Glossary · Automation fundamentals, platforms and components
Signal
German: Signal
In automation and measurement, a signal is a physical quantity, such as a voltage, current, pressure or light, or its digital representation, that carries information about a state or value. Signals are classified as analog or digital (binary), and as inputs or outputs from the controller's point of view.
- Automation components
In one sentence
A signal is a physical quantity or its digital form that carries information, such as a 24 V input, a 4–20 mA value or a bus telegram.
Example
The limit switch provides a digital 24 V signal, while the level sensor provides an analog 4–20 mA signal to the same I/O module.
How it applies
- Engineering: I/O lists define each signal: tag, type (digital, analog, bus), direction, range, unit, source and destination. Signal quality includes noise, resolution and update rate.
- Commissioning: Loop checks confirm each signal end to end, from field device to HMI, before the plant starts.
- Documentation: Use one naming scheme for signals across diagrams, programs, HMI and manuals. Say whether a digital signal is active high or active low, for example a normally closed contact that is TRUE when healthy; this matters for wire-break detection and safety.
Signal vs. data
A signal is the carrier of information with a physical or timed character. Data is the stored or transmitted value with its meaning. An analog signal becomes data once it is sampled, scaled and given a unit.