Bronkhorst PROFIBUS-DP slave interface Instrukcja Użytkownika Pobierz pdf (Strona 10)

BRONKHORST®

2.5 SPUR LINES WITH PROFIBUS DP

(Also known as stubs or branches)

In table 5 the maximum spur capacitance is set out to the baud rate.

With the use of PROFIBUS cable type A this will result in the stated length.

Transmission rate

(kbit/s)

Total allowable spur capacitance

(nF)

Total Spur cable length* (ΣL

)

(m)

19.2

500

93.75

3.0

100

187.5

1.0

500

0.6

1500

0.2

6.7

> 1500

none

None

* Calculated for PROFIBUS cable type A at 30 pF/m

• The maximal Spur line length is 0.25m

• The total Spur line length of a segment represents the sum of all Spurs attached to that segment.

• The minimal Trunk line length should be longer then the sum of all Spur lines

• Spurs on DP segments should be avoided where possible.

• Each PROFIBUS device will have a short Spur line carrying the bus signals between the external bus

connector and it’s RS 485 driver chip (for calculations use about 5cm per node).

• Devices are tested for reflections as part of the certification process.

• Uncertified devices can cause reflections.

Example:

We are installing a M12 system with 19 nodes and a spur length of 25 cm.

Additional 30 Sub-D instruments are installed.

Transmission rate at 1500 kbits/s.

Is this allowed?

(19 nodes x 25cm + 19 nodes x 5cm) + 32 nodes x 5cm = 7.3m

The maximum spur length at 1500 kbits/s is 6.7m so this is not allowed.

When spur lines are installed, additional termination at the end of a spur-line should not be used!

The rule that we must never exceed two terminations per segment, still applies even if using spurs.

References:

http://PROFIBUScentre.com.au/docs/DP_Spur_Lines.pdf

Spur-lines are not allowed when using higher baud rates (>1.5Mbit/s).

At baud rates lower than 1.5Mbit/s, spur-lines are allowed up to the maximum capacitance for the

baud rate.

Page 10 PROFIBUS DP interface 9.17.025

1 2 ... 5 6 7 8 9 10 11 12 13 14 15 ... 24 25

Komentarze do niniejszej Instrukcji

Brak uwag

Bronkhorst PROFIBUS-DP slave interface Instrukcja Użytkownika Strona 10

Komentarze do niniejszej Instrukcji

Powiązane produkty i podręczniki dla Oprogramowanie Bronkhorst PROFIBUS-DP slave interface