Emerson Controlinc Network Master Model M250 Version 5.2

Introduction

Emerson Controlinc Network Masters are the master of Emerson Controlinc valve

actuator networks with Modbus RTU protocol. The system provides network management,

data concentration and protocol conversion, off-loading the host system of these tasks.

This enhances overall system performance and minimizes software development and

system configuration tasks by the system integrator. The Network Master serves as the

master of a master/slave network. It manages the network by keeping an orderly

cycle of data transfers to and from the slave devices (valve actuators).

It handles error detection, alarming, and network recovery.

The Network Master serves as a data concentrator for the host by providing a common

database for all slave devices. The host is required to communicatewith only one slave device

(network master) for all data transfers to and from the field.

Data can be transferred between the network master and host in large blocks at a much

higher communications rate than would be possible if the host communicated with each

slave device (valve actuator) on the field network. The Network Master acquires data from

the valve actuators by polling or scanning each device in a sequence of slave address from

a table called a scan list. Polling is a process of the Network Master sending to each slave

address, a command to return its status information, including alarms, discrete and analog

inputs and outputs. When control commands (valve open, stop, close, position set point, etc.)

are generated by a host system up-line of the Network Master, it then sends the appropriate

commands over the network to the addressed slave device. A more detailed functional

description of operation is provided in the Theory of Operation section of this manual.