Which of the following devices indicates to a control system that a vacuum system has reached the setpoint?

The device that indicates to a control system that a vacuum system has reached the setpoint is the vacuum switch. This component functions by monitoring the pressure within the vacuum system and is designed to provide an output signal when the pressure drops to a predetermined level, which is set as the desired vacuum level or setpoint.

When the vacuum reaches this specified point, the vacuum switch activates, allowing it to signal the control system that the necessary vacuum has been achieved. This feedback is crucial for automated systems to ensure that processes requiring a specific level of vacuum can proceed safely and efficiently.

The other options do play roles in the functioning of vacuum systems but do not serve the specific purpose of signaling the achievement of a setpoint. A vacuum generator is responsible for creating the vacuum, while an analog vacuum gauge provides a visual reading of the vacuum level but does not communicate directly with a control system. A vacuum relief valve helps maintain vacuum integrity by controlling pressure but does not indicate when the desired vacuum level is reached.