Which method records data at a defined interval if the value or quality has changed?

The method that records data at a defined interval only if the value or quality has changed is known as Cyclic recording. This approach focuses on efficiency by minimizing unnecessary data collection. It is particularly effective in situations where it's crucial to monitor and log significant variations in the data rather than continuous or redundant samples of unchanging values.

Cyclic recording operates by taking samples at predetermined intervals, but it only saves these samples when there is a change in the data value or the associated quality indicators. This means that if the data remains stable over several intervals, it won't create new records, enabling a more streamlined data set that reflects only meaningful changes.

In contrast, other methods like Delta with swinging door and Delta with value deadband may record data based on thresholds (delta values) but in a different manner, focusing on specific types of changes rather than defined intervals. The Forced method records data regardless of any change, which would lead to more extensive and potentially less meaningful data collection. Thus, for efficient and relevant data logging based on set criteria, Cyclic recording is the optimal choice.