Spirax Sarco BC3250, Инструкция по установке и обслуживанию

Страница: 34 / 76

IM-P403-89 EMM Issue 8 34
5.11 EIA / TIA-485 communication wiring diagram
The product can be connected as a slave to a two or four-wire EIA / TIA-485 multi-drop network.
A
B
A'
B'
Fig. 26 RS485 / Modbus full duplex circuit (view from the top)
EIA / TIA-485 wiring notes:
EIA / TIA - 485 symbols are used (A = Tx - , B = Tx+ and A' = Rx - , B' = Rx+)
The signal direction is relative to the product being the Modbus slave, i.e. Tx+ from the product
(slave) is to be connected to the Rx+ of the master.
-
Twisted pair cable should not be required for short lengths of cable < 1.5 m (< 5 ft).
Standard screened cable should suffice.
-
The H / D (Half duplex) pins are used to select two or four-wire Modbus:
i) For two-wire mode, connect terminal 91 and 90 together.
ii) For four-wire mode, do not connect terminals 91 and 90 together.
Continued on page 35
Rx
Tx
Master
Common
Earth
*
R
*
R
*
*
See wiring notes
Fr
ont
Slave(s)
(Boiler controller)
-
Remove link between terminals 91 and 90.
90 91 92 93 94 95 96 97 98
H / D H / D Rx+ Rx
-
Tx+ Tx
-
SCN COM
R
*
R
*