TESTO 6681 Profibus Instruction Manual page 44

testo 6681 Profibus
44
1.3.4.1 Data transfer and baud rate
With the RS485 transmission technology, the use of shielded and twisted
two-wire line of cable type A is recommended in accordance with EN 50170:
Loop resistance < 110 Ω/km
Surge impedance 135 to 165 Ω (at f= 3 to 20 MHz)
Wire diameter > 0.64 mm
Wire cross-section > 0.34 sq. mm
Effective capacitance < 30 pF/m.
Line lengths
The line length depends on the baud rate (see table).
Baud rate in kBit/s
Line length in m
(cable type A)
Bus cycle time
The bus cycle time is dependent on the
number of bus subscribers and the
selected transfer rate (see Fig.).
- 1.3 Commissioning
Depending on the transfer rate and number of repeaters,
distances up to 10 km can be achieved using this
transmission technology.
9.6
1200 1200
19.2 93.75 187.5
1200 1000
Bus cycle time (ms)
500 1500 12000
400 200
Subscribers
100