MIL-DTL-83729C
6.1 Intended use. Electromechanical choppers are used in power supplies and special applications that require
conversion of a direct current voltage to a modified square wave of the same frequency and phase relationship to a
driving sine or square wave of alternating current.
6.2 Acquisition requirements. Acquisition documents must specify the following:
(a)
Title, number, and date of the specification.
6.2.1 Choppers covered by specification sheets.
(a)
Title, number, and date of the specification.
(b)
Title, number, and date of the applicable specification sheet and the complete PIN (see 1.2).
(c)
Packaging requirements (see 5.1).
Special or additional identification marking requirements (see 3.20).
(d)
6.2.2 Choppers not covered by specification sheets.
(a)
Title, number, and date of this specification.
(b)
The laboratory at which the inspection is to be performed (see 4.6).
(1)
(2)
Submission of samples and data (see 4.6).
(c)
(d)
Whether sand and dust, acceleration, barometric pressure (reduced) are applicable (see 3.12, 3.14, and
(e)
3.17).
(f)
Applicable vibration test.
(g)
Packaging requirements (see 5.1).
Special or additional identification marking requirements (see 3.20).
(h)
6.3 First article inspection. Information pertaining to first article inspection of products covered by this specification
should be obtained from the procuring activity for the specific contracts involved (see 3.2).
6.4 Intermetallic contact. The finishing of metallic areas to be placed in intimate contact before assembly presents
a special problem, since intermetallic contact of dissimilar metals results in electrolytic couples which promote
corrosion through galvanic action. To provide the required corrosion protection, intermetallic couples are restricted to
those permitted by MIL-STD-889.
6.5 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).
6.6 Subject term (key word) listing.
BBM Break-before-make.
Chatter A discontinuity of contact closure during dwell time (exclusive of bounce time) for periods exceeding 10 µs.
Chopper An electromechanical device for the production of modified square waves, of the same frequency as, and
bearing a definite phase relationship to a driving sine wave.
Common time In a MBB chopper, the angle in degrees that the contacts are all mutually closed.
Contact bounce Intermittent opening of contacts after the initial closing due to contact impact.
Dissymmetry The differential between the dwell time of the positive half cycle and the dwell time of the negative half
cycle.
Drive (also called coil voltage) In a chopper, the power supplied to a coil to cause action, usually measured in terms
of voltage and frequency.
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