A system where a process variable cannot send information to the final control element is termed what?

In the context of control systems, a process where the process variable cannot send information to the final control element is described as an open loop system. In an open loop configuration, the control action is independent of the desired output or the process variable. This means that the system operates without feedback; the input is set without regard to the actual output achieved.

In such systems, the desired outcome is not continually monitored or adjusted based on the system's performance. For example, when using an open loop control, a heater might be turned on for a specific amount of time without measuring the actual temperature; hence the control does not respond to the temperature changes.

In contrast, closed loop systems incorporate feedback that allows the output to be monitored and adjustments to be made to align with the desired set point. Feedback systems are critical in maintaining stability and precision in control processes. Cascade systems involve multiple control loops, where one control loop's output serves as the setpoint for another loop. Each of these options highlights an element of control processes, but for a system that lacks communication between the process variable and the control element, open loop is the accurate terminology.