PLC Technology and Application Tips

Over the past ten years, AutomationDirect, formerly PLCDirect, has provided PLC (Programmable Logic Controller) products in many shapes, sizes, and I/O counts, and with a wide variety of features. Since PLCs were the products on which this company was founded, it is only natural to devote a column on the subject of PLCs in the new Automation Notebook. So, welcome to the first installment of “PLC Speaking”, where we will share AutomationDirect’s insight into PLC technology and pass along helpful application tips from our customers.

Technology and Application Tips

plc_allPLCs have traditionally suffered from the stereotypical complex of “bigger must be better”. However, in the last five to seven years, smaller PLCs in the nano and micro classes have been introduced that have significantly improved capabilities previously found only in larger PLCs. The need to specify a large PLC just for additional features or performance, and not the increased I/O count, is now no longer necessary. Even the smallest I/O count nano PLCs are capable of Ethernet communication, motion control, on-board PID with autotune, remote connectivity and more.

This recent increase in PLC capabilities, found in much smaller packages, has allowed the application of PLCs to go well beyond simple on/off sequential control. Modern PLCs have the ability to perform functions of process control, motion control, data acquisition, RTU (remote telemetry unit) and even some integrated HMI (human machine interface) functions, all in one programmable controller. Previously, each of these functions often required its own purpose-built controller and software, plus a separate PLC for the discrete control and interlocking. For example, the DL06 micro-brick PLC can be a great alternative for a process application that would normally combine a PLC with one or multiple single loop controllers or temperature controllers. By installing either temperature or analog I/O cards into any of the four available DL06 option card slots, and taking advantage of the snap-in LCD display and PID loops built into the CPU, this application can be accomplished with just the PLC and its connected devices. Add an Ethernet module and the PLC can also double as a data acquisition node providing connectivity to any larger plant LAN or WAN information system. Connect a dial-up modem to the secondary serial port and this PLC can be the controller for an RTU as part of a large SCADA system. And, if your application requires motion control, use the integrated high speed I/O to connect a simple stepper system, or install a high-speed counter/pulse output module connected to a servo drive to accomplish a variety of open-loop motion control applications.

Many of these capabilities can be found in new PLCs from most of the PLC vendors around the world. PLC users benefit greatly from increased performance and scalable control capabilities; there are fewer controllers and control programs to maintain, and programs can be reused for multiple applications. This allows quicker installation and easier service of PLC systems, resulting in significant savings in the initial capital expense of hardware and software, and savings in engineering time for system integrators, OEMs, and the end users they serve.

In the next installment of PLC Speaking we will explore the changes in traditional and non-traditional PLC applications that these new lower cost and feature rich PLCs are accomplishing.

I hope you enjoyed this first talk on PLCs and look forward to your survey answers so we may “Speak PLCs” with you again.

By Paul Ruland
AutomationDirect Product Manager
PLC, I/O, Controls Group

Originally Published: Sept. 1, 2004