Which of the following would be an example of an Analog input?

• A. Limit switch
• B. Pushbutton
• C. Fuel level sensor
• D. Float switch

Answer: (C)

An analog input accepts a signal that can vary continuously, representing a variable quantity. In control systems this is usually a voltage or current that changes with the measured parameter. A fuel level sensor fits this because its output changes gradually with how full the tank is, giving a range of values for the reading (like 0–5 V or 4–20 mA).

The other devices are digital inputs: they provide a binary state—either on or off. A limit switch changes state at a fixed position, a pushbutton is a momentary contact, and a float switch typically opens or closes at a set level. Each of these yields a discrete, single value rather than a range, so they’re not analog inputs.