MIL-PRF-28750F
p.
Status. An auxiliary, low-current switch segment of the SSR that indicates the condition of the SSR.
Examples of status are switch status (main switch open or closed); trip status (main switch turned off due to
overcurrent); flow status (minimum output current flowing); and B.I.T (built-in-test).
q.
Time, turn-off. The interval between the removal of input voltage and the output reaching 90 percent of its
ultimate change in voltage when the SSR is turned off.
r.
Time, turn-on. The interval between the application of input voltage and the output reaching 90 percent of
its ultimate change in voltage when the SSR is turned on.
s.
Trip. The automatic interruption of current which results from electrical overloads.
t.
Trip curve. The trip curve sets the minimum and maximum trip points of the SSR and is plotted as current
versus time, typically an inverse I²t relationship.
u.
Turn-on. The change in SSR condition (caused by the input voltage exceeding a predetermined minimum
turn-on voltage) resulting in the output changing from a nonconducting to a conducting state (or vice-versa).
v.
Waveform distortion. Improper silicon controlled rectifier gating circuit design can result in deviation from
the fundamental sinusoidal current or voltage waveform.
w. Zero crossover (ac SSR's only). A desirable characteristic in SSR's that switch ac voltages. This
characteristic is designed into the SSR to force it to turn on only near zero voltage and to turn off near zero
load current in the ac voltage and current cycles when connected in series with the load regardless of when
the input voltage is applied or removed. This design feature is beneficial in extending SSR life while
reducing radiated electromagnetic interference.
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 Application information. SSR's enjoy the advantages of sensitivity, bounce-free contact action, and indefinitely
long life in environments which do not exceed the voltage or temperature rating.
6.6.1 SSR/mounting surface interface. The interface between the SSR and its mounting surface should be given
special attention because most of the heat generated within the SSR must pass through this interface. To insure that
this interface passes as much heat energy as possible, while remaining relatively cool, the thermal resistance (degree
Celsius rise per watt dissipated within the SSR) between the SSR case and the mounting surface (especially for load
currents over 1.0 ampere) should be kept as low as possible.
6.7 Guidance documents.
6.7.1 Lead and terminal material. The following lead and terminal materials should be considered for meeting the
performance requirements of this specification (see 3.6.11.1):
a.
Type A: Iron-nickel-cobalt alloy: SAE-AMS-I-23011, class 1, ASTM F15.
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