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.

Pages 1 - 2 - 3 - 4 - 5 - 6 - 7 - 8 - 9 - 10 - 11 - 12 - 13

MIL-PRF-28776F

4.8.7.2 Specified pickup, hold, and dropout voltages (turn-on voltage or current applied) (see 3.12.2). Specified

pickup, hold, and dropout voltages shall be measured as specified in 4.8.7.2.1, 4.8.7.2.2, or 4.8.7.2.3. Unless

otherwise specified (see 3.1), for qualification inspection, the relay shall be mounted in each of three mutually

perpendicular planes. For conformance inspection, the relay mounting position is optional. A suitable indicating

device shall be used to monitor contact position. During the test, all contacts shall not change state (break or

remake) when the coil is energized above the pull-in voltage, when the coil voltage is lowered to any value above the

specified hold (maximum) dropout voltage, or when the coil voltage is reduced from the (minimum) dropout voltage to

zero. It is permissible to perform specified pickup, hold, and dropout voltages using step function voltage changes as

specified in 4.8.7.2.1 or 4.8.7.2.2, and 4.8.7.2.3. Due to the fact that slow ramping will overheat relay coils and vary

specified pickup, hold, and dropout voltages, the step function method shall be the governing method in cases of

dispute.

4.8.7.2.1 Specified pickup voltage (turn-on voltage or current applied). The voltage shall be increased from zero

until the relay operates, and the specified pickup voltage shall be measured. It is permissible to perform specified

pickup, hold, and dropout voltage using a step function voltage changes as follows and as illustrated on figure 3.

Step up to the specified pickup value (voltage), contacts should have transferred and all normally-open

contacts should be making.

Increase to rated coil voltage.

Step down to specified hold voltage. Normally-open contacts must still be making.

Step down to specified dropout voltage, all contacts should have transferred and all normally-closed

contacts should be making.

Step down to zero voltage.

FIGURE 3. Pickup, hold, and dropout sequencing.

4.8.7.2.2 Specified hold voltage (turn-on voltage applied). Rated voltage shall be applied to the coil. The voltage

shall then be reduced to the specified hold voltage (see 3.1). All contacts shall not change state. It is permissible to

perform this test using the step function voltage program described in 4.8.7.2.1 and figure 3.

4.8.7.2.3 Specified dropout voltage (turn-on voltage applied). Rated voltage shall be applied to the coil. The

voltage shall then be gradually reduced until all contacts return to the deenergized position and the specified dropout

voltage shall be measured. It is permissible to perform this test using the step function voltage program described in

4.8.7.3 Coil current and coil resistance (see 3.12.3).

4.8.7.3.1 Coil current (see 3.12.3). When rated voltage is applied to the coil terminals the current must be within

the limits as specified (see 3.12.3.1). Apply at rated voltage for 5 seconds maximum.