ABB COMMANDER 1911 Operating Manual page 29

...5.9 Introduction to Standard Control
50% Offset
100
50
0
0
% Proportional Band
0% Offset
100
50
0
0
% Proportional Band
50% Offset
100
50
0
0
% Proportional Band
100 0% Offset
50
0
0
% Proportional Band
Information. A control offset of 0% allows
early control of the output and reduces the
overshoot on initial start-up. Control offset is set
in the
Control
CONFIGURATION LEVEL
Fig. 5.15 Offset
Set Point
= =
1000
Set Point
1000
Reverse Acting
Set Point
= =
1000
Set Point
1000
Direct Acting
in the
Page CONTROL
, .
Programming Guide
5 CONTROL OPERATION...
Example shows a Cycle Time of 20 seconds
10s 10s
Cycle Time
20s
10
% Output = x 100
20
% Output = 50%
On Time
% Output =
Cycle Time
Information. The cycle time is the period
of oscillation (in seconds) of the output for time
proportioning control. The optimum value is a
function of the process characteristics.
Fig. 5.16 Cycle Time
Information.
• On/Off Control – use for applications where precise
control is not required or where frequent switching of a
contactor using time proportioning control causes
premature wear.
• Proportional Control – use where:
cycling action of on/off control is unacceptable
load changes are small or infrequent
offset can be tolerated or eliminated using manual
reset.
• Integral Action – introduce to the control system:
to eliminate offset automatically
if set point or load changes frequently
• Derivative Action – introduce to the control system:
to enable faster approach to the set point
(by enabling use of a smaller proportional band)
to minimize overshoot.
5s 15s
Cycle Time
20s
5
% Output = x 100
20
% Output = 25%
x 100
27