Glossary · System coordination, integration and orchestration
Blocking signal
Also known as: inhibit signal, block signal
German: Sperrsignal
In industrial automation, a blocking signal is a signal by which one system prevents another system or function from starting or continuing a defined action until a condition is cleared. It is an operational coordination signal, not by itself a safety function.
- System integration
In one sentence
A blocking signal prevents another system from starting or continuing an action until a condition clears; on its own it is not a safety function.
Example
The robot cell sends a blocking signal to the infeed conveyor while it is re-gripping a part, so no new part is pushed into the pick position.
How it applies
- Engineering: Define the polarity and fail behavior of each blocking signal. A signal that blocks when true stops blocking when a wire breaks; many designers therefore use a “release” signal that must be actively present to allow motion.
- Safety: If blocking protects people, it must be implemented as a safety function with the required integrity, for example as an Interlock in the safety-related control system. A standard PLC bit is not sufficient for that purpose.
- Documentation: The interface description should state the source, the target, the meaning of each signal state and what happens on loss of communication. Make clear in manuals which blocking signals are functional and which are safety-related.
Blocking signal vs. interlock
A blocking signal coordinates processes. An interlock, in the machine-safety sense, prevents hazardous operation under defined conditions and is designed and validated as a protective measure.