Which of the following is an application of a relay?

A relay is an electromechanical device that acts as a switch controlled by an electrical signal, and it finds applications in various scenarios.

Performing control logic involves using relays to implement logical operations in electrical circuits. For instance, relays can work together to create complex combinations of operations, allowing for automated control in various systems.

The seal-in circuit is another application where relays maintain their own energized state once activated. This configuration is crucial in control systems, providing a way to keep the relay engaged even after the initial activation signal is removed, thus providing a stable control output.

Energizing a fluid power valve solenoid relies on relays to control the on/off state of solenoids that actuate valves in hydraulic or pneumatic systems. This role showcases the relay's ability to handle higher power loads or different voltage types that might not be suitable for direct interfacing with low-power control devices.

Given these applications, the answer that encompasses all these functionalities showcases the versatility and importance of relays in control systems and automation.