ABB C1900RC Operating Manual page 29

...5.9 Introduction to Standard Control
100
50
0
0
% Proportional Band
100
50
0
0
% Proportional Band
100
50
0
0
% Proportional Band
100
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
.
Guide
Fig. 5.15 Offset
50% Offset
Set Point
= =
1000
0% Offset
Set Point
1000
Reverse Acting
50% Offset
Set Point
= =
1000
0% Offset
Set Point
1000
Direct Acting
in the
Control Page
,
LEVEL Programming
5 CONTROL OPERATION...
Example shows a Cycle Time of 20 seconds
Mark Space
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 mark/
space ratio 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.
Mark
Space
5s 15s
Cycle Time
20s
5
% Output = x 100
20
% Output = 25%
x 100
27