Which statement best describes the difference between analog and discrete input modules?

• A. Analog inputs handle continuous signals; discrete inputs handle digital on/off signals
• B. Analog inputs handle digital signals; discrete inputs handle continuous signals
• C. Both handle continuous signals
• D. Discrete inputs handle analog signals

Answer: (A)

The difference hinges on the type of signal each module handles. Analog input modules read signals that vary continuously within a range (for example, 0–10 V or 4–20 mA) and convert that varying value into a numeric reading the PLC can process. Discrete input modules, on the other hand, read binary states—on or off—coming from devices like switches or sensors, giving a simple 0/1 value with no intermediate levels. So the statement that analog inputs handle continuous signals while discrete inputs handle digital on/off signals accurately captures the fundamental distinction. The other options mix up these signal types or claim both handle continuous signals, which isn’t correct.