Basic reliability cookbook
Duty Cycle
Reliability
Duty cycle reliability is similar to standby reliability and is used when the active elements are inactive some of the time. The elements have a different failure rate when inactive than when active. It is typically used when the active elements are in warm standby (power off) and, as a consequence, have a lower failure rate than when they are active.
Given an element with
active failure rate
λ. For an
N% active duty cycle,
the active period failure rate
λA is
0.N *
λ and standby
period failure rate
λS
is (1-0.N) * 0.1 *
λ.
The combined failure rate
λDC
is
λA +
λS.
For example, an
element has a failure rate of 3 per million hours.
The reliability of the element while active for a fifteen year
lifetime is e(-3*0.1314)
= 0.454572. The reliability
of the element while in standby for a fifteen year lifetime is e(-0.3*0.1314)
= 0.961347.
λA = 3 * 0.3 = 0.9, λS = 3 * 0.1 * (1 - 0.3) = 0.21, λDC = 0.9 + 0.21 = 1.11
PDC
= e(-1.11*0.1314)
= 0.746987.
Note that PDC can be substituted for PP in the serial, parallel, k of n and standby reliability calculations.
Failure Rate | Serial Reliability | Parallel Reliability | K of N Reliability | Standby Reliability | Duty Cycle Reliability