Trend Test

By checking the trend, we will be able to understand if the machine is improving or deteriorating, i.e. DFR or IFR. The TBFs of the equipment in chronological order can be analyzed for the presence of trend to know whether the equipment or the item is deteriorating or improving with age.

By simply plotting cumulative TBFs against the cumulative number of failures we can test whether the machine or item under consideration is improving or deteriorating. If we get a curve concave upward, this means that the TBFs are becoming shorter and shorter that is to say, the machine is deteriorating. On contrary if we obtain a curve concave downwards, this means that the machine is improving. If the data exhibits linearity, the plot is said to have no trend and the failure data is known as independently and identically distributed (IID) and can be further analyzed by statistical distributions.

Eye Ball Analysis

In this we pass our eye through chronological TBFs and search for increase or decrease of the failure rate, i.e. if the TBFs are showing increasing in magnitude towards the end it shows decreasing failure rate. If the magnitude of TBFs is approximately constant throughout the period, then it shows constant rate of failure. If there are an increasing number of failures for each period then it indicates increasing failure rate and so on.