Final answer:
The correct answer is a guard interlock, which is a safety device that stops a machine if a door is opened to prevent access to dangerous parts. It's a critical component in industrial safety systems.
Step-by-step explanation:
A sensor that stops a machine if a door is opened is categorized as a type of safety interlock designed to prevent accidental access to dangerous parts of a machine while it's in operation. The correct answer to this question is a guard interlock. A guard interlock is a device or system that ensures that the machine will not operate unless the guard or door is properly in place and closed.
This is a critical safety feature that can help to prevent injuries in industrial settings. An example of this would be a sensor attached to the protective door of a machine. If the door is opened the sensor sends a signal to the control system which in turn stops the machine from running. This creates a safer environment by ensuring the machine cannot operate when someone could be exposed to a potential hazard.