Siemens SIPART DR21

1 General Part -- Fundamental control technology terms Manual
14
SIPART DR21
C73000-B7476-C143-08
D Two-position controller
The two-position controller (or three-position controller for heating/cooling) is used to activate
relays, contactors or thyristor switches for electric heating or cooling.
- Two-position controller without feedback
In the simplest version without feedback, two-position controllers operate an on/off
switch. The controllers output is switched if the controlled variable violates the upper or
lower limits of the switching hysteresis (x1 and x2). The controlled variable x is subject to
permanent oscillation whose frequency and amplitude depend on the delay time of the
system and the switching hysteresis of the controller.
1 Controller
2 Controlled system
3 Setpoint adjuster
3
w
xd
1
y
2
x
z
t
t
x
y
x1
x2
w Command variable
x Controlled variable
y Manipulated variable ON/OFF
z Disturbance variable
On
Off
Figure 1-10 a) Function diagram b) Switching ouptupt and response of controlled variable