Which statement differentiates digital input from analog input on a PLC?

Which statement differentiates digital input from analog input on a PLC?

• A. Digital inputs are discrete on/off signals; analog inputs are continuous (4-20 mA, 0-10 V)
• B. Analog inputs are discrete on/off signals; digital inputs are continuous signals
• C. Digital inputs require no power; analog inputs require power
• D. Digital inputs are always less accurate than analog

Answer: (A)

Digital inputs provide a binary signal: a switch or sensor either makes a connection or it doesn’t, giving a discrete on/off state that the PLC reads as 0 or 1. Analog inputs, on the other hand, measure a signal that can vary continuously over a range, such as a current or voltage, which the PLC converts into a numerical value representing the process variable (for example, 4-20 mA or 0-10 V scaled to actual temperature, pressure, etc.). That distinction is what the statement highlights: digital inputs are discrete on/off signals, while analog inputs are continuous signals within a defined range. A helpful example is a door contact (digital) versus a temperature transmitter (analog). The other options mix up the nature of the signals, misstate power requirements, or claim a universal accuracy difference that isn’t correct.

Digital inputs provide a binary signal: a switch or sensor either makes a connection or it doesn’t, giving a discrete on/off state that the PLC reads as 0 or 1. Analog inputs, on the other hand, measure a signal that can vary continuously over a range, such as a current or voltage, which the PLC converts into a numerical value representing the process variable (for example, 4-20 mA or 0-10 V scaled to actual temperature, pressure, etc.).

That distinction is what the statement highlights: digital inputs are discrete on/off signals, while analog inputs are continuous signals within a defined range. A helpful example is a door contact (digital) versus a temperature transmitter (analog). The other options mix up the nature of the signals, misstate power requirements, or claim a universal accuracy difference that isn’t correct.