About Data Censoring in a Reliability Distribution Analysis

Censoring a datapoint means that the datapoint is excluded as a failure but included in the operating time of the piece of equipment. If you select the Censored check box, the data in the selected row is excluded. When you create a Reliability Distribution Analysis using a query or dataset as the data source, the GE Digital APM system automatically censors time values from the beginning of the Analysis Period to the first event and the time value from the last event to the end of the analysis. After the calculations for the analysis have been performed, each time that the query or dataset is refreshed, the censoring settings will be reset using the default criteria. Therefore, if you select a check box and refresh the data, the check boxes will no longer be selected.

Regardless of the data source you use, you can censor any failure data. Consider the following:

• For Maximum Likelihood Estimators (MLE), the maximum number of censored datapoints is one (1) less than the total number of datapoints.
• For Least Squares estimation, the maximum number of censored datapoints is two (2) less than the total number of datapoints.

Assume that you want to determine the reasons due to which a pump failed.

A pump might have failed due to multiple reasons, such as rusted part, motor overheating, insufficient power supply, or power outage. Each of these reasons will have its own specific failure rate and probability density function. To determine the failure rate of "motor overheating", you must censor all other failure modes from the analysis.

Further, motor overheating might be caused due to multiple reasons, such as improper operation, improper application, and improper maintenance. The censoring feature allows you to separate the failure modes, and determine which is the dominant failure mode. Based on this information, you can decide what is needed to improve the motor performance.

When you first create a Reliability Distribution Analysis, an automatically censored datapoint for each defined asset will appear on the plot. Each automatically censored datapoint represents the analysis End Date (specified on the Set Analysis Period window) for each defined asset.

GE Digital APM can:

• Censor failures automatically when it cannot calculate the time between events. For example, failure on a specific asset where the analysis does not contain a start date.
• Alert you that a datapoint is suspect. For example, in a Time to Failure type of distribution, an alert will be generated when the start date of an event overlaps the end date of a different event for the same asset. For this asset, suspect data is displayed in the Analysis Summary workspace.

Note: Although automatically censored datapoints appear on the plots, they do not appear in the Failures grid and, therefore, cannot be uncensored.

For a Reliability Distribution Analysis, when you pause on an automatically censored datapoint, the following information appears:

• Auto-Censored
• Name: Specified on the Assets tab of the Reliability Distribution Data Editor window.
• Installation Date: Specified in the Assets section of the Reliability Distribution Data Editor window.
• TTF value: Represents the time between the last failure date and the analysis End Date.