Before we
look at Foundation Fieldbus (FF) and Profibus let’s find out why digital signals are
commonly used in industrial data transmission.
Foundation Fieldbus and Profibus
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Digital
signals can be transmitted without loss of integrity, via a hardwired parallel
or serial bus, radio transmitter or fiber optics.
Digital data
transmission speeds are higher than with analog data transmission.
Digital
signals can be transmitted without loss of accuracy and can contain codes for
limited automatic error correction or for automatic requests of data
retransmission.
Digital
transmitters consume less power as compared to analog transmission devices
hence they are preferred for use in industrial communication systems over
analog devices.
Foundation Fieldbus and Profibus
The
Foundation Fieldbus (FF) and Profibus are the two most universal serial data
bus formats that have been developed for interfacing between central processor
and smart sensing devices in a process control system.
The FF is
primarily used in the USA and the Profibus is primarily used in Europe.
Process
control equipment is presently manufactured to accept either of these formats.
A serial
data bus is a single pair of twisted copper wires, which enables communication
between a central processing computer and many monitoring points and actuators
when Smart Sensors are used.
Although
initially more expensive than direct lead connections, the advantages of the
serial bus include: Minimal bus cost and installation labour. The system
replaces the leads to all the monitoring points by one pair of leads. New units
can be added to the bus with no extra wiring i.e. plug and play feature, giving
faster control. Programming is also the same for all the systems.
The accuracies
achieved are higher than from using analog, and more powerful diagnostics are available.
The bus
system uses time division multiplexing, in which the serial data word from the
central processor contains the address of the peripheral unit being addressed
in a given time slot, and the data being sent.
In the FF,
current from a constant current supply is digitally modulated. Information on
the FF is given in the ISA 50.02 standards.
One drawback
of the FF is that a failure of the bus, such as a broken wire, can shut down
the entire process, where with the direct connection method, only one sensor is
disabled. This disadvantage can be overcome by the use of a redundant or backup
bus in parallel to the first bus, so that if one bus malfunctions, then the
backup bus can be used
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Good explaination
ReplyDeleteWelcome.
DeleteExcellent explanation, but I thought that it was a Profibus description as well. You should definitely add information about it.
ReplyDeleteHi Emilio, thanks for reading! I didn't cover much on Profibus, because it is almost similar to Foundation Fieldbus. If you understand FF, then you won't have difficult time getting to know Profibus.
DeleteControl in Field in Foundation Fieldbus will meet the Requirement of single cable
ReplyDelete