MIL-PRF-28776 Relays, Hybrid, Established Reliability, General Specification ForThis specification establishes the general requirements for relays that use a combination of solid state circuit input elements functioning with an electro-mechanical relay that performs the switching functions associated with control system applications \(see 6.1\). These relays are designed to operate in low and medium power switching circuits with contact ratings up to 1 ampere alternating current \(ac\) or direct current \(dc\). The failure rate level is established at a confidence level of 90 percent for qualification and 60 percent for maintenance of qualification based on 100,000 cycles at +125┬░C under rated load conditions specified herein. Excludes time delay relays. CAUTION: The use of any coil voltage less than the rated coil voltage will compromise the operation of the relay. CAUTION: Pick-up, hold, and dropout voltages are for test purposes only and are not to be used as design criteria. For additional application and caution information, see 6.1.

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MIL-PRF-28776F

4.8.7.8 Coil transient suppression (see 3.12.8).

4.8.7.8.1 Coil transient suppression (applicable to dc operated relays with internal coil transient suppression (see

3.12.8). The coil shall be connected as shown on figure 6 or by an equivalent test circuit.

NOTE: Voltage greater than the maximum specified may damage the coil suppression device.

The switching relay shall be a mercury wetted contact switching relay. E is the nominal operating voltage

for the relay under test. The switching relay is operated from a source voltage independent of E. CRO is

cathode-ray oscilloscope with a rise time of .020 �s or less. The horizontal (time) deflection scale shall be

set at 0.5 to 1 ms per division (0.5 to 1 ms/cm), and the vertical (voltage) deflection to be such that the

vertical gain provides accuracy in reading. Example: 5 V/cm for a 12 V back EMF limit, or 10 V/cm for a

24 V back EMF limit. Both horizontal (time) and vertical (voltage) deflection traces shall be of a calibrated

grid spacing such as cm or mm.

The source, E, shall be a low impedance source capable of delivering the rated coil voltage with no limiting

resistor or potentiometer used to regulate the line voltage.

The switching relay shall be closed for a minimum of ten times the turn-on time of the test relay, or

switching relay whichever is longer, to allow the oscilloscope and circuit network to stabilize and then

opened to obtain the induced voltage deflection trace. The relay is to be driven at a 10 �2 Hz cycling rate

with approximately equal open and closed times.

(1)

The reading shall be observed on the oscilloscope or other equivalent electronic test instrumentation.

The magnitude of the induced voltage transient shall be noted. A typical trace is presented on figure

(2)

The maximum value of three consecutive readings shall be noted.

For group A testing, only one measurement and other suitable test methods may be used to verify that the

back EMF (coil kick) is within the specified limit.

FIGURE 6. Coil transient suppression test circuit.