Glossary · Automation fundamentals, platforms and components
Sign of life (heartbeat)
Also known as: Heartbeat, Life sign, Keep-alive
German: Lebenszeichen
In industrial communication, a sign of life (heartbeat) is a signal or counter that a device or program sends periodically so that its communication partner can detect whether it is still active and communicating. If the sign of life stops changing within a monitoring time, the partner reacts, for example by going to a safe state.
- Automation components
In one sentence
A sign of life (heartbeat) is a periodic signal or counter that lets communication partners detect that a device or program has stopped.
Example
The PLC increments a heartbeat counter every 100 ms; if the robot controller sees no change for 500 ms, it stops the robot and reports a communication fault.
How it applies
- Engineering: Heartbeats detect frozen programs or lost connections that would otherwise leave Stale data in place. A toggling bit or incrementing counter is better than a constant value because a stuck value is detectable. The receiver monitors it with a Timeout or Watchdog.
- Commissioning: Test the reaction by disconnecting the cable or stopping the sender, and check that the specified Fault reaction occurs.
- Documentation: Interface specifications name the heartbeat signal, its update interval, monitoring time and the reaction on both sides.
Sign of life vs. safety protocol
A simple heartbeat shows that a partner is alive. Safety protocols such as PROFIsafe add further measures (for example sequence numbers, CRC and watchdog times) to detect communication errors to the level required for safety functions. A plain heartbeat on a standard connection is not a safety measure.