PM 1000288 000 00
Device handbook SIRAX BT5100
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5.6 Modbus interface RS485
Via the optional Modbus interface measurement data may be provided for a superior system.
MASTER
+3.3 / +5V
Rx/Tx+,A
RS485 Bus
Rs
Rt
Rs
Rx/Tx-,B
G
1)
Rt
A B G
A B G
A B G
The signal wires (A, B) have to be twisted. G can be connected via a wire or via the cable screen. In disturbed environments shielded cables must
be used. To avoid the possibility of loop currents, an Earth connection should be made at one point on the bus. Supply resistors (Rs) have to be
present in bus master (PC) interface. Stubs should be avoided when connecting the devices. A pure daisy chain network is ideal.
You may connect up to 32 Modbus devices to the bus. A proper operation requires that all devices connected to the bus have equal
communication settings (baud rate, transmission format) and unique Modbus addresses.
The bus system is operated half duplex and may be extended to a maximum length of 1200 m without repeater.
5.5 Connection Diagram
1) One ground connection only. This is
possibly made within the master
(PC).
Rt: Termination resistors: 120 Ω each for
long cables (> approx. 10 m)
Rs: Bus supply resistors,
390 Ω each
Label version
Before commissioning you have to check if the connection data of the device
match the data of the plant.
If so, you can start to put the device into operation by switching on the power
supply and the measurement inputs.
6. Commissioning
Connection
5
6
I/P ~
I/P ~
AUX
7
8
1
2
3
4
Measuring input
Auxilliary power supply
Measuring output - 1
Measuring output - 2
Terminal details
~
+
AUX ~
-
O/P1
O/P1
+
-
O/P2
O/P2
+
-
–
–
–
A
B
G
Modbus
5
6
7
8
1
~
~
~
~
+
-
+
-
+
2
3 4
A B G
RS485
-
Input U
AUX
Output-1
Output-2
