Interfaces to automation systems
8.1 PROFIBUS DP interface
SITRANS SL
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Operating Instructions, 12/2010, A5E01132948-04
To install the SITRANS SL as a device in-between other devices on a PROFIBUS segment:
1.
Ensure that the termination resistor is turned off.
2.
Connect the PROFIBUS hybrid cable to the SITRANS SL receiver.
3.
Use a junction box to connect supply voltage to the PROFIBUS hybrid cable.
4.
For connecting the SITRANS SL to the PROFIBUS segment there are two options:
–
Active bus tap-off: Use a bus terminal, repeater or an active cable to make the T-
connection. In an Ex environment the repeater used must either be certified for use in
an Ex environment, or be placed in a safe zone.
–
Passive bus tap-off (stub-wire): Connect the SITRANS SL directly to the PROFIBUS
segment.
Note
Note that the hybrid cable will become a stub-wire of the PROFIBUS segment.
This solution should only be considered by experienced PROFIBUS users, and if the
network segment is known to have good quality. According to the PROFIBUS
standard, the total length of stub-wires in a PROFIBUS segment must be less than
6.6 m at 1.5 Mbits/s provided that Type A cable is used. For higher bit-rates, stub-
wires shall not be used.
Reference Voltage
●
Grounded reference voltage system
This is the standard arrangement for PROFIBUS DP devices, where the shield of the
PROFIBUS cable is connected to protective earth (PE) at every device.
To achieve this in the SITRANS SL, connect screw terminal 15 (PROFIBUS shield) to
screw terminal 24 (Ground) in the SITRANS SL Receiver.
●
Non-Grounded reference voltage system
To achieve this in the SITRANS SL, ensure that screw terminal 15 (PROFIBUS shield) is
connected only to the shield of the PROFIBUS cable. Ensure that the shield of the
PROFIBUS cable is not connected to the chassis at the cable gland.
The SITRANS SL is equipped with a standard R/C circuit between PROFIBUS shield and
protective earth (PE) in order to improve interference immunity for non-grounded
reference voltage systems.