What is the principal control unit in a cabin pressurization system?

The principal control unit in a cabin pressurization system is the cabin outflow valve. This valve plays a crucial role in regulating the cabin pressure by allowing controlled exhaust of air from the cabin to the atmosphere. By opening and closing based on the altitude and pressure differences, it effectively manages the pressurization of the aircraft cabin.

The cabin outflow valve works in conjunction with other components of the pressurization system, such as pressure sensors and the environmental control system. It adjusts the cabin pressure to maintain a comfortable atmosphere for passengers and crew, ensuring safety and compliance with required altitude conditions.

While the other components listed, such as temperature sensors, pressure relief valves, and emergency pressure regulators, serve important functions within the overall pressurization system, they do not control the pressurization in the same manner as the cabin outflow valve. The temperature sensor monitors the air temperature, the pressure relief valve ensures that cabin pressure does not exceed safe limits, and the emergency pressure regulator provides an alternative means of maintaining pressure in case of a failure. However, none of these directly function as the principal control unit like the cabin outflow valve does.