C6-17
IM 34M06H62-02E 2nd Edition : June 2008-00
Reference Deviation
The Reference Deviation (RDV) parameter allows you to switch between PID parameter
groups according to the magnitude of the deviation.
When the difference between the PV and CSP is larger than the value of the Reference
Deviation (RDV) parameter, the PID parameter group intended for large deviations is
selected (PIDNO = 4).
For instance, when the deviation is large, proportional band can be reduced to bring the
PV to the CSP more quickly.
PID parameter group switching by the Reference Deviation (RDV) parameter has priority
over switching by the Reference Point (1RP, 2RP) parameters. In addition, when the
deviation falls below the Reference Deviation (RDV), operation reverts to using the Zone
PID parameter group corresponding to the PV at that point.
The Zone Switching Hysteresis (RHY) parameter applies when a switchover from PID
parameter group 1, 2 or 3 to PID parameter group 4 is made due to reference deviation.
Table C6.11 Parameters Related to Reference Deviation
Data Position Number
Symbol Description Unit Data Range
Default
Value
Attribute
Stored
Loop1 Loop2 Loop3 Loop4
189 389 589 789 RDV Reference deviation Industrial unit
0 to (PRH-PRL)
Setting to 0 disables the
reference deviation function.
0 RW
Figure C6.16 Reference Deviation Selection
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