Operational DMD temperature and landed duty cycle interact to affect DMD useful life, and this interaction can be exploited to reduce the impact that an asymmetrical landed duty cycle has on the DMD useful life. This is quantified in the de-rating curve shown in Figure 5-1. The importance of this curve is that:

• All points along this curve represent the same useful life.
• All points above this curve represent lower useful life (and the further away from the curve, the lower the useful life).
• All points below this curve represent higher useful life (and the further away from the curve, the higher the useful life).

In practice, this curve specifies the maximum operating DMD temperature for a given long-term average landed duty cycle.