Control Systems Glossary

A device that converts a control signal into physical action, such as a motor, valve, or heater element.

Bounded-Input Bounded-Output stability; every bounded input produces a bounded output.

A graphical representation of a control system showing functional blocks, summing junctions, and signal paths.

A frequency-domain plot of magnitude (dB) and phase (degrees) versus logarithmic frequency.

The polynomial equation obtained by setting the denominator of the closed-loop transfer function to zero; its roots are the closed-loop poles.

A control system that uses feedback from the output to adjust the input and correct errors.

A controller component designed to reshape the open-loop frequency response to meet stability and performance specifications.

The property that every state of a system can be driven to any desired state by an appropriate choice of input.

A dimensionless parameter (zeta) describing how oscillations decay; determines whether a second-order system is underdamped, critically damped, or overdamped.

The process of routing the system output back to the input for comparison with the reference signal.

The amount of gain increase (in dB) that can be tolerated before the system becomes unstable.

The output of a system when the input is a Dirac delta function; its Laplace transform is the transfer function.

A recursive optimal estimator that fuses model predictions with noisy measurements for linear Gaussian systems.

An integral transform that converts time-domain functions into s-domain functions, simplifying the analysis of LTI systems.

The frequency at which a second-order system oscillates in the absence of damping, denoted omega_n.

A polar plot of the open-loop frequency response G(jw) used to assess closed-loop stability via the Nyquist criterion.

The property that all internal states of a system can be inferred from the output measurements.

A control system that does not use feedback; the control action is independent of the output.

The amount by which the step response exceeds the final steady-state value, usually expressed as a percentage.

The additional phase lag at the gain crossover frequency that would bring the system to marginal instability.

The physical system or process being controlled, such as a motor, chemical reactor, or aircraft.

A graphical technique that plots the paths of closed-loop poles in the s-plane as a parameter (usually gain) varies.

The time required for the system response to remain within a specified percentage (commonly 2% or 5%) of the final value.

The difference between the desired and actual output as time approaches infinity.

The ratio of the Laplace transform of the output to the Laplace transform of the input for an LTI system with zero initial conditions.