Glossary of Control Engineering Terms - R
Rate: Same as the derivative or "D" part of PID controllers.
Reference: In a closed loop system, the desired plant output that the controller tries to achieve. Also called the set-point.
Register: A storage location in a PLC.
Relay Ladder Logic: This programming language expresses a program as a series of "coils" and "contacts", simulating the operation of electromechanical relays. The resultant program is the equivalent of a Boolean equation, which is executed continuously in a combinatorial manner. The advantage of this language is the familiarity many electricians have with the simple operation of relays. Disadvantages include the complexity of large, cross-connected programs, and the difficulty of expressing such non-binary functions as motion control and analogue I/O.
Reset: Same as the integral or "I" part of PID controllers.
Right Half Plane: In the complex plane the half with positive real numbers. For continuous systems the poles in the right half plane are unstable.
Robust: A loop that is robust is relatively insensitive to process changes. A less robust loop is more sensitive to process changes.
Robust Control: A controller that is designed to be insensitive to process changes in terms of performance and stability. Usually achieved by modelling the expected changes in model parameters or bounds in the frequency domain.
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