Glossary · Electrical engineering and control panels
Analog input
Also known as: AI (I/O), Analog input channel
German: Analogeingang
In industrial control, an analog input is a controller input channel that converts a continuous signal, such as 4–20 mA, 0–10 V or a resistance thermometer signal, into a digital value the control program can process.
- Control panels
In one sentence
An analog input converts a continuous signal such as 4–20 mA or 0–10 V into a digital value for the control program.
Example
A pressure transmitter sends 4–20 mA to an analog input; the PLC scales the raw value to 0–10 bar and triggers a fault if the current drops below 3.6 mA.
How it applies
- Engineering: Choose the signal type, resolution, sampling time and filtering per channel. Live-zero signals (4–20 mA) allow wire-break detection; scale raw values to Engineering unit values in one consistent place.
- Installation: Use shielded cables, separate them from power cables and ground shields correctly to avoid noise; Galvanic isolation helps against ground loops.
- Documentation: For each channel, document signal range, scaling, unit, filter and fault behavior (wire break, overrange). Loop sheets and I/O lists are key references for commissioning and maintenance.
Analog input vs. digital input
An analog input measures a value over a range. A Digital input detects only two states. Some sensors offer both, such as a switching output and an analog output.