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Functionality and Applications
The use of logic controllers in factory automation to replace relay logic began in
Europe and the U.S. in the late 1960s, spurred primarily by the automotive
industry. Although relay control had proved a reliable control method its demise
was ensured by its most attractive feature - simplicity. Factory and process
automation companies are forced to frequently retool and/or re-organize their
automation tasks (as opposed to railroads) due to new production models,
products, use of different "widgets" in the process, etc. This is an incredibly
complicated task when dealing with huge racks of relays and the amount of wiring
inherently required. These relay applications also often required application-specific
hardware which must be swapped out when migrating to a new process
application. They also tended to require complicated and supplier-specific
communication methodologies (sound familiar...think codelines). Accordingly logic
controllers were introduced under the promise of hardware re-use, and less
complicated applications, all while increasing availability.
The use of these logic controllers (now frequently called PLCs) was immediately
successful and their widespread use had essentially rendered relay logic in factory
automation applications obsolete by the end of the 1970s. This development also
paved the way for another interesting area - robotics, in which the logic itself is
implemented into the process machine.
Railroads, by contrast, where much later in applying digital controllers in place of
relays. This lag is often attributed to the safety requirements of railroads (i.e. the
wait for a vital platform) but also has something to do with a continued affinity for
relay logic in the absence of the pressures mentioned above on the process
industry. Railroads rarely change any fundamental processes, and have very little
variance in the type of equipment they are controlling. The result is that the first
vital electronic interlocking was not installed an U.S. Class I railroad until the
mid-80s and to this day certain railroads continue to install primarily relay control
systems.
The twenty year head start which the automation industry has on railroad
automation, combined with the myriad of different controlled devices and
environments seen in the automation world results in a large functional gap
between factory and railroad logic controllers. While lacking the specialized
interfaces required by the U.S. railroad environment (i.e. coded track circuits, signal
control, etc) automation products offer a breadth of capabilities and functions far
beyond that of todays electronic interlocking products. In contrast railroad
wayside controllers have evolved relatively little over the last ten years and the
focus on these products has been on simplicity. There is also very little pressure to
modernize wayside controller system platforms on the part of suppliers due to the
relatively small number of competitors, the somewhat isolated nature of the
signaling industry, and the lack of pressure from railroads for increased
functionality. It is therefore of value that railroads keep abreast of the functional
developments in the automation industry, such that they can adequately judge
the capabilities and direction of evolving technologies and subsequently
communicate functional requirements which will assist the railroad in achieving its
goals, and railroad suppliers to develop adequate productss.
Todays' industry automation platforms are not your father's PLC. The most
obvious development in recent years is the hardware architecture of modern
platforms. Modern PLCs tend to me small, scalable, and modular. The hardware
can be tailored exactly to the application requirements (in terms of CPU power,
I/O, and communications needs), and modularly expanded as necessary - for
example the addition of four more I/O points. One of the ways this is achieved is
via the use of a thru-plane instead of a cardfile mother-board type architecture.
The system bus is resident directly in the system components which are physically
connected on the side of each new module. Given the small physical size of the
modules available (less than half the size of the cardfile dimensions railroaders are
familiar with) this modular architecture leads to a optimization of physical space (no
need for a rack and no need to access the rear of a cardfile means that the
equipment can be mounted directly on a wall).
This feature, in combination with a few of the ones mentioned below, is leading to
system architectures which can only be called "extremely distributed". From I/O
modules and interface modules with integrated processors, to internal systems
communications which can be applied over several mediums (for example copper,
fiber, radio, WLAN, etc) and are fast enough to truly distribute all components,
modern automation platform provide for a flexibility in system design that is almost
unlimited. These schemes are also often integrated into redundant architectures
which allow for any imaginable combination of redundant processors, redundant
I/O and other components in cold-, warm-, or hot-standby.
In terms of hardware, modern automation platforms also tend to demonstrate
advantages over railroad wayside platforms in areas such as reliability and power
consumption. Not surprising given the sheer economies of scale of the
automation world in comparison with the production of most wayside controllers.
Regarding the software user interface and programming functionalities of modern
automation platforms it can only be said that - in comparison to railroad controllers
- the functionalities and features are not only mind-boggling but actually simple to
use. Despite the inherently higher functionality, the development environment of
these platforms is normally much more elegant and inuitive than that of wayside
controllers and can be learned by anyone with normal PC experience relatively
quickly. Most platforms offer several different programming languages, structured
and modular programming which is easily re-useable. Some products come with an
abundance of pre-programmed functions that can be used if desired, although for
railroaders these are generally uninteresting as they are usually geared more to the
automation industry-type need for controlling analog I/Os, PID loops, etc.
(generally the kind of talk railroad signal engineers like to avoid!).
However, the most interesting characteristic of modern automation platforms is
the ability to integrate functions which used to belong to a separate
communications system. Without a doubt the networking and communications
capabilities of modern PLC platforms is one of the most promising areas of
development for the automation world and for railroads. PLCs provide for the
capability of communicating over several networks and mediums. For example,
with a modem attached to a PLC, it is possible to remotely troubleshoot, exchange
data, and even program and test from a location on the other side of the world.
(see also The disappearing fieldbus) System components such as control panels,
etc can be hundreds of miles from the controller itself. Many modern automation
platforms have even begun to appear with the integrated ability to host websites
directly from the PLC, some even with JAVA functionality (anybody see where this
is headed...?). Attach this to your companies' business network and you can pull
up an Intranet page hosted by a controller and showing you whatever information
you have requested. Depending on the communications network, some suppliers
have even implemented control over these intra- and internet sites. Even without
a webserver, the PLCs integration in a business network is ever-increasing,
including the ability to send emails to pre-programmed recipient in the case of a
failure or other event. The implications for future applications are not hard to
imagine, especially for railroads.
Lessons for Railroaders:
1. Stay informed of the automation industry, simply due to its size and nature it is
way ahead in terms of technology and can provide you with a look into the future
of wayside systems and help you to communicate requirements to suppliers.
2. Automation platforms hardware systems are small, scalable and distributable
and not confined by cardfiles or cages. User interfaces and architecture capabilities
are far beyond that of existing U.S. wayside platforms.
3. Especially of interest to railroaders is the communications capabilities of modern
automation platforms. Why drive 100 miles to a site to find out that you don't
have the right board to replace? The advantages that the integration of your
wayside equipment in your business network would provide include remote
diagnostics, maintenance, and testing.
Digital logic
controllers began to
replace relay logic in
factory automation in
the late 60s.
The first Class I
electronic
interlocking was put
into service in the
mid-80s.
PLCs are more
powerful and
versatile, Wayside
controllers are more
specialized and simple
Modular, scalable,
and distributed
hardware
Distributed logic
Programming user
interface
Communications and
networking
& HMI
fieldbus
relay, microlok, vhlc, geo, networking, data reporting, vpi, vhlc, geo, microlock, microlok
