Usage Downtime Editor

Usage downtimes are used to model downtimes that occur after a location has been operating for a certain amount of time, such as if a machine fails due to wear after so many hours of operation. Usage downtimes are different from clock downtimes because usage downtimes are based on location operation time, which does not include blocked time. Clock downtimes are based on total elapsed simulation time (operation time, blocked time, idle time). Usage downtimes are available only for single-capacity locations.

The Usage Downtime Editor consists of the edit table shown below. It contains fields for defining location downtimes based on the actual time in use. Most functions, including distributions can be included in the Frequency, First Time, and Priority fields. (See the Appendix A to see if a specific function is valid in a particular field.)

Frequency The usage time between downtimes.

First Time The time in use before the first downtime occurrence. Leave blank if the first time is to be based upon the frequency entered.

Priority The priority, between 0 and 999 of the downtime. The default priority is 99, which is the highest non-preemptive priority. Generally, usage downtimes tend to be preemptive and should have priority values greater than 100.

Logic Any logic statements to be processed when the downtime occurs. Typically, this field contains a time expression representing the length of the downtime. Click on the heading button to open a larger edit window.

Disable Select YES to temporarily disable the downtime without deleting it from the table.

In this example, Robot2 will experience breakdowns according to a Gamma distribution with shape and scale parameters 1.7 and 2.3. Maintenance resource M1 will be used to service the robot. The repair time is normally distributed with a mean of 2.4 minutes and a standard deviation of .3 minutes.

Please note

Usage-based downtimes do not accumulate. For example, if a downtime cannot occur because the priorities of the entities being processed are at least 2 levels higher than the priority of the downtime, only the first downtime resumes after processing the entities. All others are ignored.