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4-178 Series 90-30/20/Micro Programmable Controllers Reference Manual – September 1998 GFK-0467K
4
Table 4-5. PID Parameters Details - Continued
Data Item Description
Manual
Command
(13)
This is an INT value set to the current CV output while the PID block is in Automatic
mode. When the block is switched to Manual mode, this value is used to set the CV
output and the internal value of the integrator within the Upper and Lower Clamp and
Slew Time limits.
Control Word
(14)
This is an internal parameter that is normally left at 0.
If the Override low bit is set to 1, this word and other internal SP, PV and CV
parameters must be used for remote operation of this PID block (see below). This
allows remote operator interface devices, such as a computer, to take control away
from the PLC program. Caution: if you do not want this to happen, make use the
Control Word is set to 0. If the low bit is 0, the next 4 bits can be read to track the
status of the PID input contacts as long as the PID Enable contact has power. A
discrete data structure with the first five bit positions in the following format:
Bit: Word Value: Function: Status or External Action if Override bit set to 1:
0 1 Override If 0, monitor block contacts below. If 1, set
them externally.
1 2 Manual/ If 1, block is in Manual mode; other numbers
Auto it is in Automatic mode.
2 4 Enable Should normally be 1; otherwise block is
never called.
3 8 UP/Raise If 1 and Manual (Bit 1) is 1, CV is being
incremented every solution.
4 16 DN/LowerIf 1 and Manual (Bit 1) is 1, CV is
being incremented every solution.
SP (15) (Non-configurable–set and maintained by the PLC) Tracks SP in; must be set
externally if Override = 1.
CV (16) (Non-configurable–set and maintained by the PLC) Tracks CV out.
PV (17) (Non-configurable–set and maintained by the PLC) Tracks PV in; must be set
externally if Override bit = 1.
Output (18) (Non-configurable–set and maintained by the PLC) This is a signed word
value representing the output of the function block before the application of
the optional inversion. If no output inversion is configured and the output
polarity bit in the control word is set to 0, this value will equal the CV output. If
inversion is selected and the output polarity bit is set to 1, this value will equal the
negative of the CV output.
Diff Term
Storage (19)
Used internally for storage of intermediate values. Do not write to this location.
Int Term
Storage (20/21)
Used internally for storage of intermediate values. Do not write to this location.
Slew Term
Storage (22)
Used internally for storage of intermediate values. Do not write to this location.
Clock (23–25) Internal elapsed time storage (time last PID executed). Do not write to these locations.
Y Remainder (26) Holds remainder for integrator division scaling for 0 steady state error.
Lower and
Upper Range
(27/28)
Optional INT values in PV Counts that define the highest and lowest display value for
the SP and PV Logicmaster Zoom key horizontal bar graph and ADS PID faceplate
display.
Reserved (29–34
and 35–39)
29–34 are reserved for internal use; 35–39 are reserved for external use. They are
reserved for GE Fanuc use, and cannot be used for other purposes.
Internal Parameters in RefArray