Guaranteed Dwell Time of Setpoint Programmer
(Original Document)
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At a Glance
A process' reaction to a setpoint change may be more or less rapid. The reaction does not necessarily follow the setpoint variation as calculated by the programmer. However, it is still possible to follow the evolution of a process value and to guarantee a dwell time at the selected setpoint: the dwell time countdown starts when the deviation between the setpoint and the process value is smaller than a previously defined threshold (THLD).
There are several manners to obtain the guaranteed dwell time:
In such instances, the dwell period countdown is "frozen" (interrupted) at each overflow.
Figure
The following figure illustrates the guaranteed dwell time.
Configuring a Guaranteed Dwell Time
Proceed as follows to configure a guaranteed dwell time.
Step
Action
1
Select a loop controller.
2
Select the Setpoint Programmer function.
3
Enable the function by checking the Guaranteed Dwell Time box.
4
Fill in the threshold value THLD and the type of overflow required:
  • high deviation, PV > dwell + THLD
  • low deviation, PV < dwell - THLD
  • high deviation, PV > dwell + THLD or PV < dwell - THLD
  • input deviation, deviation only at start of dwell.
5
In the GDT column, check the dwell time to which the function will be affected.
6
Enter the address of the process value you wish to monitor in the PV text area.
Note: Should you omit to provide the address of the process value, the Guaranteed Dwell Time function will not used, even if you have configured it. During execution, it is possible to inhibit this function by issuing a command.