Properties Of The Profibus Pa - Siemens PROFIBUS PA SIPART PS2 Manual

Introduction
(class 1)
(Field devices, decentralized peripherals,
secondary controls, mains transfer to PROFIBUS-PA)
Figure 1-5 Typical PROFIBUS automation system

1.2.3 Properties of the PROFIBUS PA

18
Master
PROFIBUS-DP
Slaves
Figure 1-5 shows the section of a typical PROFIBUS automation sys-
tem. The control system consists of two masters with distributed tasks.
The class 1 master looks after the control and regulation functions,
while the class 2 master enables operating and monitoring functions. A
cyclic exchange of measuring and setting data takes place between
master 1 and the field devices. Parallel to this data, the status data of
the field devices is transmitted to and evaluated in the class 1master.
No field device parameters are set or other device information read
during cyclic operation.
The information necessary for establishing communication is available
to the control system from the stored, device-specific device master
data (GS*) files (available on the Internet at
http://www.ad.siemens.de/csi_e/gsd).
One or more class 2 masters can access the field devices acyclically in
addition to the cyclic mode. With this communication type further infor-
mation can be fetched from the devices or settings made in the de-
vices.
The PROFIBUS PA enables bi-directional communication between a
bus master and the field devices via a shielded two-wire line. At the
same time the power is supplied to the two-wire field devices on the
same lines.
Master
(class 2)
8
x
PROFIBUS PA
I
SIPART PS2 PA Manual
A5E00127926-03