IEEE
1394 AND INDUSRIAL AUTOMATION
A Perfect Blend
The
industrial automation community can benefit in many ways by taking a
close look at how 1394 has benefited the world of consumer electronic
devices, explains Gaurav Sareen.
Introduction
IEEE
1394 emerged as a serial bus standard in 1995, after being initially
defined as “Firewire” by Apple. Rapidly it became the bus
of choice for the Digital Consumer Electronic manufacturers owing to
its extremely high data transfer rates (up to 800Mbps) and support for
real time data streams. The dream of being able to Internet work all
Consumer Devices in a home became a possibility with 1394 as Peer-Peer
communication became a reality. The guaranteed delivery of data coupled
with other above-mentioned advantages made 1394 a boon for Multimedia
applications. IEEE 1394 is now suitably positioned to move into the
orbit of Industrial Automation Systems and to radically change the approach
to automation control design by challenging conventional bus technologies.
Traditional
Automation Control Architecture
Current
solutions in industrial automation and instrumentation can be characterised
as centralised and backplane oriented. Backplane based controllers were
considered to be natural choices for the designers of yesterday, as
it was assumed that they could provide high communication speeds needed
for industrial processes like synchronising motion, synchronising images
and data acquisition. The rack mounted back plane, which is the standard
implementation for 
most
Industrial and Laboratory Automation controllers, uses bus solutions
like VME, VXI, and PXI apart from proprietary buses like Modbus. In
recent times, PCI buses have gained popularity in this market segment
owing to the penetration of Windows based PCs. In the conventional architecture,
all sensors, motors, digital inputs and outputs and analog signals are
cabled from the point of use to converge at the centralised controllers
with individual backplane cards designed to handle each specialised
function. All signals are brought to the physical location of the system
controller using multi-wire cable bundles. Figure 1 is a schematic of
a Typical Automation Machine System with 6 axes of motion control, machine
vision and process control.
These
types of Machine Systems typically use several specialised backplanes
to implement different control functions. Bus to bus communication between
various subsystems is often through traditional RS-232/422/485 serial
communication channels or through bus converters. This centralised approach
limits reliability and configurability as hundreds of conductors are
required to route signals to the central control chassis.
Overall this traditional approach is cumbersome, physically larger and
is expensive
with prices in the is cumbersome, physically larger and is expensive
with prices in the range of $10,000 to $30,000 depending upon performance
specifics. Another big problem is the software used for controllers.
Due to the lack of standard interfaces, different vendors follow different
software approaches to develop various subsystems and to integrate them
proves to be expensive and time consuming.
Distributed
Control Systems
To
avoid the use of a centralised back plane based system, it is important
to localise control of devices performing similar functions. This Distributed
Control System (DCS) architecture uses some form of serial or parallel
cable to link the already digitised information from point of use. In
DCS, analog signals are quickly digitised, and functions that do not
need to be centrally supervised are localised.
The
advantages of using DCS are as follows:
