MIL-PRF-28776F
4.8.17.2.1 Inductive load, dc. Unless otherwise specified (see 3.1), dc inductive loads shall be computed in
accordance with the following procedure:
a.
The relay shall be mounted in its normal operating position on a nonmagnetic plate with no immediately
adjacent metal.
b.
The load circuit shall be energized through a bounce free contact from a power supply regulated to within 5
percent of the specified rated voltage as shown on figure 10.
c.
By measuring the time for the current to reach 63 percent of its final value, the dc inductance is calculated
as:
L = Rt
Where:
L is the inductance in henries,
R is the resistance of the load circuit, and
t is the time in seconds for current to reach 63 percent of its final value.
4.8.17.2.2 Inductive load, ac. The load shall consist of inductive and resistive elements with 0.7 ±0.05 lagging
power factor at the voltage and frequency specified (see 3.1).
4.8.18 Life (see 3.23 and 6.10). Unless otherwise specified (see 3.1), relays shall be operated for 100,000 cycles
with contacts loaded in accordance with 4.3.3 and 4.8.18.1 through 4.8.18.4, as applicable. Relay coil energization
shall be nonsynchronous with the power supply for ac loads. Each relay case shall be connected to system ground
through an individual normal-blow fuse rated at the greater of 100 mA or 5 percent of load current. The ambient
temperature of the interior of the test chamber shall be +125°C minimum. The contact resistance or voltage drop, as
applicable, shall be monitored during 40 percent minimum of each "on" and each "off" period. The monitoring
equipment shall automatically hold the relay under test in the state in which the failure occurs (energized or de-
energized) and the contact voltage shall be removed. All contacts in each sample unit shall switch identical loads.
Following cycling, the electrical continuity of each case-grounding fuse shall be checked.
4.8.18.1 Resistive load. Cycling rate shall be 20 ±2 cycles per minute. Suitable resistors shall be used. Current
shall be rated resistive current as specified (see 3.1).
4.8.18.2 Inductive load. Cycling rate shall be 10 ±1 cycles per minute with approximately equal "on" and "off"
periods. Current shall be rated current. Appropriate inductive load components (see 4.8.17.2.1 and 4.8.17.2.2, as
applicable) shall be used. A suitable resistor may be placed in the circuit to obtain rated steady-state current flow.
Inductive load testing should be performed as recommended by MIL-HDBK-338 and approved by the qualifying
activity.
4.8.18.3 Lamp load. Unless otherwise specified, the lamp load shall be performed with a 28 V dc power supply
voltage. Either lamps or simulated loads may be used to provide the load as follows:
a.
Simulated loads shall subject the relays to making 12 times the rated lamp load and breaking the rated
lamp load. The duration of the 12 times inrush shall be 0.015 to 0.020 second. The total "on" time shall be
5 ±0.05 seconds and the "off" time shall be 5 ±0.05 seconds.
b.
Lamps shall be screened to verify a minimum initial cold inrush of 12 times the rated lamp load. Only lamps
meeting this requirement shall be used to provide load to the relays. The total "on" time shall be 2 ±0.05
seconds and the "off" time shall be 7 ±2 seconds.
4.8.18.4 Low level load. The minimum cycle time shall be 10X the sum of the maximum turn-on and turn-off (see
3.1) times for the relay under test. Each contact load shall be 10 to 50 µA at 10 to 50 mV (dc or peak ac). The coil
circuit shall be energized at rated coil supply voltage during 50 ±10 percent of each operation. Example: 10 x 8 ms
= 80 ms which would be a maximum of 12.5 cycles (one opening and one closure of a set of contacts) per second.
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