Examples of Applied Control Types
Section
5-2
168
Note 5
Noninteracting control elements generally are one cause of lag.
Set Point
SP
PID control
Process
characteristics
+
−
PV
+
Control output
Set Point
SP
PID control
Process
characteristics
+
−
PV
+
−
Control output
−
Noninteracting contorl
element
Noninteracting contorl
element
5-2-3
Sample PI Control
When processes with prolonged dead time or an ON/OFF measurement
analyzer are taken as the control finite element, the next manipulated
variable is determined after the effect of having changed the manipulated
variable has sufficiently manifested itself.
PI control for time T1 is performed at every time T0, and resulting output is
held at a fixed value.
This is also called the "wait and see" method.
MV
T
1
T
0
T
1
T
0
Time
Function blocks used: ON/OFF Timer (Block Model 206)
Contact Distributor (Block Model 201)
(Step Ladder Program [Block Model 301] as
necessary)