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

3.5  Voltage rating.  Resistors shall have a rated direct current (dc) continuous working voltage, or an approximate sine wave root mean square (rms) continuous working voltage at commercial line frequency and waveform corresponding to the power rating, as determined from the following formula:

E =    PR

Where:   E = rated dc or rms continuous working voltage.

P = power rating (see 3.1). R = nominal resistance.

3.6  DC resistance.  When resistors are tested as specified in 4.7.2, the dc resistance shall be expressed in absolute ohms (see 1.2.1.4) and shall be within the specified initial resistance tolerance of the nominal resistance (see 1.2.1.5).

*                3.6.1  Resistance value deviations.  All maximum deviations as specified in this section are to be considered absolute limits with the exception of the contact resistance adjustments.

3.7  Short time overload.  When resistors are tested as specified in 4.7.3, there shall be no evidence of arcing, burning, or charring.  The change in resistance shall not exceed the initial resistance tolerance specified in the type designation (see 1.2.1.5) or ±(0.1 percent +0.05 ohm), whichever is smaller.

3.8  Thermal shock.  When resistors are tested as specified in 4.7.4, there shall be no mechanical damage.  The change in resistance shall not exceed ±(0.2 percent +0.05 ohm)

3.9  Solderability (not applicable to terminal type W).  When resistors are tested as specified in 4.7.5, they shall meet the applicable criteria for terminal evaluation in the referenced test method.

3.10  Resistance to solvents.  When resistors are tested as specified in 4.7.6, there shall be no evidence of mechanical damage and the marking shall remain legible.

3.11  Insulation resistance.  When resistors are tested as specified in 4.7.7, the insulation resistance shall be not less than 1,000 megohms.

3.12  Moisture resistance.  When resistors are tested as specified in 4.7.8, there shall be no evidence of breaking, cracking, spalling, or loosening of terminals or mounting hardware.  The final insulation resistance shall be not less than 100 megohms.  The change in resistance between the initial and final resistance measurements shall not exceed ±(1.0 percent +0.05 ohm) for styles RB70 and RB71, and

±(0.25 percent +0.05 ohm) for all other styles.

3.13  Dielectric withstanding voltage.  When resistors are tested as specified in 4.7.9, there shall be no evidence of flashover, mechanical damage, arcing, or insulation breakdown.  The change in resistance shall not exceed ±(0.05 percent +0.05 ohm).

3.14  Terminal strength.  When resistors are tested as specified in 4.7.10, there shall be no breaks in the wire lead terminals; the resistance element shall remain securely connected mechanically and electrically to the terminals in such a manner that the normal movement of the terminals shall not result in strain, wear, or damage to the element, coating, or enclosure.  The change in resistance shall not exceed

±(0.05 percent +0.05 ohm).

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