Another factor helping boost the PAC’s task load is the large
volume of memory that now fits on a single card. The Allen-
Bradley ControlLogix L65 from Rockwell was upgraded to 32
Mbytes. This helps in information-intensive applications like
batch processing, where added capacity provides more capability
for recipe management.
Easily accessible memory can bring a number of benefits for
plant managers. Some aren’t dramatic technical capabilities, but
they’re important nonetheless. PACs can store documentation on
each piece of equipment so operators can quickly access instructions
for tasks they aren’t familiar with.
Similarly, maintenance technicians can quickly access information
they need. Storing these files directly on the system assures
managers that personnel are using up-to-date documentation,
reducing problems when misplacing books or disks.
Though PACs handle many
complex tasks, important facets
of control still run on other
controllers. Most PACs currently
don’t have human-machine
interface (HMI) capabilities,
which typically run on dedicated
processors. Many contain proprietary
interfaces, though the
industry seems to be migrating
to commercial operating systems
such as Windows CE.
That’s likely to change, bringing
tighter integration and
eliminating the physical space
required by separate controllers
while reducing the memory
space required for a dedicated
operating system. “As we go to
dual-core and multicore processors,
it’s possible that a processor
can handle the HMI and conventional PAC tasks,” says Derstine.
NETWORKED WORLD
Another key benefit of modern controllers is their connectivity.
The drive to eliminate duplication of effort has made Ethernet the
standard throughout most corporations. Extending Ethernet to
the factory floor makes it simpler to link equipment in the plant to
front office computing. That means inventory data and orders can
use the same data files, wiping away the problems that may occur
when data must be re-entered for different architectures.
Industrial managers, as a result, can reap many benefits. They
no longer have to deal with a multitude of networks, and the
compatibility with TCP/IP makes it possible to tap into any
piece of equipment regardless of where it’s located throughout the
global enterprise. “With PACs, you can bring up a browser and see
what’s going on from your home or a remote office. You can’t do
that with a PLC,” says NI’s Veeramani.
This freedom creates further challenges for the engineers who
design industrial controllers. Ethernet connectivity is a must, but
several technologies still use a number of field buses, including
DeviceNet, Profibus, AS-Interface, and Interbus. Moreover, realtime
Ethernet alternatives require some minor tweaking in addition
to conventional Ethernet installation efforts.
Product developers are doing everything they can to let controllers
communicate with many of these networks. “One requirement
for a PAC is openness, being able to talk to any bus, any industrial
network,” says Veeramani. And, companies continue to extend
their offerings in this area.
Opto 22’s SNAP I/O Systems now communicate via Allen
Bradley/Rockwell Automation’s Ethernet/IP (Fig. 4). Functions
like high-speed counting and latching, quadrature inputs, pulsing,
thermocouple linearization, and proportional-integral-derivative
(PID) loop control can be distributed to the I/O level so the central
controller needn’t address these time-consuming tasks. The
Opto 22 PAC can serve as a slave or adapter, sharing data with
Ethernet/IP-enabled devices.
Nearly all PACs require this type of connectivity. The Bosch
Rexroth IndraControl L10 is a low-end board that’s designed to
be compact, but it still includes Ethernet connectivity and talks to many field buses (Fig. 5). “With our PLCs, you can talk to
any network. It’s relatively transparent to the user which network
they’re using,” explains Ted Thayer, PLC product manager at
Bosch Rexroth.
Controllers are also taking advantage of increases in Ethernet
bandwidth. CC-Link leverages the Gigabit Ethernet standard
that pushes bandwidth up by a factor of 10. Mitsubishi is a primary
proponent, and others are expected to employ the latest commercial
version of Ethernet in industrial environments. Until that
happens, plant managers are using real-time versions of Ethernet
to gain determinism. Engineers exploit the enhanced capabilities
to add more nodes to their networks and manage more tasks.
“Users are improving their systems by designing larger network
segments, simplifying maintenance and programming on the total
architecture. They can also implement multifunctional networks
by running different applications like I/O control, video, and
HTTP on the same wire,” says Scott Tenorio, Logix product manager
at Rockwell