Rockwell Automation Publication 1756-RM003N-EN-P - October 2011 515
Special Instructions (FBC, DDT, DTR, PID) Chapter 13
Description: The PID instruction typically receives the process variable (PV) from an
analog input module and modulates a control variable output (CV) on an
analog output module in order to maintain the process variable at the desired
setpoint.
The .EN bit indicates execution status. The .EN bit is set when the rung-
condition-in transitions from false to true. The .EN bit is cleared when the
rung-condition-in becomes false. The PID instruction does not use a .DN bit.
The PID instruction executes every scan as long as the rung-condition-in is
true.
Arithmetic Status Flags: Not affected
Fault Conditions:
Execution:
.DVPA BOOL Deviation is alarmed high (0=no; 1=yes)
.PVLA BOOL PV is alarmed low (0=no; 1=yes)
.PVHA BOOL PV is alarmed high (0=no; 1=yes)
Mnemonic: Data Type Description
Rung State
Execution of the PID instruction
.EN bit
These faults were major faults in the PLC-5 controller.
A minor fault will occur if Fault type Fault code
.UPD ≤ 0435
Setpoint out of range 4 36
Condition Action Action
Prescan The rung-condition-out is set to false. No action taken.
Rung-condition-in is false The rung-condition-out is set to false. N/A
Rung-condition-in is true The instruction executes.
The rung-condition-out is set to true.
N/A
EnableIn is set N/A EnableIn is always set.
The instruction executes.
Instruction execution The instruction executes the PID loop. The instruction executes the PID loop.
Postscan The rung-condition-out is set to false. No action taken.
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