Glossary · Automation fundamentals, platforms and components
Rate of change (ROC)
Also known as: ROC, Rate-of-change alarm
German: ROC
In process control and monitoring, rate of change (ROC) is the change of a signal per unit of time, such as degrees per minute. ROC values are used for rate-of-change alarms, ramp limiting and detecting sensor faults or process upsets before absolute limits are reached.
- Automation components
- Process industry
In one sentence
Rate of change (ROC) is a signal's change per unit time, used for rate-of-change alarms, ramp limits and early detection of upsets or sensor faults.
Example
A reactor temperature alarm triggers when the temperature rises faster than 2 K per minute, long before the high-temperature limit is reached.
How it applies
- Engineering: ROC is calculated from successive samples, so it depends on the Sampling time and on filtering; noise creates false ROC alarms. A physically impossible rate of change is a common Plausibility check for sensor faults.
- Operation: ROC alarms give early warning of runaway reactions, leaks or blocked lines. Ramp limits restrict how fast setpoints or outputs may change.
- Documentation: Alarm documentation should state the ROC limit with its unit and time base, the filter used and the operator response.
Rate of change vs. absolute limit
An absolute limit alarms when a value is too high or low. A ROC alarm alarms when it changes too quickly, even within its normal range. The abbreviation ROC also has other meanings (for example the receiver operating characteristic in statistics), so spell it out at first use.