Calculating uptime and downtime sounds easy enough, but once you get into the details, you realize there is a few more aspect to consider.
Uptime – Time when the machine is running
Downtime – Time when the machine is unavailable for production
Cycle Time – time it takes to complete an operation or set of operations. RS Production OEE will consider this the time to complete the operations assigned to the machine/-s being measured upon
Time per Piece – time it takes to produce one unit, including Availability, Performance and Quality losses. This time is relevant when preparing the production plan
RS Production specific vocabulary:
Optimal Cycle Time – This is the shortest time the machine needs to complete the assigned operation with the right quality. This should not be confused with average cycle time or “the fastest cycle time we usually run with”. Setting the right Optimal Cycle Time is crucial to get the correct Performance loss and hence the true OEE value. One machine can have several Optimal Cycle Times as it can vary with products.
Longest Cycle Time – This concept is what determines when a disturbance goes from being a Performance (speed) loss to an Availability loss in RS Production OEE. We recommend that you set this parameter at a minimum to 10 seconds, and if you have longer cycles you should be generous. See explanation below.
Production Stop Threshold – This concept determines when the stop goes from being a micro stop to a stop that should be given a stop reason.
There are several ways of capturing machine data and measuring your losses with RS Production OEE. The following description is relevant when using cycle signals.
How Optimal Cycle Time, Longest Cycle Time and Production Stop Threshold plays in to Performance and Availability losses.
Consequences of setting to short Optimal Cycle Time
When setting the Optimal Cycle Time to short, it will result in faulty losses and an incorrect OEE value (to low).
Consequences of setting to long Optimal Cycle Time
Setting the Optimal Cycle Time to long will result in hidden losses and indicate an incorrect higher OEE value.
Consequences of setting a too tight gap between Optimal Cycle Time and Longest Cycle Time
If you set this gap to tight, your Performance losses will be presented as Availability losses, and in the worst-case scenario, a stop will be reported for every product cycle. This can potentially burden the system and affect user experience.