ABB C1900 Series - Page 29

27
10s 10s 5s 15s
Cycle Time
20s
Cycle Time
20s
Example shows a Cycle Time of 20 seconds
% Output =
On Time
Cycle Time
% Output =
10
20
x 100
x 100
% Output = 50%
% Output =
5
20
x 100
% Output = 25%
Mark Space
Mark
Space
Reverse Acting
Direct Acting
Set Point
100
0
% Output
50
==
50% Offset
0
% Proportional Band
1000
Set Point
100
0
% Output
50
0% Offset
0
% Proportional Band
1000
100
0
50
0
1000
Set Point
==
% Proportional Band
100
0
50
0
1000
Set Point
% Proportional Band
% Output
50% Offset
% Output
0% Offset
5 CONTROL OPERATION…
…5.9 Introduction to Standard Control
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.
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 Page in the
CONTROL CONFIGURATION LEVEL, Programming
Guide.
Fig. 5.15 Offset
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