MIL-PRF-94G
4.7.5 Solderability. Resistors shall be tested in accordance with method 208 of MIL-STD-202. The following
details shall apply (see 3.8):
a.
All three terminals shall be tested.
b.
No special preparation of leads is required.
c.
Steam aging shall apply.
d.
Terminals shall be dipped within 0.125 inch (3.18 mm) of body. All three terminals shall be dipped
simultaneously whenever possible. When configuration is such that terminals cannot be dipped
simultaneously, the 0.125 inch (3.18 mm) shall apply to the terminal on which ever it occurs when all three
terminals are dipped in an orientation which mostly meets the above requirement.
e.
Evaluation for tab terminals shall apply.
4.7.6 Resistance to soldering heat. Resistors shall be tested in accordance with method 210 of MIL-STD-202.
The following details shall apply (see 3.9):
a.
Measurement before test: DC resistance shall be measured as specified.
The temperature of the solder shall be 350 C ±10 C, and the duration of immersion shall be 5 seconds
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b.
±0.5 seconds.
c.
Depth of immersion in the molten solder: To a point 0.125 inch (3.18 mm) from the entry of the terminal into
the resistor body for resistor with a 0.250 inch (6.35 mm) diameter operating shaft and 0.0625 inch
(1.59 mm) for resistors with a 0.125 inch (3.18 mm) diameter shaft.
Measurement after test: 4 hours ±0.5 hours after completion of test, the dc resistance shall be measured as
d.
specified in 4.7.2. Resistors shall be examined for evidence of mechanical damage.
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4.7.7 Rotational life. Resistors shall be placed in a dry oven maintained at a temperature of 40 C ±5 C, for a
period of 24 hours ±4 hours. Following the removal from the oven, resistors shall be rotated 25 times to remove any
film, if any, under the contact arm. The total resistance of each resistor shall be measured. Resistor shafts shall be
continuously oscillated through not less than 90 percent of the total mechanical rotation at a rate of approximately 10
cycles per minutes, for a total of 25,000 cycles. The locking type resistors shall be rotated only 500 cycles. The rate
of rotation for conformance inspection shall be 10 cycles to 50 cycles per minute. Taper A resistors shall be ganged
in pairs and the resistors in each pair shall be connected in series so that a nominally constant current flows through
the resistors irrespective of the contact arm positioning during the rotation of the shaft as shown in figure 5. Care
shall be taken to insure that side thrust is minimized by proper alignment of the resistor shafts with the drive shafts.
When performing this test on locking bushing type resistors, the locking nut shall be removed. The shafts shall be so
connected mechanically that they turn simultaneously in the same direction. The potential applied during this test
shall be obtained from a dc power supply and shall be rated at the continuous working voltage of the resistor
(see 3.1). Resistors shall be monitored to ascertain that proper contact is made during and throughout the course of
the test. No potential shall be applied to tapers C and F resistors. Total resistance shall be measured at the end of
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cycling. At the conclusion of this test, resistors shall again be placed in a dry oven maintained at 40 C for 24 hours
±4 hours. Following removal from the oven, the total resistance shall again be measured and the percentage of
change in resistance from the initial measurement shall be computed (see 3.10).
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