Upgrading PLCs

Integrator Update: Why wait to replace PLCs without Ethernet communication with little memory for storing troubleshooting data, beyond their supported lifecycle? PLC upgrade advice follows.


Before: On the old control panel, I/O status and alarming were displayed on the front of each control enclosure through square, colored, 24 V dc incandescent lights and connected to the I/O modules. Courtesy: Martin Control Systems Inc.In mass production manufacturing you either stay current with technology or fall behind the times. By keeping equipment/technology current, manufacturing production increases (making more parts in the same amount of time) and downtime decreases (machines run more during a predetermined time), and this adds value to the manufacturer’s bottom line.

As new manufacturing equipment arrived with new technologies, a U.S. manufacturer decided to replace obsolete equipment with new modern programmable logic controllers (PLCs). The older PLCs were still operating but, compared to newer technologies, had limited capabilities, no Ethernet communication, and less memory for storing comments for troubleshooting. And spare parts, no longer manufactured, were difficult to find.

The customer had four control panels for this equipment, each with its own Schneider Electric Modicon 984 PLC and I/O (inputs and outputs). I/O is a common term used to describe the field devices connected to the PLC. (Proximity switches or photo eyes would be inputs; indicator lights or solenoid valves would be outputs). I/O status and alarming (to let the operator know of a fault or problem) were displayed on the front of each control enclosure through square, colored, 24 V dc incandescent lights and connected to the I/O modules. (See first image.) Communications to pass data between PLCs were through hardwired I/O.

Before: Modicon 984 slot-mounted PLCs were actively sold from 1987 to 2006. Courtesy: Martin Control Systems Inc.

The Modicon 984 slot-mounted system (second image) was actively sold from 1987 to 2006. By 2011, spare parts and processors were harder to find and more expensive to buy. The manufacturer decided to standardize the new Omron CJ2 PLC, I/O, and a NS10 HMI (human-machine interface). HMIs allow operators to efficiently see and control various equipment functions, much like a smartphone application that allows control of a race car by touch buttons or certain parts of the screen.

After: Newer PLCs take less space, have more functionality, and are easier to maintain. Courtesy: Martin Control Systems Inc.

On this project, Martin Control Systems:

- Supplied control system engineering services to develop new I/O wiring schematics (showing how to wire from field device to I/O module) using AutoCAD electrical 2011

- Converted the existing PLC program from Modicon to Omron

- Developed an NS10 HMI to replace 24 V dc light clusters in the first image

- Provided installation and commissioning services, which included doing an I/O check, and verifying proper installation to customer standards, equipment start-up, and production support

Third image shows the new PLC equipment. As images 2 and 3 show, the new equipment takes up much less space and requires less wiring.

More functionality, less I/O

Benefits include the following:

  • In the new system the HMIs and PLCs were connected to an Ethernet network, which allowed cross-communication between PLCs and the ability to see alarms within other control enclosures from any of the four HMIs.
  • Obsolete equipment was no longer a problem, and current parts are readily available. Obsolete parts can cost up to five times more than ones that are currently produced. In economic terms it’s supply and demand. As the supply goes down and you’re in demand of the component, you can expect to pay more.
  • The system can be expanded by adding additional I/O modules if called for in the future, and thanks to more memory, program comments can be stored in the PLC for faster troubleshooting.
  • I/O was reduced by moving all the indication lights (image 1) to the new HMI. There’s no more wondering if there is an alarm or if the light is burned out, so no more purchasing and stocking of light bulbs.
  • With having the system on an Ethernet network, it can be connected to a data collection system to receive and store real-time machine information and alarms. 

- Jim Sellitto is project manager/principal, Martin Control Systems Inc. Edited by Mark T. Hoske, content manager, CFE Media, Control Engineering and Plant Engineering.


Technology links

- Schneider Electric automation and control news: Upgrade Modicon PLCs and keep LL984 applications

Omron CJ2 PLC

- Omron NS10 HMI

AutoCAD Electrical

- Control Engineering January cover story: Control system software programming

- controleng.com/PLCs

(This was originally posted May 18, 2012. Date was changed for inclusion in a newsletter.)

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