Temperature Controller - Staveb AG

D-6 GlossaryProcess Variable: The parameter that is controlled or measured, such astemperature, relative humidity, flow, and pressure.Proportional Band: The range of temperature in which a manipulatedvariable is proportionate to any deviation from the set point.Proportional Control Action (P): A control action in which the manipulatedvariable is proportionate to any deviation from the set point.Proportional Period: A cycle of ON and OFF operations of the output relayin a time-division proportional control action.Proportional Control Plus Derivative Function (PD): Atime-proportioning controller that has a derivative function. The derivativefunction monitors the rate at which a system’s temperature is either increasingor decreasing and adjusts the cycle time of the controller to minimizeovershoot or undershoot.Proportioning Control with Integral and Derivative Functions (PID): Atime-proportioning controller that has integral and derivative functions. Theintegral function automatically raises the stabilized system temperature tomatch the set point temperature to eliminate the difference caused by thetime-proportioning function. The derivative function monitors the rate of riseor fall of the system temperature and automatically adjusts the cycle time ofthe controller to minimize overshoot and undershoot. Also called“three-mode” control.Range: The difference between the lower and upper limits of a measurementquantity.Rate Action (D): The controller senses the rate of change of temperature andprovides an immediate change of output to minimize the eventual deviation.Remote Set Point: A remote set point allows a controller to receive its setpoint from a source other than itself.Reset (Auto Reset) Action: There is a manual adjustment that can be appliedto the offset by changing the set value dial or moving the offset screw on thecontrol panel. The auto-reset function automatically adjusts the set value toeliminate offset.Resistance Temperature Detector (RTD): A coil of wire, usually platinum,whose resistance increases linearly with a rise in temperature. RTDs generallyhave a higher accuracy rating than thermocouples.Reverse Action: A control action in which the output power will be inverselyproportional to the deviation. An increase in the process variable will cause adecrease in the output power, making this action suitable for a heating system.Publication 900-UM003C-EN-E - January 2004