A Real-Time Approach to Process Control, 3rd Edition

Appendix B

Glossary of Terms

Actuator:

Portion of the valve that may be pneumatic or motor driven, used to open and close automatic valves.

Amplitude:

The difference between the average value of a sinusoidal variation and the maximum or minimum value.

Amplitude ratio:

The ratio of the amplitude of a system's response to its forcing function's amplitude when the forcing function is a continuous sinusoid; a form of dynamic gain.

Analog controller:

A controller that operates on continuous signals such as voltages, pressures or currents; this is a common older type of controller as distinguished from a digital controller.

Attenuation:

A decrease in the strength of a signal by a system component.

Automatic controller:

A device which operates to correct or limit the deviation of a variable from a reference value.

Automation:

The use of automatic control devices in a process so that human supervision is minimized.

Capacitance:

The amount of energy or material which must be added to a closed system to cause unit change in potential; the partial derivative of content with potential.

Cascade:

A series of stages in which the output of one is the input to the next.

Cascade control:

Automatic control involving ‘cascading’ of controllers; that is, having one controller's output as the input to the next controller instead of manipulating a process variable directly.

Comparator:

The portion of the control element which determines the difference between the set point and the measured feedback ...