4.6.7 TERMINAL 26-31: TYPE CB / CH / CI - COMMUNICATION (OPTION)
Serial communications on hardware layers RS232, RS485 and TTL (intrinsic safety) are possible.
Make sure that the hardware layer specific requirements are met to achieve reliable communication
and read the Modbus communication protocol and Appendix C.
It is advised to use shielded cable with twisted wire pairs, to prevent EMC disturbance. Connect the
shield only on the side of the Modbus master device to prevent ground currents and voltage lifts.
Fig. 29: Terminal connections - Communication (typical)
When using RS485 communication, the polarity of the letters is sometimes revered.
If all the communications setting, such as baud rate and address, are configured properly but
communicating is not working, try swapping the data wires. Reversing the wires will not
damage the device.
Type CB
An RS232 communications port for Modbus communication is available with this option. See above
figure for terminal connections; maximum cable length: 15 meters.
When using the RS232 communication option, terminal 27 is used for supplying the interface.
Please connect the DTR (or the RTS) signal of the interface to this terminal and set it active (+12V).
If no active signal is available it is possible to connect a separate supply between terminals
26 and 27 with a voltage between 8V and 24V.
Type CH
An RS485 2-wire communications port for Modbus communication is available with this option.
See above figure for terminal connections; maximum cable length: 1200 meters.
The interface is designed to operate without terminating resistors and its reliability is reduced
significantly if installed anyway. The interface can also be used when battery powered (type PB) but
battery life can be significantly reduced by high amounts of communication messages on the bus.
Please connect the non-inverting signal (D+) to line A and the inverting signal (D) line B.
Type CI
An RS485 4-wire communications port for Modbus communication is available with this option. See
above figure for terminal connections; maximum cable length: 1200 meters.
The interface is designed to operate without terminating resistors and its reliability is reduced
significantly if installed anyway. The interface can also be used when battery powered (type PB) but
battery life can be significantly reduced by high amounts of communication messages on the bus.
Please connect the non-inverting transmit signal (R+) to line A, the inverting transmit signal (R) to
line B, the non-inverting receive signal (T+) to line Y and the inverting receive signal (T) to line Z.
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