A two-wire sensor is connected to which parts of the circuit?

• A. Controller input terminal and power supply
• B. Controller output terminal and ground
• C. Sensor and load
• D. Power supply and ground

Answer: (A)

A two-wire sensor is wired in series with the controller’s input, using the power source to provide the signal path. One lead from the sensor goes to the power supply, and the other lead goes to the controller input terminal. When the sensor activates, it completes the path from power to the input, allowing current to flow and the controller to detect a signal. The controller input is effectively the load in this arrangement, with the return path back to the supply completing the circuit.

That’s why the correct connection points are the controller input terminal and the power supply. Connecting to a controller output, or placing the sensor directly between power and ground without the input in the loop, wouldn't provide the sensed signal to the controller.