<Appendix 5. PID Block>
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IM 01E21A02-03EN
A5.2 Functions of PID Block
The control calculation processing provided in the PID block has the following functions.
Control Calculation
Processing
Description
PID control
Calculates the control output using the PID control algorithm.
Control output action
Converts the change in control output (ΔMV) for each control period to the
manipulated value (MV) that is to be actually output.
Supports “velocity type” as an operation of operational output.
Direction of control action Switches the action direction of output between forward and reverse based on the
changes in the deviation.
Control action bypass
When the bypass is set, the SP value is scaled to the OUT range and output as
OUT.
Feed-forward
Adds the external compensation value FF_VAL to the output signal from the PID
computation.
Measured-value tracking
Equalizes the setpoint (SP) to the measured value (PV).
Setpoint limiter
Limits the value of setpoint (SP) within the high/low limits.
External-output tracking
Converts TRK_VAL to the scale of OUT and outputs it.
Mode change
The PID block has the following eight modes: O/S, IMan, Lo, Man, Auto, Cas, RCas,
and ROut.
Bumpless transfer
Switches the operational output value (OUT) without a sudden change at changing
block modes and switching the operational output value (OUT) at the cascade
downstream block.
Initialization and manual
fallback
Changes MODE_BLK to IMan and temporarily suspends the control action.
Operates when initialization and manual fallback conditions are met.
MAN fallback
Changes MODE_BLK to the Man mode and temporarily aborts the control action
forcibly.
Auto fallback
Changes MODE_BLK to Auto when MODE_BLK is running in the Cas mode, and
continues the control action using the setpoint set by the operator.
Mode shedding
Specifies the block mode with SHED_OPT after a failure.
Block alarm processing
Supports block alarms, process alarms, and event updates.
