Moniteur 50 Series SMART Positioners - Manual (Page 16)

Introduction
1-6
Positioner SIPART PS2/SIPART PS2 PA
C79000-G7476-C150–01
The maximum number of devices that you can connect to a bus train
depends on the current consumption and the application conditions.
During operation in a safe zone, the couplers or links supply up to 400
mA to the bus.
In zones subject to explosion hazard, intrinsic safety is only ensured if
the maximum power fed into the bus does not exceed certain voltage
and current values.
These are usually:
EEx ia IIC
Current I
S
< 128 mA, voltage U
0
<15V
!
Warning
To power the intrinsically safe PROFIBUS only certified power supply
units (DP/PA couplers or links) must be used. See the Ex conformity
declaration for the requirements (see Assembly and Installation
Instructions).
From the sum of the maximum current consumption of the connected
devices (acc. to standard = 10 mA per device) and the available cur-
rent, it is possible to calculate the number of devices that can be con-
nected to a bus train. For safety reasons, a current reserve must be
planned because otherwise there is a risk that a defective device could
overload the bus by increased current consumption and that therefore
the power supply and communication with all the other non–defective
stations could collapse. The size of the required reserve depends on
the current increase in case of fault stated by the device manufacturer.
The electronic current limitation additionally installed in the SIPART
PS2 with PROFIBUS PA ensures a maximum increase of the current
consumption by 3 mA for a defective device.
In order to distinguish the connected process devices from one
another, each device has its own address. The address setting is de-
scribed in Section 3.6 ”Commissioning”.
For more detailed information about the components, assembly guide-
lines and configuration, see the technical description of the field
technology package /2/.