Chapter 7. PID Built-In Function Block
GFK-2950C
February 2018
347
7.2.2
Reference Array Parameters
Note:
Machine Edition software allows you to modify the configurable parameters for a PID
instruction in real time in online programmer mode. To customize PID parameters, right click
the PID function and select Tuning.
Words
Parameter/Description
Low Bit
Units
Range
1
(0)
Loop Number
Optional number of the PID block. It provides a common identification
in the CPU with the loop number defined by an operator interface
device.
Integer
0 to 255 (for
user display
only)
2
(1)
Algorithm
1 = ISA algorithm
2 = Independent algorithm
-
Set by the CPU
3
(2)
Sample Period
The shortest time, in 10ms. Increments, between solutions of the PID
algorithm. For example, use a 10 for a 100ms. Sample period.
Minimum time of 10ms is enforced by the block if the sweep<10ms)
10ms.
0 (every
sweep) to
65535
(10.9 Min) At
least 10ms.
4,5
(3,
4)
Dead Band +
Dead Band
–
Integral values defining the upper (+) and lower (-) Dead Band limits. If
no Dead Band is required, these values must be 0. If the PID Error (SP -
PV) or (PV - SP) is above the (-) value and below the (+) value, the PID
calculations are solved with an Error of 0. If non-zero, the (+) value
must greater than 0 and the (-) value less than 0 or the PID block will
not function.
Leave these at 0 until the PID loop gains are set up or tuned. A Dead
Band might be added to avoid small CV output changes due to
variations in error.
PV
Counts
Dead Band +: 0
to 32767
(never
negative)
Dead Band -: -
32768 to 0
(never
positive)
6
(5)
PID_IND: Proportional Gain (Kp)
PID_ISA: Controller gain (Kc = Kp)
PID_IND: Change in the control variable in CV Counts for a 100 PV
Count change in the Error term. Entered as an integer representing a
fixed-point decimal ratio with two decimal places. Displayed as a ratio
of percentages with two decimal places.
For example, a Kp entered as 450 is displayed as 4.50 and results in a
Kp * Error / 100 or 450 * Error / 100 contribution to the PID Output.
PID_ISA: Same as PID_IND.
Kp is generally the first gain set when adjusting a PID loop.
33
C
V
%
/
P
V
%
%CV/%PV
0 to 327.67%
Summary of Contents for PACSystems RSTi-EP
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