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266CRH / 266CRT, 266CSH / 266CST MULTIVARIABLE PRESSURE TRANSMITTER | OI/266CXX/MODBUS-EN REV. A
... 6 Installation
... Electrical connections
Cable specification
The maximum permissible length depends on the baud rate, the
cable (diameter, capacity and surge impedance), the number of
loads in the device chain, and the network configuration (2-core
or 4-core).
•
At a baud rate of 9600 and with a conductor cross section of
2
at least 0.14 mm
(AWG 26), the maximum length is 1000 m
(3280 ft).
•
If a 4-core cable is used in a 2-wire system, the maximum
length must be halved.
•
The spur lines must be short (maximum of 20 m [66 ft]).
•
When using a distributor with 'n' connections, the maximum
length of each branch is calculated as follows:
40 m (131 ft) divided by 'n'.
Change from two to one column
The maximum cable length depends on the type of cable used.
The following standard values apply:
•
Up to 6 m (20 ft): cable with standard shielding or
twisted-pair cable.
•
Up to 300 m (984 ft): double twisted-pair cable with
overall foil shielding and integrated earth cable.
•
Up to 1200 m (3937 ft): double twisted-pair cable with
individual foil shielding and integrated earth cables.
Example: Belden 9729 or equivalent cable.
A category 5 cable can be used for Modbus RS485 up to a
maximum length of 600 m (1968 ft). For the symmetrical pairs in
RS485 systems, a surge impedance of more than 100
preferred, especially at a baud rate of 19200 and above.
is
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