HART Multiplexer System KFD*-HM*-16
Appendix
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9.4
Glossary
Address
In communications technology, the address of a device is used to identify that device, so that
messages can be delivered correctly. HART uses two forms of addressing: a polling address in the
range 0 to 15, and a unique identifier (long frame format address) of 38 bits. The polling address 0
is reserved for 4 mA ... 20 mA analog transmitters in
point-to-point networks, polling addresses
1 ... 15 for transmitters in
multidrop networks.
Broadcast Mode
Burst Mode
Burst Mode
A communication mode in which a Master device instructs Slave devices to continiously broadcast
process values (e. g. the
primary variable) until the Master instructs it to stop. The Multiplexer
recognizes and supports this mode, but itself does not instruct field devices to use this mode.
FSK
Abbreviation for
F
requency
S
hift
K
eying. Method of coding the two digital signals "0" and "1" with
two different frequencies.
HART
Abbreviation for
H
ighway
A
ddressable
R
emote
T
ransducer. Used to describe communications
that complies to the HART specification. HART is a
Master-Slave system.
Host
Higher layer system, e. g. service station, PC or process control system.
Long frame address
Address
Master
A device (e. g. the process control system) in a
Master-Slave system that initiates all
transactions and commands.
Master-Slave system
A communication system in which all message transactions and commands are always initiated by
a
Master device and
Slave devices only respond to requests received.
Multidrop
In contrast to
point-to-point, more than two (field) devices are connected together to one
segment (pair of wires) in a multidrop system. To correspond to each singe device it must have a
unique
address. Because communication can only be established to one field device, cycle
times are increasing proportional to the number of field devices. In HART multidrop operation the
current through each field device is fixed at 4 mA to allow parallel operation of more than one
device (up to 15 devices are possible).
Multimaster
HART allows connection of two Masters, a primary and a secondary Master. A high level station is
configured as primary Master, usually this is the process control system or the main service
station. A lower level station is configured as secondary Master, this may be a hand terminal or a
service station. The difference between primary and secondary Master is the priority of the bus
access: 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 recognize which responses are
intended for them.
Point-to-point
In a point-to-point communication system, only two communicating devices are connected
together to one segment (pair of wires). A point-to-point system is for example the Master-Slave
system Multiplexer-field device.
Primary Master
Multimaster
Primary variable
Process value measured by a field device. The unit depends on the used HART command (see
commands 1, 2 and 3). The primary variable of a pressure sensor could contain for example the
measured process pressure in the unit "bar".
Secondary Master
Multimaster
