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HART Multiplexer System KFD*-HM*-16
Appendix
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8-04
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FDT
The FDT concept (FDT
–
F ield D evice T ool) created a standard that can be used to integrate
devices in various user interfaces (framework applications such as PACTware ).
The FDT concept enables open and continuous device operation from the control level to the ,
regardless of the bus systems used. The FDT concept specifies the data exchange between
the device-specific driver and the framework application. Every communicating device has a
device-specific driver (DTM) that is integrated in the framework application.
FSK
Abbreviation for F requency S hift K eying. Method of encoding the digital information 0 or 1 with
two different frequencies.
HART
Abbreviation for H ighway A ddressable R emote T ransducer. Designation for communication
according to the HART protocol. HART is a master-slave system.
Host
Higher-level system, e. g., maintenance station, computer, or process control system.
Polling address
See Address
Master
A device
–
e. g., the control system
–
in a master-slave system which initiates all
transmission requests and commands.
Master-slave system
Communication system in which a master initiates all transmission requests and commands
and a slave responds to the transmission requests and commands.
Multidrop
In contrast to point-to-point connections, several (field) devices may be connected to one
segment (core pair). To allow each device to be addressed individually, the device must have
a unique address. As communication can only take place with one field device at a time,
cycle times increase in proportion to the number of field devices. In HART multidrop operation,
field devices fix their current consumption at 4 mA to enable parallel operation of up to
15 devices.
Multi master
HART allows the connection of two masters, a primary master and a secondary master. The
main station is configured as the primary master
–
this is generally the control system or the
main control. A second station is configured as secondary master
–
this can be a handheld or a
maintenance station. The difference between the primary and secondary masters is the priority
of access, i. e., the primary master has a higher priority than the secondary master. Messages
sent by the masters are characterized by a master bit so that the masters can assign the
message responses to their own messages.