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Manual
-
Two-position controller with feedback
In modern two-position controllers with feedack -- such as the SIPART DR21 -- the
switching response is determined by the period, the system deviation and the para-
meters. The period T is set as a fixed value in the controller. The system deviation xd in
conjunctionw ith the parameters Kp/Tn/Tv determines the duty factor (ON/OFF ratio)
within the period. Thus the switching response of the controller is not only triggered by
changes in the controlled variable; appropriate selection of the parameters results in a
largely constant controlled variable x.
xd
-
w
+
-
3
2
x
-
Period T
-
System deviation xd
-
Parameters Kp, Tn, Tv
1
Control amplifier
2
Controlled system
3
Setpoint adjuster
4
Pulse/pause converter
Figure 1-11 a) Function diagram
Adjustment of the period (separately for heating/cooling) permits the controller to be
adapted to the special type of heater or the cooling unit. A compromise has to be made
beween the control quality and the degree of wear.
Short period:
Long period:
SIPART DR21
C73000-B7476-C143-08
1
4
-
y
z
b) Switching output and resosne of controlled variable
Improved control quality, but increased wear on contact/heating valve.
Prime use with electric heaters.
Low wear on contact/heating valve, but poorer control quality. Prime
application with gas heaters or coolers.
1 General Part -- Fundamental control technology terms
Duty factor 0 %
w
Duty factor
100 %
y
On
Off
*)
T
w
Command variable
x
Controlled variable
y
Manipulated variable
Z
Disturbance variable
T
Period
*)
2 ¢ 100 %
Kp
t
t
Duty factor (in % if period)
15
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