of measuring apparatus: The maximum error of the measuring instrument shall not

exceed the lesser of:

(1) One-fourth the initial resistance tolerance +0.002 ohm.

(2) One-tenth percent of the measured resistance +0.002 ohm.

c. Measurement energy for electronic test equipment: The measurement energy applied to the unit

under test shall not exceed 10 percent of the 25�C rated wattage times 1 second.

d. Test voltage for bridges: Measurements of resistance shall be made by using the test voltages

specified in table XV. The test voltage chosen, whether it is the maximum or a lower voltage

which would still provide the sensitivity required, shall be applied across the terminals of the

resistor. This same voltage shall be used whenever a subsequent resistance measurement is

made.

e. Points of application of test voltage for initial resistance tolerance measurement (see 3.1):

Resistors of 10 ohms and less: .375 inch �.0625 inch (9.53 mm � 1.588 mm) from the end of the

body.

f. Temperature: The dc resistance test specified in group I of table IX shall be measured at 25�C

�2�C. For all other tests, unless otherwise specified herein, the temperature at which subsequent

and final resistance measurements are made in each test shall be within 2�C of the temperature at

which the first resistance measurement was made.