Glossary · Data, timing and communication
Polling
German: Polling
In systems engineering, polling is a communication pattern in which a system repeatedly requests current information from another system, typically at a fixed interval.
- Data and interfaces
- Integrated systems
In one sentence
Polling fetches current values at intervals; the polling rate sets the worst-case delay before a change is seen and must fit the use of the data.
Example
An HMI polls the PLC of a packaging machine every 500 ms for counters and alarm states, so an alarm can appear up to half a second late.
How it applies
- Integrated systems: The polling interval plus the response time is the worst-case latency until a change is seen. Short changes between two polls can be missed completely, so latch events that must not be lost.
- Functional safety: Polling detects a dead link quickly, because every missing response can trigger a timeout. Do not base a time-critical function on a polling rate that has not been included in its response-time calculation.
- Technical documentation: Interface documentation should state the polling interval, the load it creates and the maximum age of displayed values, so users know how current a screen is.
Polling vs. event-driven communication
Polling asks; event-driven communication reports changes when they occur. Polling gives predictable load and continuous proof that the link is alive; events reduce traffic when changes are rare. Many systems combine both.