Statistics for Maintenance Modelling: Repairable Systems

# Logs Plotted for Six Repairable Systems¤

This chart shows ln time plotted against ln MCNF and ln MCCF. Both plots are linear, indicating that a power law model is appropriate for both MCNF and MCCF. The slopes of the lines indicate how the rate of failures and costs are varying over time. In the case of MCNF, the gradient is approximately one and therefore the failure rate is fairly constant. The costs show a rate of change of 1.16 which indicates increasing costs, but given the length of time over which the data were collected, this factor may be purely due to inflation. This latter point shows that it is particularly important when costs are considered to measure them in the most appropriate way. Over a long period of time it may be necessary to use the concept of discounting or other different measures.