Rockwell-automation 1760-xxxx Pico GFX-70 Controllers User Manual Manual de usuario descargar pdf (Pagina 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

mmΩ/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’

1 2 ... 64 65 66 67 68 69 70 71 72 73 74 ... 399 400

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