Which device can serve as both an input and output component in a control circuit?

A programmable logic controller (PLC) serves as both an input and output component in a control circuit by processing data from input devices and controlling output devices based on that data.

In a control system, the PLC receives inputs from various sensors or switches that can be in the form of digital or analog signals. For example, it can read the status of inputs such as limit switches or temperature sensors. After processing this input information—based on the programmed logic—the PLC can then send commands to output devices, such as relays or actuators, to execute actions like turning on a motor or adjusting a valve.

This dual functionality allows the PLC to integrate and manage complex processes, making it a versatile component in automation systems. Its ability to handle both inputs and outputs seamlessly distinguishes it from the other options, which typically serve a more singular role within a control circuit.

For instance, while temperature switches, relays, and limit switches can act as input or output devices on their own, they do not have the capability to process information and make logical decisions like a PLC does. Thus, the unique role of the PLC in simultaneously managing inputs and generating outputs makes it the correct answer in this context.