ABB COMMANDER 1900 Series, Руководство по эксплуатации, Страница: 27 / 44

25
0
100
% Output
Set Point
1000
Reverse Acting
Output
0
Engineering Range
PB = 100.0%
PB = 200%
PB = 50%
PB = 50.0%
PB = 200.0%
PB = 100.0%
0
100
Set Point
1000
Direct Acting
Output
0
Engineering Range
% Output
5.9 Introduction to Standard Control
0 200 400 600 800 1000
500
60%
20%
1500 –500
200%
PV
Control
Set Point
Engineering Range
Examples shown with a Proportional Band Offset of 50%
Proportional Band Settings
Proportional
Band
Set
Point
50%
50% 80% 20%
Manual Reset Settings
PV
50%
80%
20%
80%
20%
5 CONTROL OPERATION…
Information. Proportional control gives an
output that is proportional to the deviation of the
process variable from the set point. The range
over which the output is adjusted from 0 to 100%
is called the proportional band and this is
expressed as a percentage of the engineering
range span.
Fig. 5.8 Proportional Control
Information. With Proportional Control (P
only or P and D) the controller may stabilize the
process at a value which is offset from the set
point. This offset can be removed using the
manual reset adjustment which effectively shifts
the Proportional Band.
Fig. 5.9 Manual Reset
Information.
• Reverse Acting – the output decreases as the process variable increases.
• Direct Acting – the output increases as the process variable increases.
Fig. 5.10 Control Action