Pepperl+Fuchs KFD HM 16 Series Manual page 23

HART Multiplexer System KFD*-HM*-16
Installation
Note
4.2.3 Cabling for the analog signals
4.2.4 Location of electrical connections
4.2.5 Note on electromagnetic compatibility (EMC)
In accordance with the RS 485 specification up to 32 stations ("multidrop") can be
connected to a up to 1200 m cable (for data rates less than 100 kBaud).
Pepperl+Fuchs recommends that this length of cable is not exceeded. Even though
problems seldom occur at these data rates, screened twisted two-wire cabling
should be used.
In addition a terminating resistor should be connected to each end of the RS 485
cable. If the Multiplexer Master is such a device, i. e. the RS 485 cable ends here and
is not routed to other devices, then the second available connection terminal for the
RS 485 can be used for the connection of a terminating resistance. The terminating
resistor terminates the cables with its characteristic impedance. At minimal baud
rates and with short lengths of cable, in practice quite often no terminating resistors
are used. If communication errors arise, or if these are to be positively excluded from
the outset, terminating resistors typically of 120  ... 220  should be used.
If an interface converter is used, a terminating resistor should be connected to the
converter and another to the other end of the cable.
The individual I/O components of the HART product family are connected by a single
26-pin system plug connector for the connection of the individual current repeaters
(for plug pin assignment see section 9.2).
Pepperl+Fuchs provide specially developed connector units (HART interfaces type
FI-***) for this purpose. As required, the connection to these units can be via a
system cable or even by means of conventional screw connections. If the current
repeaters are mounted on a motherboard (MB-***), the connection is made directly
from the board to the Multiplexer via a flat cable type K-HM26.
The control system is connected via a system specific connector of the motherboard
or the Flex-interface. Flex-interfaces with screw terminals are available for the
purpose of individual wiring.
The power supply (24 V DC nominal voltage) is provided via the Power Rail or
terminals 17 (+) and 18 (-). The device is protected against reverse polarity by
means of a protection diode.
The connection of a higher level control unit (PLC, PC) is achieved via an RS 485
interface on terminals 13, 14 and 15. The RS 485 bus is looped through to terminals
19, 20 and 21. In this way, the three terminals can be used alternatively, or
simultaneously, (for the connection of other devices with RS 485, or for the
connection of a terminating resistor). If a standard PC with an RS 232 interface is to
be used, an interface converter is required.
The connection of the KFDO-HMS-16 HART Multiplexer Slaves is via the 14 pin plug
connector on the side of the device.
The analog HART signals are connected to the current repeaters via the 26 pin plug
connector on the front of the device.
The device is intended for use in electrically conductive and earthed control
cabinets. Leads that are fed into the control cabinet should be screened and the
screen should be connected with the control cabinet at the point of entry, preferably
directly in the cable gland. Unscreened leads in the control cabinet (e. g. power
supply leads) should be fed via filters.
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