PCs versus PLCs for process control

Soapbox: Don’t settle for faults inherent in PLCs and PCs. Take the best of each for a more effective hybrid system for process control, according to a software and hardware provider to the process industries.

12/19/2011


PLCs have been an old-time favorite for automation and control. The top-down programs and input-output type of ladder logic offered reliable control of process. However, with the ever-growing need for production information and quality control, the inadequacies of the PLCs were exposed.

Turbomation engineers software and hardware integrated systems; hybrid PC and PLC control systems are more popular than ever, the company says. Courtesy: Turbomation

Enter the PC as a tool for automation and control. The PC, with its user friendly operating systems, looked more like a candidate to displace the PLCs. However, the reliability of the operating systems left a lot to be desired. If working on a word processing document and the PC freezes, it is simple to hit the reset button. This, however, is not an acceptable solution when a PC-controlled machine is reaching dangerous operating conditions. Hence the PC is not an answer for process control.

The PLC is inadequate when complex mathematics is required. PLCs do not handle image analysis well either. Even process control like temperature and pressure are not well handled by PLCs where high levels of accuracy are needed. This kind of temperature and pressure control is better left to intelligent field devices like dedicated temperature or pressure controllers. Recently PLCs have been benefitting from special process control modules that may be added to PLCs. One thing that PLCs do very well is discrete control like opening and closing valves. PLCs have been fairly efficient in positioning for robotics.

In short, the question is how to integrate the reliability of the PLC’s discrete control, the precise control of intelligent field devices, and the processing power of the PC. The obvious answer is a hybrid system with the PC as the supervisory device with delegated controls to the PLC and other field devices.

All calibration, data analysis, and data history are handled by the PC. The human machine interface is provided by the PC. Actual process control is carried out by the PLC and the field devices best suited for the application. With the advent of interdevice communication capabilities, hybrid control systems are more popular than ever.

This way the best capabilities of all the devices are safely leveraged for the best results. This model also lends itself to cloud-based remote control or data acquisition.

- Jacob George is application engineering manager at Turbomation, a company engaged in engineering and automation consultation for process control. Edited by Mark T. Hoske, CFE Media, Control Engineering, www.controleng.com.

www.turbomation.com 

http://controleng.com/process 



No comments
The Top Plant program honors outstanding manufacturing facilities in North America. View the 2013 Top Plant.
The Product of the Year program recognizes products newly released in the manufacturing industries.
The Leaders Under 40 program features outstanding young people who are making a difference in manufacturing. View the 2013 Leaders here.
The new control room: It's got all the bells and whistles - and alarms, too; Remote maintenance; Specifying VFDs
2014 forecast issue: To serve and to manufacture - Veterans will bring skill and discipline to the plant floor if we can find a way to get them there.
2013 Top Plant: Lincoln Electric Company, Cleveland, Ohio
Case Study Database

Case Study Database

Get more exposure for your case study by uploading it to the Plant Engineering case study database, where end-users can identify relevant solutions and explore what the experts are doing to effectively implement a variety of technology and productivity related projects.

These case studies provide examples of how knowledgeable solution providers have used technology, processes and people to create effective and successful implementations in real-world situations. Case studies can be completed by filling out a simple online form where you can outline the project title, abstract, and full story in 1500 words or less; upload photos, videos and a logo.

Click here to visit the Case Study Database and upload your case study.

Bring focus to PLC programming: 5 things to avoid in putting your system together; Managing the DCS upgrade; PLM upgrade: a step-by-step approach
Balancing the bagging triangle; PID tuning improves process efficiency; Standardizing control room HMIs
Commissioning electrical systems in mission critical facilities; Anticipating the Smart Grid; Mitigating arc flash hazards in medium-voltage switchgear; Comparing generator sizing software

Annual Salary Survey

Participate in the 2013 Salary Survey

In a year when manufacturing continued to lead the economic rebound, it makes sense that plant manager bonuses rebounded. Plant Engineering’s annual Salary Survey shows both wages and bonuses rose in 2012 after a retreat the year before.

Average salary across all job titles for plant floor management rose 3.5% to $95,446, and bonus compensation jumped to $15,162, a 4.2% increase from the 2010 level and double the 2011 total, which showed a sharp drop in bonus.

2012 Salary Survey Analysis

2012 Salary Survey Results

Maintenance and reliability tips and best practices from the maintenance and reliability coaches at Allied Reliability Group.
The One Voice for Manufacturing blog reports on federal public policy issues impacting the manufacturing sector. One Voice is a joint effort by the National Tooling and Machining...
The Society for Maintenance and Reliability Professionals an organization devoted...
Join this ongoing discussion of machine guarding topics, including solutions assessments, regulatory compliance, gap analysis...
IMS Research, recently acquired by IHS Inc., is a leading independent supplier of market research and consultancy to the global electronics industry.
Maintenance is not optional in manufacturing. It’s a profit center, driving productivity and uptime while reducing overall repair costs.
The Lachance on CMMS blog is about current maintenance topics. Blogger Paul Lachance is president and chief technology officer for Smartware Group.