MIL-DTL-917F(SH)
4.4.5 Insulation suitability test. Insulation suitability tests on insulated equipment shall be conducted as
specified in Appendix A.
4.4.6 Airborne and structureborne noise test. Airborne and structureborne noise tests shall be conducted in
accordance with the requirements of MIL-STD-1474 and MIL-STD-740-2 when specified in the individual
equipment specification.
4.5 Low quantity and non-Qualified Products List (QPL) qualified transformers and inductors. Where
transformers and inductors are not available as approved products under MIL-PRF-27, MIL-T-15108, MIL-I-1361,
MIL-PRF-21038, MIL-PRF-15305, MIL-T-16315, and MIL-T-17221, their use shall be approved by NAVSEA as
specified in 6.2 and 6.4. Low quantity transformers and inductors are defines as a number less than 100 units.
4.5.1 Inspection requirements for low quantity and non-QPL qualified transformers and inductors. All
transformers and inductors that are approved on the procedures of 6.4 shall be subjected to the following inspection
from the Group A inspection of MIL-PRF-27, except as modified herein.
a.
Visual and mechanical examination (external)
b.
Sealing
c.
Dielectric strength (except that the dielectric test voltage shall be not less than 500 Vrms)
d.
Induced voltage
e.
Insulation resistance
f.
Direct-current resistance
g.
Turns ratio
h.
Polarity
4.6 Temperature measurements.
4.6.1 Methods and procedures. Temperature measuring devices shall be carefully calibrated. The three
fundamental methods of temperature measurement and the procedures shall be as specified in 4.6.1.1, 4.6.1.2, and
4.6.1.1 Method 1. The "thermometer" method consists of the determination of the temperature by resistance
thermometers, alcohol thermometers, or by surface and contact thermocouples, any of these instruments being
applied to the hottest part of the equipment accessible. Mercury thermometers shall not be used. This method is
preferred for uninsulated windings, exposed metal parts, gases, and liquids. It is also preferred for surface
measurements generally and whenever other methods are not applicable or practical as in the case of some windings
with very low resistance. Thermocouples are preferred for measuring rapidly changing surface temperatures, as in
the case of resistors, commutators, collector rings, and other parts of rotating equipment.
4.6.1.1.1 Procedure. The number of thermometers or thermocouples used shall be liberal and shall be so
disposed as to ascertain the highest temperature. The thermometer bulbs or thermocouple contact points shall be
placed in such positions that they make the maximum practicable contact with the part whose temperature is to be
measured, and shall be so firmly supported that this degree of contact will not be altered by gravity and vibration.
The bulbs of thermometers shall be surrounded by a small amount of oil putty or equivalent to help maintain
contact. The probes of contact thermocouples shall be sufficiently sharp to penetrate any oxide film present on the
(metal) surface being measured.
4.6.1.2 Method 2. The "resistance" method consists of the determination of temperature by comparison of the
resistance of a winding at the temperature to be determined, with the resistance of the winding at a known
temperature. This method is preferred for insulated windings, except where measurements cannot be accurately
made due to uncontrollable resistance in contacts. Where it is impractical to make connections to obtain resistances
less than 1 ohm, a high accuracy instrument, such as a bridge with Kelvin contact terminals, shall be used.
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