The correct answer is: A controller, essentially, is a comparator.
A comparator is a device that compares two input signals and produces an output signal indicating which input is larger. It is a fundamental building block in many electronic circuits, and is used in a wide variety of applications, such as analog-to-digital converters, data acquisition systems, and control systems.
A sensor is a device that detects and responds to a physical stimulus such as light, heat, pressure, or sound. Sensors are used to measure physical quantities and convert them into electrical signals that can be read by a computer or other electronic device.
A clipper is a circuit that limits the amplitude of an input signal to a specified range. Clippers are used to protect circuits from overvoltage conditions, and to remove unwanted noise from signals.
An amplifier is a device that increases the power of an electrical signal. Amplifiers are used in a wide variety of applications, such as audio amplifiers, radio transmitters, and radar receivers.