MIL-PRF-21038F
4.7.3.3 Ratio of transformation (turns ratio). The ratio of transformation of two windings shall be determined
by connecting the windings series aiding in the production of magnetic flux, applying a sinusoidal voltage to the
series configuration, and measuring the voltage ratio using a calibrated potentiometer and null meter or any
other suitable method may be used. The following details shall apply: Test frequency shall be high enough so
that the effect of any winding resistance unbalance will be negligible.
4.7.3.4 Polarity. Winding polarity shall be determined by comparing the voltages or impedances of
transformer windings when connected series aiding and series opposing and may be determined during the test
for ratio of transformation or any other suitable method may be used.
4.7.4 Dielectric withstanding voltage (see 3.7). Transformers shall be tested in accordance with MIL-STD-
202, method 301. The following details shall apply:
a.
Magnitude of test voltage and nature of test potential: (see 3.1).
b.
Duration of application of test voltage: 60 seconds minimum for qualification testing and 5 seconds
minimum for conformance inspection.
c.
Points of application of test voltage:
(1) For metal case transformers, between all windings.
(2) For nonmetallic case transformers, between windings.
4.7.5 Insulation resistance (see 3.8). Transformers shall be tested in accordance MIL-STD-202, method
302. The following details and exceptions apply:
a.
Test condition: As specified (see 3.1).
b.
Electrification time: One minute maximum.
c.
Points of application of test voltage:
(1) For metal case transformers, between all windings.
(2) For nonmetallic case transformers, between windings.
4.7.6 Resistance to soldering heat (see 3.9). Transformers shall be tested in accordance with test condition
MIL-STD-202, method 210. NOTE: Care should be taken to assure the lead length is not cut so short as to
preclude performance of the terminal strength test. The following details apply:
a.
Special preparation of specimen: Sample units shall not have been soldered during any of the
previous tests.
b.
Test conditions:
(1) Test condition C: (260°C ± 5°C; immersion, 10 seconds, ± 2 seconds) for transformers intended
for printed circuit board through hole mounting.
(2) Test conditions I, J, or K of MIL-STD-202 method 210 for surface mount.
(3) Test condition A or B for other types. For condition B, immerse to a point .125 inches (3.18 mm)
from the nearest insulating material or to one-half the exposed length of the terminal, whichever is
closer to the insulating material.
c.
Cooling time before final examination: 3 hours maximum.
4.7.7 Terminal strength (see 3.10). Transformers shall be tested in accordance with MIL-STD-202, method
211. The following details shall apply:
a.
Test condition: A.
b.
Points of measurement: A force shall be applied in the direction of the axis of the termination and shall
be increased gradually until the magnitude of the force specified (see 3.1) is reached.
4.7.8 Winding continuity (see 3.11). All windings of transformers shall be tested for electrical continuity by
any suitable means.
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