Appendix: optimizing SA Bus traffic - Metasys - LIT-12011034 - General System Information - Metasys System - Release 11.0

MS/TP Communications Bus Technical Bulletin

Product name
Metasys System
Document type
Technical Bulletin
Document number
Release 11.0
Revision date

This appendix describes how to configure the devices on the Sensor Actuator (SA) bus if excessive traffic on the bus is causing delays in communication.

Apply the solutions if:

  • Control applications on your site include multiple IOMs/XPMs that use more than 8 analog outputs (AOs) with fast control processes (time constant of less than 100 seconds)
  • The SA bus has more than 4 IOM471x devices

You can also apply these solutions if:

  • Analog input (AI) values on the SA bus report offline for a few seconds at a time. The IOM/XPM to which the AIs are connected may not show offline at the same time.
  • IOMs/XPM s on the SA bus report offline for several seconds during startup or shutdown of processes involving multiple AO commands.
  • Metasys Equipment Controllers experience unusually high CPU usage.

The solution to this problem is to limit the fast, sensitive control processes that occur over the SA bus. Examples of this type of control include airflow, static pressure control, and room pressurization. Instead, leave these control systems on the Metasys Equipment Controller or engine itself, and move slower response or monitor only points on the SA Bus.

The sections in this appendix provide detail on messages and command calculations and strategies that reduce SA Bus traffic.