Tips for Correcting Bus Installation Problems - Metasys - LIT-12012443 - Software Application - MS-FIT100-0 Field Inspection Tool

MS-FIT100-0 Field Inspection Tool User Guide

Product name
MS-FIT100-0 Field Inspection Tool
Document type
User Guide
Document number
Revision date

The MS/TP Bus is subject to a number of installation factors that can affect performance. Consider the following common physical attributes when trying to resolve communication problems:

  • Validate controller/device power is available and undisrupted.
  • Check wiring for:
    • - Proper wire gauge, cable type, connections, polarity, and lengths.
    • - Opens and shorts.
    • - Confirmation that one shield ground point exists per bus segment (made at the source of the bus segment —the NAE, Side B of a Repeater).
  • Check EOLs to verify that EOL terminations are only at the ends of daisy chains for each bus segment.
  • Check addresses for:
    • - duplicate addresses
    • - address ranges are sequential
  • Check for and eliminate T-Taps (wire configurations that create a T shape) and star configurations.
  • Check for consistent baud rates (often baud rates problems occur with vendor devices and repeaters).
  • Check for sources of electrical interference.

Here are some additional best practices to find and eliminate problems with the physical layer:

  • Check and confirm proper idle voltage levels on each bus segment. See Voltage Menu and Voltage Levels for more information.
  • Separate the bus into smaller segments to isolate and find problems.
  • Check idle voltage levels on these smaller segments.
  • Use the FIT’s 1-ON-1 modes on disconnected controllers to validate they have proper attributes and are not defective. See 1-ON-1 Menu for more information.
  • Remove vendor equipment from the bus. Johnson Controls does not manage vendor equipment communication or default states. Isolating a bus to devices with known defaults ensures effective communication.

See Getting Prepared to use the FIT section for ways to use the tool on unpowered buses to validate continuous bus wiring and end-to-end continuity.