Cutler-Hammer D320 PLC, User Manual

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D320 PLC User's Manual
Parameter Descriptions
Each parameter in the PID Loop data block provides a different function to the PID loop control. The
descriptions and purposes for each parameter are listed below.
STATUS REGISTER
Control Bits
Control Algorithm Defines PID equation used in calculation. Currently, the ISA form is not
yet supported, so this bit must be set to 0.
Normal/Reverse Oper. In Reverse mode (Bit = 1) the PID equation acts in the opposite direction as
the process value – that is, a positive error change in PV results in a
negative movement in CV. In Direct mode (Bit = 0), the action is in the
same direction.
Output Limiting When this bit is set, CV is limited by CVmax and CVmin. Otherwise, CV
will change over the entire possible range (0-32767).
Scaling Mode When set (Bit = 1), the Process Value and Control Value are scaled to an
application specific range, as defined by words 17 and 18 of the PID
parameter block. These scaled values are used for the PID loop calculation.
Derivative Term When set, the derivative term of the PID control equation is based on the
derivative of PV with time. When not set, the derivative term is based on
the derivative of the error value.
WindUp Function Enables the reset wind-up control. This can be used to limit an overreaction
to a large change in SV, or at startup.
Status Bits
Deadband State Bit is set when the PV is within the DB range of the SP.
CV Overrange Bit is set when the calculated CV is above CVmax.
CV Underrange Bit is set when the calculated CV is below CVmin.
Parameter Setting Bit is set under the following conditions:
PID Block Start Address (SR008) > 1792.
Scale Parameter Smin > Smax
Kp, Ki, Kd values are < 0.
Dt = 0.
CV Calculation is above maximum.
WindUp State Bit is set when the PID calculation is in WindUp (large accumulated error
term).