consideration. A wide variety of hardware options is
an example, such as many types of discrete and analog
I/O, and multiple communication ports. Even though the
current application may not require all of these features and
options, the next application may. The ability to stay with
a common platform across applications may save time and
money, so it’s often best to look for a family of controllers,
rather than a single model.
Low-cost, brick/stackable controllers often provide only
predefined data types and related data tables. This works
well for simple control and monitoring applications, but a
tag-based memory with no pre-defined memory addresses
is often preferred. Controllers with tag-based memory
allow a user to choose how to use the controllers’ processor
memory for Boolean, integer, string or floating-point data
types—a helpful option for more complex control.
Communication needs should be defined, and more is
better in the world of the Industrial Internet of Things.
The ability to integrate other control devices with a
programmable controller may be a huge factor when
choosing a platform. Whether using communication such
as MODBUS or EtherNet/IP, or choosing a controller that
can auto detect remote I/O and variable frequency drives,
simplifying device setup should be considered during the
Communication from a programmable controller to
other devices or enterprise systems should be carefully
considered, especially if it may be necessary to collect data
from a machine or process with the PLC. The data starts
out local and can be collected there and used, but often
also needs to be sent elsewhere. The data logging feature
in some controllers can be accessed via a local USB port
or a removeable media storage device. Another option is
browser-based access via an Ethernet network and a built-in
Whether the user wishes to monitor production or use
data metrics to fine tune an application, the capabilities
of a system to save and allow the user to collect this
information is often an important factor when choosing
a platform. The industry has seen a rapid change from
local to remote accessibility with the common availability
of Internet connections in industrial settings, along with
wireless connectivity in more remote locations. Being able
to collect data locally and retrieve it remotely via a web
browser or a remote data collection server is a must for
many automated systems.
The ability to remotely connect to a PLC should also be
considered as its often needed for making program changes
or fine tuning a process during commissioning. When
monitoring a system that is not geographically convenient,
or troubleshooting equipment several hundred miles away,
being able to connect to a controller remotely may be a
When comparing controller families and platforms, a
major factor should be the ease of learning options and
features. The availability of a common software platform
capable of use on multiple controllers is important if
multiple applications are planned that vary in size or
complexity. A single platform provides the ability to
convert projects across controller platforms. This enables
existing code from one controller to be used in a different
controller within the family without having to manually
reenter the code.
Specialty instructions in the programming software
can also be a huge time saver, as this allows simple
configuration instead of more complicated programming.
Utilities built into the software can simplify implementation
of specific features such as tuning PID loops or testing high
speed I/O, saving a considerable amount of time during
design and commissioning. Being able to scale an analog
input or perform an average on a variable without needing
to program multiple math instructions can also save quite a
bit of time.
Software with automatic discovery of hardware, along
with automatic tag creation for the hardware points, makes
setting up a system much quicker. A platform using a
tag database allows use of name tags with information,
automatically documenting the code, very important for any
user needing to troubleshoot the system in the future.
With a common software platform, there are options
to scale an application up or down. An abundance of
communication options enables remote I/O, control of
variable frequency drives and other capabilities. Additional
Ethernet and serial protocol options, along with custom
protocol setups, add to communication flexibility.
Time and effort spent up front researching controller
families and platforms, both the hardware and the
programming software, will pay off in the long run with
improved ease of use and greater flexibility.
Winn Paulk is the Automation Controls Group Product
Manager at AutomationDirect.