Magnitude: See gain.

Manipulated Variable: The physical variable that is adjusted by the controller output (via the actuator) to cause the desired change in process output.

Manual Mode: In manual mode, the user sets the output.

Measurement: Same as "process variable." The variable you wish to control is usually measured but in many cases you measure one variable and from that infer another variable, which you do wish to control.

Measurement Noise: A disturbance which distorts the information obtained about the process from its sensors. Usually has a high frequency characteristic thus filtering should be used or the controller should have low gain at high frequency.

Measured Variable: The measurement of the process variable. Hopefully these two are the same, but filtering and calibration errors can cause a discrepancy between the actual process variable, and the measured variable used by the controller.

MIMO: Multi-input multi-output. See multivariable.

Mode: Auto, manual, or remote. In auto mode the controller calculates the output based its calculation using the error signal (difference between setpoint and PV). In manual mode, the user sets the output. In remote, the controller is actually in auto but gets its setpoint from another controller.

MMI: Man Machine Interface. Refers to the software that the process operator "sees" the process with. An example MMI screen may show you a tank with levels and temperatures displayed with bar graphs and values. Valves and pumps are often shown and the operator can "click" on a device to turn it on, off or make a setpoint change. Examples are Intellution's FIX DMACS, Wonderware's Intouch, Genesis's ICONICS, TA Engineering's AIMACS, and Intec's Paragon.

Multivariable: A system with more than one input and more than one output. Also called a MIMO system.

Multivariable Control: The design of a controller which is designed to explicitly consider all interactions or cross coupling in a plant both in terms of performance and closed-loop stability. The controller will have a matrix gain, that is each output will depend on more than one of the controller inputs.

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All of the information in this glossary has been carefully compiled and we believe it to be accurate. However, since any such definitions need to be placed in the context of specific applications, we assume no liability for the usage of information contained in this glossary.

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