Configuration example of an electrical RS 485 network with linear/tree structure

The network size with an electrical RS 485 network is in total smaller than that with an optical network. However, by using segmenting and signal regeneration with up to 9 repeaters, distances from 1 km (at 12 Mbps) up to 10 km (at 187.5 kbit/s) can be achieved depending on the transmission rate.

A segment can have up to 32 participants (master/slaves), and the total network up to 126 participants. The start and end of each segment must be terminated by an active bus resistor which is typically pre-integrated in the device (e.g. repeater) or is available as an active RS 485 termination element.

The configuration example (figure at top right) shows a typical addressing scheme for a PROFIBUS DP network made up of multiple segments. Although repeaters are electrical participants on the PROFIBUS, they are not assigned a slave address since they are not directly addressed by the master.

FastConnect

FastConnect Stripping Tool

PROFIBUS FastConnect is a system for fast and easy assembly of PROFIBUS copper cables. The system comprises compatible components:

• FastConnect Standard Cable for fast assembly
• FastConnect Stripping Tool
  with FastConnect Blade Cassettes (spare blade cassettes for the stripping tool)
• FastConnect bus connector for PROFIBUS

Repeater for PROFIBUS

A repeater links the individual bus segments with RS 485 technology. Main applications are:

• Increase in number of nodes and distances
• Electrical isolation of segments

If diagnostics functions for physical cable diagnostics are desired in addition to the standard repeater functionality, a diagnostic repeater can be alternatively used. It monitors the copper bus cables in online mode. In the event of a fault it sends a diagnostic message with detailed information about the type and location of the fault to the DP master.

Active RS 485 terminating element

The active RS 485 terminating element is used to terminate bus segments. The component supplied with 24 V DC independent of the bus nodes provides a defined RS 485 signal level, and suppresses reflections on the line. Bus nodes (e.g. ET 200S) can be coupled and decoupled without feedback to/from PROFIBUS networks terminated by active RS 485 terminating elements.

RS 485-iS coupler

The RS 485-iS coupler is an isolating transformer with which the PROFIBUS DP fieldbus can be routed intrinsically-safe into the hazardous area.

The RS 485-iS coupler has the following functions:

• Connection of intrinsically-safe PROFIBUS DP stations, e.g. ET 200iSP or devices from other vendors with Ex i DP connection
• Conversion of the electrical PROFIBUS DP RS 485 transmission technology into the intrinsically-safe RS 485‑iS transmission technology with a transmission rate of 1.5 Mbps
• Suitable as a safety barrier
• Additional use as a repeater in the hazardous area.

The RS 485‑iS coupler as an open resource can only be used in housings, cabinets or rooms for electrical equipment. It is assembled on a SIMATIC S7‑300 rail which can be positioned horizontally or vertically.

The RS 485‑iS coupler is integrated into the PROFIBUS as follows:

• Connection to standard PROFIBUS DP via standard Sub‑D socket (at the bottom on the RS 485‑iS coupler, behind the right front door).
• Connection of PROFIBUS DP with RS 485‑iS transmission technology via screw terminals (at the top of the RS 485‑iS coupler, behind the right front door)
• The last bus node on the intrinsically-safe PROFIBUS DP segment (not further RS 485‑iS couplers) must be terminated by a selectable terminating resistor using the connector, order no. 6ES7972-0DA60-0XA0.