Chapter 5: Process Interface
56
Cable
It is recommended to use cables, which fulfil the EN 50170 type A:
Wave impedance [Ω]
135 … 165 at 3 ..20 MHz
Loop resistance [Ω/ km]
< 100
Core diameter > 0,64
Nom. Capacitance Conductor to Shield [pF/m] < 30
Table 3 Cable specification (EN50170)
The maximum fieldbus cable length per segment is dependent of the baud rate.
Baud rate Maximum length of segment
9,6; 19,2; 93,75 kBaud 1200 m
187,5 kBaud 1000 m
500 kBaud 400 m
1500 kBaud 200 m
3000 – 12000 kBaud 100 m
Table 4 Maximum segment length as a function of the baud rate
It is recommended to use a termination resistor, which are typically included in the fieldbus
connectors. The termination resistors provide low impedance that reduces the sensitivity to
electrical noise and prevents data reflection that can cause data communication corruption.
Figure 10 Termination resistor
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