SNAP PID MODULE REFERENCE
SNAP PID Module User’s Guide
23
Read-Only Variables
The following PID variables contain values that cannot be modified.
Process Hi
(also called
PV High
)
Sets the Process Hi alarm. If the Process Variable input
is greater than the Process Hi alarm, the Process Hi
and Process Quality flags are set. This occurs when the
PID is calculated. The Process Hi alarm must be greater
than or equal to the Process Lo alarm.
Range:
0 to 25000 (in raw counts)
27500
Manual or
Auto
Output Lo
(also called
Output
Low
)
Sets the Output Lo limit. If a PID output is calculated
that is below the Output Lo limit, the output is clamped
to the limit and the Output Lo flag is set. The Output Lo
limit must be less than or equal to the Output Hi limit.
Range:
0 to 4095
0
Manual or
Auto
Output Hi
(also called
Output
High
)
Sets the Output Hi limit. If a PID output is calculated that
is above the Output Hi limit, the output is clamped to the
limit and the Output Hi flag is set. The Output Hi limit
must be greater than or equal to the Output Lo limit.
Range:
0 to 4095
4095
Manual or
Auto
Output Slew Rate
Limits the maximum change in peak output that occurs
each time the PID is calculated. This variable can be
used to minimize PID overshoot when there is a large
change in a setpoint step. Changes to this limit take
effect the next time the PID is calculated.
Range:
0 to 4095
4095
Manual or
Auto
Output Limit
(also called
Output
Limit Deadband
)
This variable sets the minimum number of PID output
raw counts needed to cause the output to change. PID
changes that are less than or equal to the Output Limit
are ignored. This variable can be used to minimize wear
on control linkages. Changes to this limit take effect the
next time the PID is calculated.
Range:
0 to 4095
0
Manual or
Auto
Variable
Description
Status Flag
Hexadecimal word that indicates the state of PID module status flags. See
for bit descriptions.
Current PID
Process Variable used for the most recent PID calculation.
Last PID
Process Variable used for the second most recent PID calculation.
Oldest PID
Process Variable used for the third most recent PID calculation.
Current PID Error
Calculated PID error (Setpoint – PV) used for the most recent PID calculation.
Last PID Error
Calculated PID error (Setpoint – PV) used for the second most recent PID
calculation.
Output Change
Calculated change in PID output between most recent PID calculation and the
second most recent PID calculation in raw counts.
Variable
Description
Default
To Modify,
Use Mode...
