Intro4u2u

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:

* Greater signal integrity (S/N) by reducing the distance that an analog signals must travel before they are digitised, is important in applications where signal to noise ratio maximisation is demanded.
* Cabling can be simplified and functional sub systems can be modularised. These subsystems can be then plugged into bigger and more complex networks hence simplifying system configuration.
* Remote monitoring of signals or control functions over a corporate or public network is simpler with a DCS architecture as it is naturally packet driven