Statistics for Maintenance Modelling: Repairable Systems

# MCNF and MCCF¤

An equation which includes a variable raised to a power.

## MCNF

Let N(t) be the number of failures in the time interval (0, t), then:

MCNF = E(N(t)).

If this can be written in power law form as:

E(N(t)) = , we have:

ln MCNF = ln A + ln t

A plot of ln MCNF against ln t will reveal whether a power law is a suitable model for the MCNF. It also provides an estimate for via the slope of the fitted line. Signs of non-linearity may indicate an inadequate model, or features such as a 'kink' in the line may indicate a change in the system due, for example, to an effective quality improvement programme.

## MCCF

If C(t) is the cumulative cost at time t, then similarly we might be able to write:

MCCF = E(C(t)) = and

ln MCCF = ln B + ln t.