CLIVET WSAN-EE 21 - Page 24

M02R40C8-00 29/07/08 page 24
12. UNIT INTERFACE VIA RS 485
Below the indications for the serial connection ; refer anyway to the CLIVET “RS 485 NETWORKS –
GUIDELINES” document and ask for the COMMUNICATION PROTOCOL about the COMPACT electronics
- The total length of each single serial line,
don’t have to be over 1000 metres
- The potential difference between the “ground”
of two RS485 switches must be less of 7 V
- Couple of conductors twisted and shielded
- Section of conductor 0.22mm
2
…0,35mm
2
- Nominal capacity between conductors < 50
pF/m nominal impedance 120 Ω
- Recommended cable BELDEN 3105 A
TYPE OF NETWORK
The serial lines must be connected in bus typology, i.e. nodes to more points are not admitted
OK
NO !
SHIELD
It must be connected to a ground without disturbances
Connected to round in only one point
Provide to the shield continuity during all the serial
cable extension.
Sistema di supervisione
232
485
_
+
GND
_
+
GND
RS 232
L. max 10 Mt
RS 485
L. max 1000 Mt
_
+
GND