Macurco MRS-485, Инструкция пользователя

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Macurco DVP-120C Manual
REV – 1.0 [34-8708-4770-8 ] 14 | P a g e
Remote sensors must be connected at RS-485 connection labeled TB1 (Refer Figure 3-10). A Modbus over Serial Line
Cable should be shielded for best performance. The shield should be connected on each detector at SHD terminal
and connected to a ground terminal or chassis only at one end of the bus. An RS485-MODBUS must use a balanced
pair (for A-B) and a third wire (for the Common). For RS485-MODBUS, Wire Gauge must be chosen sufficiently wide
to permit the maximum length (1000 m or 3281ft). AWG 24 is always sufficient for the MODBUS Data. Category 5
cables may operate for RS485-MODBUS, to a maximum length of 600 m 1968.5 ft. For the balanced pairs used in an
RS485-system, wire with a characteristic impedance of higher than 100 Ohms may be preferred, especially for 19200
and higher baud rates.
Note
: It is recommended to always use twisted wires to reduce noise and allow for reliable data communication
over greater distances. Use at least 3-conductor wire with one twisted pair providing a pair for signal (A & B) and
common (COM) connections.
For best performance use shielded 3-conductor wire with one twisted pair providing a pair for signal (A & B),
common (COM) and shield ground (SHD) connections.
Figure 3-6 MRS-485 Wiring
3.2.3.1 Topology
An RS485-MODBUS configuration without repeater has one trunk cable, along which devices are connected, directly
(daisy chaining) or by short derivation cables. The trunk cable, also named “Bus”, can be long. Its two ends must be
connected on Line Terminations. (see Line Termination - End of Line Resistor section). The use of repeaters between
several RS485-MODBUS is also possible.
The DVP-120C has a single Modbus termination block that will accept two trunk cable connections allowing for two
MODBUS communication lines. The Trunk cable must be wired in parallel from the panel to the end of line with no
off shoots “T-tapping”.
3.2.3.2 Length
The end to end length of the trunk cable must be limited. The maximum length depends on the baud rate, the cable
(Gauge, Capacitance or Characteristic Impedance), the number of loads on the daisy chain, and the network
configuration (2-wire). For a maximum 9600 Baud Rate and AWG26 (or wider) gauge, the maximum length is 1000m
3281ft. The derivations must be short, never more than 20m 65.5ft. If a multi-port tap is used with n derivations,
each one must respect a maximum length of 40m 131ft divided by n.
3.2.3.3 Grounding
The Shield (SHD) must be connected directly to protective ground, preferably at one point only for the entire bus.