EasyManuals Logo

Siemens SIPART DR21 User Manual

Siemens SIPART DR21
242 pages
To Next Page IconTo Next Page
To Next Page IconTo Next Page
To Previous Page IconTo Previous Page
To Previous Page IconTo Previous Page
Page #9 background imageLoading...
Page #9 background image
1HL1Manual
SIPART DR21
C73000-B7476-C143-08
9
1 General Part -- Fundamental control technology terms
D Control loop
The function of a closed-loop control is to bring the output variable x of a controlled system
to a predefined value and to retain this value even under the influence of disturbance
variables z. The controlled variable x is compared with the command variable w. The
resulting system deviation xd = w -- x is processed in the controller to the manipulated
variable y which acts on the controlled system.
The controlled variable x is measured cyclically in a digital control.
w Command variable
x Controlled variable
xd System deviation
y Manipulated variable
z Disturbance variable
1 Controlled system
2 Control equipment
z1 z2 z3
1
2
y
x
xd
w
-
+
Figure 1-1 Function diagram of control loop
D Sensors and transmitters
The controlled variable can be any physical variable. Frequently controlled variables in pro-
cess engineering are pressure, temperature, level and flow.
In most process engineering applications, the process variables are measured using sensors
and transmitters with a standardized signal output (0 to 20 mA or 4 to 20 mA). The standard-
ized signal can be connected to several process process devices (loop between e.g. re-
corder/indicator/controller). Temperature sensors such as resistance thermometers or ther-
mocouples, as well as resistance transmitters, can be connected directly to the controller
using appropriate input cards (options).
D Final control elements and actuators
In process engineering applications, the manipulated variale y primarily acts on the con-
trolled system via a valve, a butterfly valve or another mechanical means of adjustment.
Three types of drive are possible for actuating such final control elements:
- Pneumatic actuators with compressed air as the auxiliary energy and electropneumatic
signal converters or electropneumatic positioners. These have a proportional action and
are driven by continuous controllers.
- Electric actuators, consisting of an electric motor and gear unit. These have an integral
action and are driven by three-position step controllers. Electric actuators are also poss-
ible with an integrated (series-connected) positioner and then have a proportional action
and can be driven by continuous controllers.

Table of Contents

Questions and Answers:

Question and Answer IconNeed help?

Do you have a question about the Siemens SIPART DR21 and is the answer not in the manual?

Siemens SIPART DR21 Specifications

General IconGeneral
BrandSiemens
ModelSIPART DR21
CategoryController
LanguageEnglish

Related product manuals