The PID function block combines all of the necessary logic to perform analog input channel processing, proportional-integral-derivative (PID) control with the option for nonlinear control (including error-squared and notched gain), and analog output channel processing.
The PID block provides enhanced control for applications in the following areas:
The PID function block supports mode control, signal scaling and limiting, feedforward control, override tracking, alarm limit detection, and signal status propagation. To support testing, you can enable simulation. This allows the measurement value and status to be supplied manually or from another block through the SIMULATE_IN input.
In Cascade (Cas) mode, the setpoint (SP) is adjusted by a master controller. In Automatic (Auto) mode, the SP can be adjusted by the operator. In both Cas and Auto modes, the output is calculated with a standard or series PID equation form. In Manual (Man) mode, the block's output is set by the operator. The PID function block also has two remote modes, RCas and ROut. These modes are similar to Cas and Man modes except that SP and OUT are supplied by a remote supervisory program.
The PID function block can be connected directly to process I/O (in DeltaV, but not in fieldbus devices). It can also be connected to other function blocks through its IN and OUT parameters for cascade and other more complex control strategies.
You connect BKCAL_OUT to an upstream block's BKCAL_IN to prevent reset windup and provide bumpless transfer to closed loop control.
You can connect the tracking input (TRK_VAL) for externally controlled output tracking.
BKCAL_IN is the analog input value and status from a downstream block's BKCAL_OUT output that is used by a block for bumpless transfer. This connection is necessary if the PID is a master to another controller in a cascade. Without the connection the slave controller will not make the transition to CAS and the master PID will never be active.
CAS_IN is the remote SP value from another block.
FF_VAL is the feedforward control input value and status.
IN is the connection for the process variable (PV) from another function block.
SIMULATE_IN is the input value and status used by the block instead of the analog measurement when simulation is enabled.
TRK_IN_D initiates the external tracking function.
TRK_VAL is the value after scaling applied to OUT.
BKCAL_OUT is the value and status sent to an upstream block to prevent reset windup and provide bumpless transfer to closed loop control.
OUT is the block output value and status.
The following diagram shows the internal components of the PID function block. The parameters may vary slightly for extended blocks.
