SA Bus device limits - Metasys - LIT-12011034 - General System Information - Metasys System - Release 11.0

MS/TP Communications Bus Technical Bulletin
Product
Building Automation Systems > Building Automation Systems > Metasys System
Document type
Technical Bulletin
Document number
LIT-12011034
Version
Release 11.0
Revision date
2022-02-07
The guideline for the maximum total number of devices supported on an SA Bus is 10. The following three factors support this guideline:
  1. The SA Bus has additional device-specific limitations based on the number of possible addresses supported by a specific SA Bus device.
    Note: The NS8000 series supports up to eight addresses.
  2. The power consumed by specific SA Bus-powered devices versus the maximum power supplied by the host controller.
  3. The change of value (COV) transmit rate of a specific SA Bus device.
Important: The total power consumption for the SA Bus is limited to 210 mA on the SA Bus modular jack and 240 mA on the SA Bus terminal block. Exceeding the total power consumption limit can cause poor bus communication and cause devices to go offline.

Table 1 provides information on the power consumption of devices commonly connected to the SA bus.

Table 1. Power consumption by common SA Bus devices

SA Bus device

Power consumption on the SA Bus

Discharge Air Sensors (NS-DTN70x3-0)

12 mA

Balancing Sensors (NS-ATV7003-0)

25 mA

Network Sensors - Base current draw (graphical model) Screen off

 18 mA maximum (non-transmitting)

Network Sensors - Base current draw (graphical model) Screen on

 45 mA maximum

Network Sensors - Base current draw (other models)

3 mA maximum (non-transmitting)
CO2 Network Sensors - LCD graphical 13 mA maximum additional current (during measurement)

CO2 Network Sensors - (other models)

 15 mA maximum additional current (during measurement)
Network Sensors - Fixed segment display models - backlight on

10 mA additional current

Network Sensors - Warmer/cooler models - LEDs on

8 mA additional current

Mobile Access Portal (MAP) Gateway

180 mA

DIS1710 Local Controller Display

90 mA - may be a temporary load

Variable Speed Drives

NA (self-powered)

IOM/XPM Series Controllers

NA (self-powered)

Romutec® Modules

NA (self-powered)