 |  |  |  |  |
Using Personal Computer technology as a logic controller
PCs as replacement
for PLCs was
thought to bring
cost savings and
other advantages.
Result has actually
been the
appearance of PC
functionality in
PLCs.
replacement of specialized PLC systems with PC-based (personal computer) for
automation control. This market development is driven primarily by the continuing
reduction in PC hardware prices and their continuing increase in computing power.
Another motivating factor of PC usage is the perceived ease of integration and
networking of PCs and their user-friendly interface.
The result on the automation industry has actually been the flip side of the original
motivation, instead of using PCs (although they are being used and one
automation supplier specializes in this supply) the primary affect has been the
appearance of PC-type functionality in the PLCs. PLCs are now capable of
integration into business networks, web hosting, ethernet communication, multiple
language programming, etc. This has even motivated some suppliers to try to
change the name PLC to something more indicitave of the hybrid-type products
currently available.
The use of PLCs largely remains the status quo because although the
attractiveness of PC-based control is increasingly feasible, it is largely not yet as
reliable or cost effective as PLC control for most automation tasks (one of the
primary challenge iss the processing nature of PCs compared to the sequential
looping of PLC execution and the related CPU loads). Acordingly most automation
tasks require an industrial PC workstation and highly specialized programming
which tends to offset the original intention of cost saving via standard COTS
hardware and software. That being said, the line between PLC and PC is
increasingly fuzzy and it is clear that the future of automation control will continue
to demand PC-type functionality of control equipment regardless of
Lessons for Railroaders:
1. Much of the talk about PC-based control has resulted more in the appearance
of PC-type functionality in control equipment that actual PC equipment in control
environments. The distinction between control equipment and personal
computing continues to disappear. Suppliers proposing PC-based control systems
should be thoroughly scrutinized regarding system reliability and resultant cost
advantages.
2. True PC control may be coming but it remains something that is probably
several years away.
