Rockwell Automation 1760-xxxx Pico GFX-70 Controllers User Manual - Manual (Page 69)

Publication 1760-UM002B-EN-P - March 2005
Installation 2-35
Cable Length and Cross-Sections
For correct operation of the network, the cable lengths, cross-sections and
cable resistances must correspond to the following table.
The surge impedance of the cables used must be 120 Ω .
Calculating the Cable Length with Known Cable Resistance
If the resistance of the cable per unit of length is known (resistance per unit
length R’ in
Ω /m), the entire cable resistance R
L
must not exceed the following
values. R
L
depends on the selected baud rates:
l
max
= maximum cable length in m
R
L
= Total cable resistance in
Ω
R’ = Cable resistance per unit length in
Ω
/m
Table 2.43
Cable length Cable Resistance Cross-section
m m Ω/m
mm 2 AWG
up to 40
≤ 140
0.13 26
up to 175 ≤ 70 0.25 to 0.34 23, 22
up to 250
≤ 60
0.34 to 0.5 22, 21, 20
up to 400
≤ 40
0.5 to 0.6 20, 19
up to 600
≤ 26
0.75 to 0.8 18
up to 1000 ≤ 16 1.5 16
Baud rate Cable resistance R
L
kBaud
Ω
10 to 125 ≤ 30
250
≤ 25
500
1000
≤ 12
l
max
= R
L
R’