- 4 -
3. F
UNCTIONAL
D
ESCRIPTION
3.1 Overview
The Mux2700 HART Signal Multiplexer (HSM) provides 32 signal channels for connection to field located, “smart”
transmitters or control devices supporting digital communication according to the HART standard. The Mux2700
acts as a gateway between a Maintenance Workstation (MW) – typically a PC with suitable SW – and the field
instrumentation. The MW connects, in a multi-point configuration, with up to 31 Mux2700 using a fast RS-485 com-
munication channel.
The HART protocol is a widely accepted technique by which standard 4/20 mA field devices can support digital
communication for configuration and maintenance purposes. A modulated, audio-frequency signal (Bell202 FSK) is
in fact superimposed to the analogue current loop providing a 1200 baud, half-duplex communication capability.
The HART protocol, being a widely accepted standard specified up to the application layer, permits an effective
integration, at the Maintenance Workstation level, of field devices from different manufacturers.
The Mux2700 HSM not only uses the HART protocol to communicate with the field devices but also to interface
with the Maintenance Workstation via an RS-485 link. In this way, an highly standardised solution is obtained.
Under the supervision of the Maintenance Workstation, the Mux2700 interrogates each field device, retrieving infor-
mation which are then stored in an internal data-base. This internal data-base can then be accessed in real-time by
the MW which however, when required, can also directly communicate with any specific field device.
IM-ENG-116/GB
