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Instruction Manual
!
The number of devices which can be connected to a bus line is given by the total of maximum current
consumptions of the connected devices (³ 10 mA per device is the standard). A current reserve should be
planned for safety, otherwise there is a risk that a defective device overloads the bus with its increased
current consumption and the power supply and communication with all unaffected users could collapse.
The power reserve quantity depends on the current increase in the event of an error specified by the
manufacturer.
The electronic current limiter installed additionally in the SITRANS F/PA ensures that the current does not
increase by more than 5 mA even when a device is defective.
Every device has its own address to distinguish between the connected process devices. The address
setting is described in the chapter 3 "Commissioning".
See the System Description Field Technology /2/ for further information about components, setup
regulations and planning.
1.2
Function of the Device
The PROFIBUS PA variant of the SITRANS F differs from the 4 to 20 mA/HART version in the bus
interface and the omission of the digital output 2. This means that the basic functions of the device
including the operation and display remain basically the same. Function blocks 1 to 6 take care of the
interface tasks to the bus.
μP
+
Bus
controller
1
2
Figure 1--3 Block diagram of the bus link
1 The microprocessor interprets the bus command, initiates device-internal actions and provides
measured values, status and device data on the bus.
2 The device internal electronics are isolated from PROFIBUS PA by the potential isolator.
3 The bus interface contains the transmit and receive circuits for the bus system.
4 The electronic current limiter ensures that no illegally high current flows in the event of an error. This
avoids bus overloading, data communication with the other, unaffected users is maintained.
5 The reverse polarity protection enables the bus cables to be connected at any terminals and makes
installation errors almost impossible.
6 An EMC filter prevents malfunctions in the case of electromagnetic interference.
6
Warning
Only certified supply units (DP/PA couplers or DP/PA links) may be used to feed
the intrinsically safe PROFIBUS. See the EC Type Examination Certificate for
requirements.
3
4
Bus connection
5
6
SITRANS F with PROFIBUS PA
C79000-B5676-C114-03
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