Logix5000 Controllers General Instructions - SLAC Confluence

510 Special Instructions (FBC, DDT, DTR, PID)Where:VariableK PDescriptionproportional gain (unitless)K p = K c unitlessK i integral gain (seconds -1 )To convert between K i (integral gain) and T i (reset time), use:K iK C= ----------60T iK dderivative gain (seconds)To convert between K d (derivative gain) and T d (rate time), use:K d = K c (T d ) 60K CT iT dSPPVEBIASCVdtcontroller gain (unitless)reset time (minutes/repeat)rate time (minutes)setpointprocess variableerror [(SP-PV) or (PV-SP)]feedforward or biascontrol variableloop update timeIf you do not want to use a particular term of the PID equation, justset its gain to zero. For example if you want no derivative action, setK d or T d equal to zero.Anti-reset Windup And Bumpless Transfer From Manual To AutoThe PID instruction automatically avoids reset windup by preventingthe integral term from accumulating whenever the CV output reachesits maximum or minimum values, as set by .MAXO and .MINO. Theaccumulated integral term remains frozen until the CV output dropsbelow its maximum limit or rises above its minimum limit. Thennormal integral accumulation automatically resumes.Publication 1756-RM003I-EN-P - January 2007