MIL-PRF-29C
6. NOTES
(This section contains information of a general or explanatory nature that may be helpful, but is not mandatory.)
6.1 Intended use. Resistors covered by this specification are intended for use as external resistors for 2.5 inch
(63.5 mm) and 3.5 inch (88.9 mm) voltmeters covered by MIL-PRF-10304 "Meters, Electrical Indicating, Panel Type,
Ruggedized, General Specification for", or in other high voltage application for which they may be found suitable.
O
Resistors of the power type, intended to operate at hot spot temperature in excess of 110 C, are not covered by this
specification. It is not considered good engineering practice to support these resistors except by their ferrules.
Resistors covered by this specification are unique due to the fact that these devices must be able to operate
satisfactory in military systems under the following demanding conditions: Undergoes a thermal shock, salt water
immersion, vibration, and mechanical strength test. In addition, these military requirements are verified under a
qualification system. Commercial components are not designed to withstand these military environmental conditions.
6.2 Acquisition requirements. Acquisition documents must specify the following:
Title, number, and date of this specification, and the complete PIN. (see 1.2)
a.
b.
Unless otherwise specified (see 2.1), the versions of the individual documents referenced will be those in
effect on the date of release of the solicitation.
c.
Packaging requirements (see 5.1).
6.3 Qualification. With respect to products requiring qualification, awards will be made only for products which are,
at the time of award of contract, qualified for inclusion in Qualified Product List QPL-29 whether or not such products
have actually been so listed by that date. The attention of the contractors is called to these requirements, and
manufacturers are urged to arrange to have the products that they propose to offer to the Federal Government tested
for qualification in order that they may be eligible to be awarded contracts or orders for the products covered by this
specification. Information pertaining to qualification of products may be obtained from Defense Supply Center,
Columbus, ATTN: DSCC-VQP, 3990 East Broad Street, Columbus, OH 43218-3990 or via the internet at:
6.4 Tin whisker growth. The use of alloys with tin content greater than 97 percent, by mass, may exhibit tin
whisker growth problems after manufacture. Tin whiskers may occur anytime from a day to years after manufacture
and can develop under typical operating conditions, on products that use such materials. Conformal coatings applied
over top of a whisker-prone surface will not prevent the formation of tin whiskers. Alloys of 3 percent lead, by mass,
have shown to inhibit the growth of tin whiskers. For additional information on this matter, refer to ASTM-B545
(Standard Specification for Electrodeposited Coatings of Tin).
6.5 Pulse applications. Designers are CAUTIONED on using these resistors in high power pulse applications.
Since they have not been qualified nor tested for such applications, damage and premature failure are possible.
These resistors only see a half hour (30 minute) short time overload as part of the group B inspection of this
specification.
6.6 Environmentally preferable material. Environmentally preferable materials should be used to the maximum
extent possible to meet the requirements of this specification. As of the dating of this document, the U.S.
Environmental Protection Agency (EPA) is focusing efforts on reducing 31 priority chemicals. The list of chemicals
and additional information is available on their website at https://www.epa.gov/osw/hazard/wastemin/priority.htm.
Included in the list of 31 priority chemicals are cadmium, lead, and mercury. Use of these materials should be
minimized or eliminated unless needed to meet the requirements specified herein (see Section 3).
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