Aalborg DPC, Руководство по эксплуатации

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NOTE: Address 00 is reserved for global addressing. Do not assign the global
address to any device. When a command with the global address is sent, all
devices on the RS-485 bus execute the command but do not reply with an
acknowledgement
message.
Do not assign the same RS-485 address for two or more devices on the same
RS-485 bus. If two or more devices with the same address are connected to one
RS-485 network, a communication collision will take place on the bus, causing
communication
errors to occur.

d) RS-485 Termination (applicable to RS-485 only)
A refl ection in a transmission line is the result of an impendance discontinuity that a
traveling wave sees as it propagates down the line. To minimize such refl ections from
the ends of the RS-485 cable, the user must place a Line Termination (LT) near each of
the two ends of the RS-485 bus. If you are connecting a DPC controller as the last
device in the end of a long (more than 100 meters) transmission line, you can use
this menu selection to internally connect a 120

resistor between the RS-485 + and
– wires.
NOTE: Do not Enable Termination if the transceiver is set to RS-232 mode. Doing
so will cause damage to the instrument or improper operation of the
communication interface. The factory default setting is Disabled.

6.4.15.5 Submenu “Modbus Interface” (optional)
If the DPC fl ow controller is equipped with Modbus interface, this menu selection allows the
user to change the Modbus device ID (address) and its communication parameters.
Modbus is a standard protocol developed by A.E.G. Schnieder. The DPC supports only the
Modbus RTU version. Modbus RTU enable a computer or a PLC to read and write directly
to registers containing the instrument's parameters (see technical document TD-DPMC-
MOD-0118
“Modbus RTU slave interface for AALBORG digital mass fl ow instruments” for
a detailed description of supported Modbus functions and registers).
The following parameters are available for “Modbus Settings” (see Figure 19 ):
a) Device ID (Address) (Numerical entry)
Decimal representation ranges from 1 to 247. By default, all DPC controllers are
equipped with a Modbus interface shipped from the factory with the Device ID
parameter set to decimal 11.
NOTE: Do not assign the same ID address for two or more devices on the same
Modbus segment. If two or more devices with the same address are connected
to the one Modbus network, a communication collision will take place on the
bus,
resulting in communication errors.
