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Profibus-PA
(Process Automation) uses synchronous transfer mode technology, as defined in
IEC 61158-2 standards, to communicate between field devices and the
RS 485
backbone of Profibus-DP. A
Segment Coupler
,
or gateway is installed to bridge Profibus-DP with Profibus-PA. Otherwise, the
protocols are identical, allowing transparent communication between general
purpose automation systems and decentralized field devices. Profibus-PA is a
master-slave bus. Transmitters used in the process industry are typically slave
devices or passive stations which only communicate at the request of the master.
Profibus-PA operates on the voltage mode with a transmission
speed of 31.25 kBit/s. In this way the data packages are modulated onto the
supply voltage for the fieldbus station and transmitted via a special shielded
two-wire cable. The bus physics offer fieldbus communication and power supply of
the bus station using a single cable.
A
Segment Coupler with an intrinsically-safe output is necessary for use in
explosion-hazardous areas. This, however, reduces the output power and the
number of connectable bus stations. This situation can be remedied by a topology
which is based on the use of EExe (increased safety) main line (trunk line) and
intrinsically safe outputs. This is where the
Multibarrier is employed, permitting a current of up to 10 A in the
trunk line area, and when connected in series, supplying up to 32 intrinsically
safe stations in the hazardous area.
More about Profibus from the Profibus website. |
