Distinguish analog and digital input/output (I/O) in a PLC.

Distinguish analog and digital input/output (I/O) in a PLC.

• A. Analog I/O measures continuous signals (for example 4-20 mA, 0-10 V); Digital I/O handles discrete on/off signals
• B. Digital I/O measures continuous signals; Analog I/O handles discrete on/off signals
• C. Analog I/O measures only voltage; Digital I/O measures current
• D. Digital I/O measures continuous signals; Analog I/O measures discrete signals

Answer: (A)

In PLCs, signals fall into two main types: continuous versus discrete. Analog I/O is built to read signals that can vary smoothly over a range, such as 4-20 mA current loops or 0-10 V voltage signals. These allow the PLC to measure exact quantities like temperature, pressure, or level. Digital I/O, on the other hand, deals with discrete on/off states, representing binary conditions such as a switch open/closed or a relay coil energized/deenergized. So the best description is that analog I/O measures continuous signals, while digital I/O handles discrete on/off signals. This contrasts with statements that mischaracterize one or the other—for example, digital I/O does not measure continuous signals, and analog I/O is not limited to a single voltage form or to current alone. This distinction helps you choose the right I/O module: use analog for sensors that provide a range of values, and digital for simple binary devices.

In PLCs, signals fall into two main types: continuous versus discrete. Analog I/O is built to read signals that can vary smoothly over a range, such as 4-20 mA current loops or 0-10 V voltage signals. These allow the PLC to measure exact quantities like temperature, pressure, or level. Digital I/O, on the other hand, deals with discrete on/off states, representing binary conditions such as a switch open/closed or a relay coil energized/deenergized.

So the best description is that analog I/O measures continuous signals, while digital I/O handles discrete on/off signals. This contrasts with statements that mischaracterize one or the other—for example, digital I/O does not measure continuous signals, and analog I/O is not limited to a single voltage form or to current alone. This distinction helps you choose the right I/O module: use analog for sensors that provide a range of values, and digital for simple binary devices.