Installation
7300A user Manual
2-14
2.6. COMMUNICATION BUS CONNECTION
2.6.1. Polarity
By convention, the voltage on line ‘A’ of the bus, is higher than the voltage on line ‘B’ of
the bus, when the RS485 line is active.
2.6.2. Wires screening
To guarantee reliable operation of the digital communication link, the bus must be
connected using shielded twisted pairs.
Important !
• The shield of the communication cable must be connected to ground using the shortest
possible connection at both ends.
• We recommend connecting the shieleding to the DIN mounting rails as near as possible to
the interface.
2.6.3. Termination resistors
The communication bus must have termination resistors fitted at each end :
• One line impedance matching resistor
• Two RS485 bus polarisation resistors
The intertface as standard with the following internal resistors :
• 100 k
Ω
polarisation resistors,
• a 100 k
Ω
resistor betweeen the 'A' and 'B' terminals
Important !
• To ensure correct operation, we recommend installing a matchig resistor typical
value 220
Ω
, on the last unit on the communication bus
• If the last unit on the bus is one of the 7000S series with digital communication,
this resistor must be connected between terminals ‘A’ and ‘B
2.6.4. POWER SUPPLY CONNECTION ‘AUX2’
The digital communication option auxiliary power supply is 24 Vac or 24 Vdc
The typical power consumption is 1.5 VA.
A 2 Amps slow blow fuse is required to protect the connection leads.
ALR
1
a 1b
73 74
LDC
0VL LD
11 12
Aux2
24V 0VS GND
19 20 29
COM
B A
91 92
COM
B A
91 92
Aux2
24V 0VS GND
19 20 29
Digital
Communication
connector
Supply
connector
(24 Vac or
24 Vdc not
polarised)
2A
+
Figure 2.-16 Power supply connection diagram
