MS/TP and Modbus RS485 Communications on StruxureWare Automation Server

Issue

Both BACnet MS/TP and Modbus typically provide a robust and reliable communications channel allowing the Automation Server to effectively manage a large collection of equipment over extended distances. When the system does not come up operating as expected due to the communications integrity, considerable effort can be consumed troubleshooting or working-around the fault observations.

Product Line

Andover Continuum, TAC I/A Series, Field Devices, SmartStruxure Solution, Other

Environment

Automation Server with BACnet MS/TP or Modbus RS485 networks connected to Port A or Port B.

Cause

The configuration of the RS485 network can create conditions that reduce the tolerance for EMI noise on the bus, electrical ground differences, transmission signal loss through the cable and/or component performance.

Resolution

A collection of application notes and Quick Start Best Practices Guides are available on the subject of BACnet MS/TP and Modbus RS485 network connections to the StruxureWare Automation Server.  These application notes and quick start guides provide recommendations in the areas of –

  • BACnet MS/TP & Modbus RS485 Network Termination
  • Network Biasing Options and Techniques
  • Unit Load and associated Maximum Node Count Recommendations
  • Isolated RS485 Interfaces and related Expanded Unit Load
  • Cable Specifications and Suggested Cable Selections
  • Cable Routing and Recommended Lengths

The documents describe configurations of cable, network length, node counts and bias arrangements providing compliance with the EIA/TIA-485 Standard and TSB-89-A Guidelines with the objective of optimizing system tolerance for noise, grounding and transceiver component variations.  Most of the application notes and quick start guides target specific product families which include the Andover Continuum b3 Family, TAC I/A Series MNB Family, Legrand Power Meters and the Viconics VT7000 series sensors. There is also an application note and quick guide directed toward other “Generic” RS485 MS/TP and Modbus devices where the user is guided through a sequence of information collection steps to determine the appropriate recommendations. 

The collection of application notes and guides are available on the Schneider Electric download center. The list of links below will take you to the applicable download page.

Note:    If using the download center for the first time, you will need to register. See Lessons Learned Article #15967 for more information. The Download Center requires the use of Internet Explorer (version 8 or higher), Google Chrome or Firefox browsers.

Additional information is available in the "1.4 Hardware Configuration Guide" and the "1.5 Hardware Configuration Guide",

To access the StruxureWare Building Operation Web Help, please click HERE

Also check out the SmartStruxure-RS485-Controller Unit Load Quick-Help video on the Exchange.