Rockwell Automation 900-TC32 Digital Temperature Controllers, Series B - Manual (Page 403)

Publication 900-UM007D-EN-E - January 2011
Glossary D-5
Loop Break Alarm: This alarm indicates a problem in the control loop, e.g., a
sensor has become disconnected or a problem has developed with the final
control element.
Manipulated Variable: The final output percentage (0
…100%) that will be
sent to a control element. This percentage can be related to a valve position, a
4
…20 mA signal, or the amount of ON time from a pulsed control output.
Manipulated Variable Limiting: A control option used when the process
cannot handle the full output of the heater or final control device. To limit the
manipulated variable, the user programs the controller so that it never sends a
100% output to the final control element.
Manual Mode: A selectable mode that has no automatic control aspects. The
user sets the output levels.
Multiple Set Points: Two or more set points independent from each other
which can be configured in the temperature controller.
National Electrical Manufacturers Association (NEMA): The United
States organization that establishes specifications and ratings for electrical
components and apparatus. Conformance by manufacturers is voluntary.
However, Underwriters Laboratories will test products to NEMA ratings for
operating performance and enclosure ratings.
National Institute of Standards and Technology (NIST): Formerly the
National Bureau of Standards, this United States agency is responsible for
establishing scientific and technical standards.
NEMA 4X: This enclosure rating specification certifies that a controller’s
front panel resists water washdown and is corrosion-resistant in indoor usage.
Normal Action: A control action which will increase the control output if the
process value is higher than the set point. This action is suitable for a cooling
system.
Offset: A controlled deviation (the difference in temperature between the set
point and the actual process temperature) remaining after a controlled system
reaches its steady state. The offset (droop) is created by the correlation
between the thermal capacity of the controlled system and the capacity of
heating equipment.
ON/OFF Control Action: A control action which turns the output fully on
until the set point is reached, and then turns off. Also called “two-position”
control action.
Overshoot: The number of degrees by which a process exceeds the set point
temperature.