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

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 be applied

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

* d. Final measurements: Upon completion of step 6 of the final cycle, the resistors shall be conditioned at a temperature of 25°C ±2°C, and at a relative humidity of 90 percent to 95 percent for a period of 1 hour 30 minutes to 3 hours 30 minutes. After conditioning, the resistors shall be removed from the chamber and within 8 hours, the dc resistance shall be measured as specified in

4.7.2. Wiping and forced air drying prior to measurement is not allowed. The subsequent 4 hour to 24 hour conditioning period and measurements do not apply.

e. Examinations after test: Resistors shall be examined for evidence of breaking, cracking, spalling, and loosening of terminals and mounting hardware.

* 4.7.9 Dielectric withstanding voltage (see 3.13). This test shall be performed not less than 10 minutes, nor more than 30 minutes, after the preceding test (This time limit is not applicable to barometric pressure potion of 4.7.9.2).

* 4.7.9.1 Atmospheric pressure. Resistors shall be tested in accordance with method 301 of

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

a. Special preparations for wire lead terminal resistor: As specified in 4.7.7a. b. Initial measurement: Dc resistance shall be measured as specified in 4.7.2. c. Magnitude of test voltage: 500 volts rms.

d. Nature of potential: An ac supply at commercial line frequency and waveform. e. Duration of application of test voltage: 1 minute.

f. Rate of application of test voltage: The test voltage shall be raised from zero to 500 volts rms, as uniformly as practicable, at a rate of approximately 100 volts rms per seconds.

g. Points of application of test voltage: Between the resistor terminals connected together and the mounting hardware, or the V-block, as applicable.

h. Measurement after test: DC resistance shall be measured as specified in 4.7.2.

i. Examination after test: Resistors shall be examined for evidence of flashover, mechanical damage, arcing, and insulation breakdown.