Rockwell Automation 900-TC32 Digital Temperature Controllers, Series B - Manual (Page 404)

Publication 900-UM007D-EN-E - January 2011
D-6 Glossary
Process Variable: The parameter that is controlled or measured, such as
temperature, relative humidity, flow, and pressure.
Proportional Band: The range of temperature in which a manipulated
variable is proportionate to any deviation from the set point.
Proportional Control Action (P): A control action in which the manipulated
variable is proportionate to any deviation from the set point.
Proportional Period: A cycle of ON and OFF operations of the output relay
in a time-division proportional control action.
Proportional Control Plus Derivative Function (PD): A
time-proportioning controller that has a derivative function. The derivative
function monitors the rate at which a system’s temperature is either increasing
or decreasing and adjusts the cycle time of the controller to minimize
overshoot or undershoot.
Proportioning Control with Integral and Derivative Functions (PID): A
time-proportioning controller that has integral and derivative functions. The
integral function automatically raises the stabilized system temperature to
match the set point temperature to eliminate the difference caused by the
time-proportioning function. The derivative function monitors the rate of rise
or fall of the system temperature and automatically adjusts the cycle time of
the controller to minimize overshoot and undershoot. Also called
“three-mode” control.
Range: The difference between the lower and Upper-Limits of a
measurement quantity.
Rate Action (D): The controller senses the rate of change of temperature and
provides an immediate change of output to minimize the eventual deviation.
Remote Set Point: A remote set point allows a controller to receive its set
point from a source other than itself.
Reset (Auto Reset) Action: There is a manual adjustment that can be applied
to the offset by changing the configured value dial or moving the offset screw
on the control panel. The auto-reset function automatically adjusts the
configured value to eliminate offset.
Resistance Temperature Detector (RTD): A coil of wire, usually platinum,
whose resistance increases linearly with a rise in temperature. RTDs generally
have a higher accuracy rating than thermocouples.
Reverse Action: A control action in which the output power will be inversely
proportional to the deviation. An increase in the process variable will cause a
decrease in the output power, making this action suitable for a heating system.