GE VersaMax PLC User Manual page 277

Words
8
PID_IND: Integral Rate (Ki)
(Address + 7)
PID_ISA: Integral Rate (1/Ti = Ki)
PID_IND: Rate of change in the control variable in CV Counts
per second when the Error is a constant 1 PV Count. Entered
as an integer representing a fixed-point decimal rate with
three decimal places. The least significant digit represents
0.001 counts per second, or 1 count per 0.001 second.
Displayed as Repeats/Sec with three decimal places.
For example, Ki entered as 1400 is displayed as 1.400
Repeats/Sec and results in a Ki * Error * dt or 1400 * 20 *
50/1000 = 1,400 contribution to PID Output for an Error of 20
PV Counts and a 50 ms. CPU sweep time (Sample Period of
0).
PID_ISA: The ISA Integral Time in seconds, Ti, must be
inverted and entered, as integral rate, as described for PID_
IND. Total integral contribution to PID Output is
Kc * Ki * Error * dt.
Ki is usually the second gain set after Kp.
9 CV Bias/Output Offset
(Address + 8) Number of CV Counts added to the PID Output before the
rate and amplitude clamps. It can be used to set non-zero CV
values when only Kp Proportional gains are used, or for
feed-forward control of this PID loop output from another
control loop.
10, 11 CV Upper Clamp
(Address + 9. CV Lower Clamp
Address + 10) Number of CV Counts that define the highest and lowest
value that CV is allowed to take. These values are required.
The Upper Clamp must have a more positive value than the
Lower Clamp, or the PID block will not work. These are
usually used to define limits based on physical limits for a CV
output. They are also used to scale the Bar Graph display for
CV. The PID block has anti-reset-windup, controlled by bit 4 of
the Config Word, to modify the integral term value when a CV
clamp is reached.
PID Built-in Function Block
For public disclosure
Parameter/Description Low Bit Range
Units
0 to 32.767
Repeats/
repeats/sec
0.001 Sec.
CV Counts -32768 to 32767
(add to PID output)
CV Counts -32768 to 32767
(Word 10 must be
greater than word 11.)
GFK-1503E User Manual 277