Rockwell Automation 1772-L8_LW_LWP_LX_LXP,D17726.5.8 User Manual - Manual (Page 224)

EAF
Process Control Instructions
Chapter 16
16-13
Rung 1 This is a timing rung that toggles the block transfer. The
timing value (preset x time base) must equal the loop
update time of the PID instruction.
Rung 2 The Block Transfer Read instruction rung inputs the
process variable (PV), tieback (TB) and
feedforward/bias, if used.
Rung 3 The PID rung uses the block transfer done bit for
conditioning and two GETs representing the tieback input
and the process variable. The block transfer done bit gives
the needed false-to-true transition to cause the PID
instruction to calculate a new control output. Block transfer
and PID calculation are then synchronized and each
calculation is at the specified loop update time based on new
data. Once you select an address for the Data Addr, the EAF
automatically reserves the next 23 higher addresses for a
total of 24 addresses (30 octal).
Important: The two Gets shown in the PID rung (Rung 3) are mandatory
and must not be separated from the EAF by any other instruction.
The first Get contains data to be used as the tieback (TB) input. The
second Get contains the process variable (PV) input to the PID calculation.
The addresses of the two Gets do not have to be consecutive. You must
enter both Gets, even if TB is never used.
The EAF block contains the function number, a Data address, and a Result
address. The function number for the PID instruction is 27. The Data
address points to the PID control block. The control block contains a list
of parameters needed to solve the PID equation and select the PID control
options. The Result address points to the location of the control output
(CO) or output of the PID EAF.
Rung 4 This rung is a FIle-to-File Move used to display or input
equation parameters and set sign and status bits. The rung is
conditioned with a Branch End to ensure that the rung is
never executed.
Rung 5 The Block Transfer Write is used to relay the control
output to the final actuator. The File Address must be the
same as the Result Address in the EAF Block of the
PID rung.