Plant Historian OEE: frequently asked questions

OEE (overall equipment effectiveness) shows what share of the planned production time actually turns into good products. It combines the three types of loss – availability, performance and quality – into a single percentage.

OEE = availability × performance × quality. Availability = actual run time ÷ planned production time. Performance = (output × ideal cycle time) ÷ run time. Quality = good units ÷ total output.

A shift is planned at 480 minutes and the line stops for 60 minutes: availability 420 ÷ 480 = 87.5%. With an ideal cycle time of 1 minute, 380 instead of a possible 420 units are produced: performance 90.5%. 361 of them are good: quality 95%. OEE = 0.875 × 0.905 × 0.95 ≈ 75%.

85% is often cited as world class; many plants are well below that. How realistic a target is depends heavily on the industry, the equipment and the product mix. The trend of your own plant over time says more than a comparison with other people's figures.

Losses are usually grouped into the six big losses: equipment failures and setup and adjustment time reduce availability, idling with minor stops and reduced speed reduce performance, and start-up losses as well as scrap and rework reduce quality.

First, downtime must be recorded completely and classified by cause, such as setup, maintenance, fault or cleaning. Then the biggest sources of loss can be tackled in a targeted way and the measures tracked via the KPI in the continuous improvement process (CIP). Forwarding the machine status directly to maintenance and support staff also cuts response times.

Plant Historian OEE captures machine and production data, messages, faults and maintenance data centrally – via a standardised OPC link to the process control system or PLC, and via Modbus, M-Bus and 4–20 mA signals. Downtime is analysed and classified, and OEE is calculated and reported automatically.