Time-based Availability considering the operating time and restoration time

Time-based Availability considering the operating time and restoration time

The second paragraph of point 4.9 of the EN 13306 standard provides an example of one another approach to quantify the time-based availability. The definition is:

Ratio, during a given period, of the operating time (OT) to the sum of operating time and the time to restoration (OT+TTR)

This ratio, for a given period, expresses as a percentage the proportion of the period in which the unit was able to perform according to expectations, except for those periods when the equipment was not available due to a fault.



It is necessary to clarify the concepts of Required time, Non required time, and restoration time (TTR time to restoration). The expected time is the part of the calendar time during which the device should be operational and suitable to perform the required function according to the production or service plan. According to point 9.21 of the EN13306:2017 standard, the recovery time lasts from the moment of failure to recovery, i.e., until the moment the device regains the ability to perform the required function. The recovery time is therefore the duration of the repair intervention following the failure and does not include the time required for other preventive maintenance interventions.

The „Down state” period shown in the attached figure lasts from the moment of failure until the performance of the device is restored. It includes the time elements of all the activities that are part of the repair intervention, which include error detection, preparation, active intervention, measurements, function tests, etc. require, including delays attributable to possible administrative reasons.

The EN15341 standard calls this indicator M12, Availability based on time to restoration