GE VersaMax PLC User Manual page 276

Words
3
Sample Period
(Address + 2)
The shortest time, in 10 ms. increments, between solutions of
the PID algorithm. For example, use a 10 for a 100ms.
sample period.
4,5 Dead Band +
(Address + 3, Dead Band –
Address + 4) 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.
6 PID_IND: Proportional Gain (Kp)
(Address + 5) 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.
7 PID_IND: Derivative Gain (Kd)
(Address + 6) PID_ISA: Derivative Time (Td = Kd)
PID_IND: Change in the control variable in CV Counts if the
Error or PV changes 1 PV Count every 10 ms. Entered as an
integer representing a fixed-point decimal time in seconds
with two decimal places. The least significant digit represents
0.01 second (10ms.) units. Displayed as seconds with two
decimal places.
For example, Kd entered as 120 is displayed as 1.20 Sec and
results in a Kd * Δ Error / delta time or 120 * 4 / 3 contribution
to the PID Output if Error changing by 4 PV Counts every
30ms. Kd can be used to speed up a slow loop response, but
is very sensitive to PV input noise. This noise sensitivity can
be reduced by using the derivative filter, which is enabled by
setting bit 5 of the Config Word (later in this table)
PID_ISA: The ISA derivative time in seconds, Td, is entered
and displayed in the same way as Kd. Total derivative
contribution to PID Output is Kc * Td * Δ Error / dt.
276 GFK-1503E
For public disclosure
Parameter/Description Low Bit Range
Units
10 ms. 0 (every sweep) to
65535
(10.9 Min) At least
10ms.
PV Counts Dead Band +: 0 to
32767
(never negative)
Dead Band -: -32768
to 0
(never positive)
0.01 CV%/PV 0 to 327.67%
%
%CV / %PV
0.01 seconds 0 to 327.67 sec
VersaMax PLC User Manual