Characteristic value for machine availability. Efficiency (also use factoravailability factor) is the relation of the maximum and actually achievable value of a reference value such as machine efficiency. The efficiency is used for calculating the Overall Equipment Effectiveness (OEE).

The efficiency according to eq. 1 indicates the relation of actual operation time (operation time) and planned operation time (holding time) and serves as measure for downtime, adjustment and setting process losses. Since only operation time creates a value and is reimbursed by the market, a company has to have the goal to optimize this portion.

Eq. 1:

According to eq. 2, downtime is defined as follows:

Eq. 2:

Machine downtime can be determined automatically from the programmable logic controller (PLC) in the framework of notice and status capturing. There is a downtime distinction regarding the consideration of adjustment and setting times. With the OEE efficiancy, adjustment and setting times are regarded as organizational downtime, whereas with the NEE efficiency, adjustment and setting times are regarded as production time.

The holding time is defined on the basis of the VDI directive 3423 as shift length duration product in seconds multiplied with the number of shifts within a certain period. Planned (machine) breaks are subtracted from the total shift length duration.

VDI 3423 : 2002-01 Verf├╝gbarkeit von Maschinen und Anlagen (Begriffe, Definitionen, Zeiterfassung und Berechnung), Beuth Verlag, Berlin.
VDMA 66412-1: 2009-10 Manufacturing Execution Systems (MES) Kennzahlen, Beuth Verlag, Berlin.