Control Operation; Operating; Set Point Tracking; Auto/Manual Transfer - ABB COMMANDER 1911 Operating Manual

...5 CONTROL OPERATION

5.1 Operating Page Introduction

5.1.1 Set Point Tracking

With set point tracking enabled (
) the local set point value tracks the
CONFIGURATION LEVEL
process variable when the controller is in Manual control
mode. In this mode of operation the set point limits do not
apply. If the set point value is outside its limits when Automatic
control mode is selected, the local set point remains outside its
limits and can only be adjusted in one direction, towards its
limits. Once inside the limits they apply as normal.
With remote set point tracking enabled, the local set point
tracks the remote set point value when in the remote set point
mode. In this mode of operation the local set point limits do not
apply. If the set point value is outside its limits when the local
set point value is selected, the local set point remains outside
its limits and can only be adjusted in one direction, towards its
limits. Once inside the limits they apply as normal.

5.1.2 Auto/Manual Transfer

All auto-to-manual transfers are bumpless. If the local set point
is used and set point tracking is enabled, all manual-to-auto
transfers are bumpless, since the set point is always at the
same value as the process variable. Without set point tracking
enabled, the response following a manual-to-auto transfer
depends on the control settings. With an integral action setting
the output is ramped up or down to remove any process
variable offset from the set point (providing the process
variable is within the proportional band). If the integral action is
off, the output may step to a new value when the controller is
transferred back to automatic control mode.
With remote set point tracking enabled, the control set point
switches automatically from remote to local when manual
mode is selected.
5.1.3 Profile Control – Fig. 5.3
Overall Profile
Segment
Numbers
Eng.
Units
S1 S2
T1 T2
Program 1
Start
at
SS
Start at S2
Fig. 5.3 Overall Profile Example
12
Set Points Page, CONTROL
S3 S4 S5
Time
T3 T4 T5
End
at S3
Program 2
End at S5

5.1.4 Cascade Control

The master in a cascade set-up is always channel 1 and the
slave is always channel 2. If the slave is switched to manual
control with cascade set point selected, the slave's set point
reverts automatically to local set point.
Ratio and bias are applied to the master output value so that
the slave's cascade set point value = Ratio x Master Output +
Bias.
With
Output Tracking enabled
manual mode or local set point, the master is switched
automatically to manual. The manual output of the master
tracks the local set point value of the slave. The value fed back
to the master takes into account any ratio and bias settings.
With
Output Tracking disabled
mode or local set point does not affect the operation of the
master.
To return to full cascade control carry out the following
procedure:
a) Switch the Slave controller into automatic control mode.
b) Switch the Slave Controller set point to 'Cascade'.
c) Switch the Master controller to automatic control mode (if
currently in Manual)
5.1.5 Heat/Cool Control – Fig. 5.4
When in automatic control mode both the heat and cool
outputs are turned off when in the Output Off Hysteresis Band.
In manual control mode the Output Off Hysteresis Band has no
effect. If the P.I.D. output is within the Off Hysteresis Band
when the controller is returned to auto control mode, the Off
Hysteresis Band has no effect until either the P.I.D. output
goes outside the band or becomes equal to the Crossover
Value.
100%
Output Off
Hysteresis
Cool
Output
0%
Crossover
Controller Output
0%
Fig. 5.4 Heat/Cool Control – Principle of Operation
– if the slave is switched to
– switching the slave to manual
100%
Heat
Ouput
0%
Value
100%