Glossary · Automation fundamentals, platforms and components
Sampling time
Also known as: Sampling interval, Sample time
German: Abtastzeit
In digital control and measurement, the sampling time is the interval between two successive acquisitions of a signal value. It determines which signal dynamics can be captured and, in digital controllers, how often the control algorithm is executed.
- Automation components
In one sentence
Sampling time is the interval between two signal acquisitions; it limits which dynamics a digital measurement or controller can capture.
Example
The temperature loop runs with a sampling time of 500 ms, while the drive's current loop samples every 62.5 µs.
How it applies
- Engineering: The sampling rate must be well above the highest frequency of interest (Nyquist-Shannon theorem), and anti-aliasing filters prevent false low-frequency signals. For controllers, sampling time should be small compared with the process Time constant.
- Commissioning: PID parameters depend on the sampling time; changing a task's cycle time can detune a loop. Jitter in the sampling instant adds noise.
- Documentation: State the sampling time for each measured value in data logging, trends and interface specifications. A logged trend with 1 s sampling cannot show a 100 ms spike, which matters when logs are used as evidence.
Sampling time vs. scan cycle
The Scan cycle is how often the PLC program runs. A value may be sampled faster in the I/O module or slower in a dedicated task, so the two are not automatically the same.