ABB COMMANDER 1900 Series, User Manual

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5
2 CONTROL CONFIGURATION LEVEL…
• Ramp/Soak
2.1.3 Self-seeking Set Point – Fig. 2.5
The Self-seeking Set Point function reduces the delay between the end of a program and the beginning of the next program. The
process variable value is used as the program start point and the set point steps up to the process variable value. This has the
effect of changing the overall segment time and maintains a constant ramp rate.
2.1.4 Retort Function – Fig. 2.6
The Retort function ensures safe operation of retorts under fault conditions. When the process variable falls below the holdback
hysteresis value the program is put on ‘hold’ (as for normal operation). The set point then tracks the process variable until the
process variable starts to increase. The set point then ramps back up to the soak level at the rate of the previous ramp. When the
soak level is reached the program is released from its ‘hold’ state and depending on the retort mode selected either completes the
segment or repeats the entire segment.
The retort mode is selected in the
Ramp/Soak Profile Page
,
CONTROL CONFIGURATION LEVEL
.
2.1.5 Power Recovery Function
Note. The
Power Down Recovery Function
is only available on instruments fitted with the Timer option.
The Power Recovery function allows pre-selection of the restart position within a ramp/soak profile when power is restored after
a failure. If power is restored before the
Power Down Time
expires, the ramp/soak profile continues from the point at which power
failed. If power is restored after the
Power Down Time
has expired, the profile resumes from one of the following user-selected
points: start of the current program; start of the current segment or from the profile position at the time of failure. In all three cases
the controller restarts in
HOLD
mode. When power is re-applied to instruments not fitted with the Timer option, the profile is turned
off and control resumes at the local set point.
Fig. 2.6 Retort Function
Process Variable
Seg. 1 Seg. 2
Set Point
Program on Hold
Holdback
Hysteresis
Bandwidth
Segment either
completed or
repeated
Set Point Ramps
Back to Soak Level
at Previous Ramp
Rate
Equal to the value
set in Holdback
Hysteresis Frame
Fig. 2.5 Self Seeking Set Point
Set Point
Process Variable
Seg. 1 Seg. 2 Seg. 3
Current Process Variable
inserted as Program Start Level
Seg. 1 Seg. 2 Seg. 3 Seg. 1 Seg. 2 Seg. 3
Program
Start
Program
Start
Program
Start
Current Process
Variable Inserted as
Program Start Level