profibus

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Profibus PA
Most modern devices, such as Endress + Hauser, offer Profibus PA reverse-connect protection. Where the A and B wires are crossed over at the device, the reversing of these polarities on the incoming and outgoing cable would not be detectable from the end of the cable or from the segment coupler, without physically opening up the instrument to verify the correct connection. Possible measurements using an external multi-meter are Voltage at the device (typically not less than 11V), connection between signal lines and cable shield, whether you have exceeded cable capacity etc.

Profibus DP.
Physical transmission via RS-485 has “NO” reverse-connect protection.
The two wires in the twisted-pair cable carry the “Data line plus” (B-line) and “Data line minus”(A-line) signals. The two wires in the PROFIBUS cable usually come colour coded. Normally red and green are used, however other colours may be found. When red and green wires are being used the following recommendations apply:
Red – B-line (RxD/TxD-P) (Aide-memoir: “B to RED” – “BREAD”)
Green – A-line (RxD/TxD-N)
On the Profibus DP side of the network, Pin allocations for Sub-D PROFIBUS connectors are Pin No. 3 RxD/TxD-P Data line plus (B-line) and Pin No. 8 RxD/TxD-N Data line minus (A-line). Pin allocations for M12 connectors are Pin No. 2 RxD/TxD-N Data line minus (A-line) and Pin No. 4 RxD/TxD-P Data line plus (B-line).
When 9-pin sub-D connectors or M12 connectors are used, the wiring must comply with that set down in the standard. Note that the cable shield should always be connected on every device.

Hope you find this information useful.