Turning outputs on or off through relay contacts is called __________.

The correct answer is that turning outputs on or off through relay contacts is called control logic. Control logic refers to the systems and processes that govern the operation of machinery and automation systems by managing how various inputs are transformed into outputs, effectively providing directions for how and when devices should be activated or deactivated.

In this context, using relay contacts to control outputs exemplifies how control logic operates in systems that utilize relays as components to execute commands based on specific conditions or inputs. The relay acts as an intermediary that can make decisions based on the information it receives from sensors or other inputs, thus executing control logic by switching the appropriate contacts to manage the system's operation.

The other options do not accurately capture this function as clearly. Relay activation might suggest a general action of turning on a relay, but it does not capture the logic-based nature of the control process involved. Signal modulation refers to varying a signal's properties to convey information but does not specifically relate to output control through relays. Circuit switching can imply the act of changing circuit paths but does not specifically mean controlling outputs through predefined logic as control logic does.