Voices: Bacidore

Safety Relays or Better Diagnostics?

Where Do Machine Builders Draw the Line Between Diagnostic Needs and Safety?

Mike BacidoreBy Mike Bacidore, Managing Editor

A downside of safety relays can be the lack of diagnostics they provide. When the machine stops, you still have to go out and do some troubleshooting, find and repair the problem, and then restart the machine. But where do machine builders draw the line between diagnostic needs and safety?

"We use a lot of safety relays," says Jim Braun, vice president, product development and standardization for MAG Americas (www.mag-ias.com), Hebron, Kentucky. "We also have safety integrated on our machines, which you're doing through safe PLCs and specific logic. It adapts well on some machines and not on others. You see a lot of safety integrated on European machines."

Being a global company, MAG builds a lot of machines in and for Europe. "In the U.S., we still do a lot of safety relays," says Braun. "Our experience is that the relays are pretty reliable. If there's a problem, they're a little more difficult to troubleshoot. The trend in the industry is going more to safe PLCs and safe drives. You have this whole regimen of software you go through. Over time that will tend to eliminate the safety relays. Safe PLCs and safe drives can be more cost-effective."

Jack Chopper, chief electrical engineer, Filamatic (www.filamatic.com), Baltimore, believes the lack of diagnostic information will be a short-lived problem. "Diagnostic capability is always a time-saver, but the safety integrity and reliability must override the other information-related features," he says. "The safety-rated PLC is relatively young and still very pricey, but as those types of products mature, they will settle down in price."

Diagnosing a problem determines the root cause of a potential or pending failure, explains Hilton Hammond, product manager—ScopeMeter, Fluke (www.fluke.com). "Safety components, by design, are built into a system to ensure, in the event of a failure, something catastrophic does not occur that could present a hazardous condition to the operator or the surrounding environment," he explains. "Sensing and measuring critical variables, like voltage or current, and applying them to some form of a diagnostic algorithm, can provide the user feedback about the operating state of the machine or process."

Without a relay, interlock or other protective device built into the active circuit, a shutdown could be delayed, which might result in an unacceptably hazardous condition, says Hammond.

"My first safety relay system had more than 30 relays in a cabinet," recalls Wade Peterson, electrical engineer, CMD (www.cmd-corp.com), in Appleton, Wisconsin. "It took two days to fully commission that system. But we became a lot more proficient at it and got to the point where the same job would take only four hours. Better diagnostics would have helped in the first situation but would have been of less use toward the end after the initial learning curve was overcome. Diagnostics should be a concern when there are a variety of devices or if maintenance resources are scare. Product longevity and reliability are more important in safety circuits when component standardization and good training are in place."

Traditional safety relays can be problematic, says Helge Hornis, PhD, manager, Intelligent Systems Group, Pepperl+Fuchs (www.pepperl-fuchs.com). "AS-Interface offers a safety solution—Safety at Work—that enables very detailed diagnostics down to the contact level," he offers. "Using this solution for safety applications, it is easy to find sticky contacts. All it takes is a few rungs of PLC logic."

There are more downsides to safety relays than just the lack of diagnostics from the relay, warns Kurt Wadowick, I/O systems specialist at Beckhoff Automation (www.beckhoff.com). "With outdated relay technology, safety system designers also need accurate electrical drawings, a trained electrician who can read those drawings and at least a digital multimeter to test the circuits that are in doubt," he explains. "In contrast, distributed and automated safety components with proper configuration can point out faults automatically. This enables the electrician to immediately understand which component has failed and focus attention on repairing the actual failure point instead of spending excessive time trying to find that failure."

More From This Voice

Title

Safety Relays or Better Diagnostics?

Where Do Machine Builders Draw the Line Between Diagnostic Needs and Safety?

08/30/2010

Two Controls Engineers Discuss Servo Motors

Servo Motors Are Good for a Change: Machine Builders Discuss the Pluses and Minuses of Using Servos

07/15/2010

Environment Could Affect Choice of Terminal Blocks or Their Enclosures

Protect Your Terminal Blocks: Potential Corrosion and Vibration Impact Which Choice Is Best

07/01/2010

Heavy Transporter Wins Control Design Innovator Awards Competition

Size and Shape Matter in Material Moving: Doerfer Designs and Builds Innovative Transporter to Move Enormous Loads in Plant Environments

06/22/2010

Diagnostic Tools Are Only As Good as the Display That Operators See

HMI Plays Role in Diagnostics: Engineers Can't Troubleshoot Problems Without an Operator Interface That Tells Them What's Wrong

04/07/2010

Is Redundancy Necessary or Superfluous?

Unnecessary Redundancy?: The Value of the Product or the Critical Nature of the Process Can Warrant It

03/10/2010

Fiberoptic, Wireless Connections Require Special Considerations

Fiberoptic, Wireless Raise Hackles: Connecting Machines to Networks or In-Line Systems Can Be Tricky, Depending on the Media

03/09/2010

Elephants Are the Answer- Part II

Where the Chinese Excel at Producing Things, It's No Secret That the Quality Often Is Horrendous. Their Acceptable Standards Aren't the Same As Those in Western Countries

02/16/2010

Industrial Computers Need a Variety of Features, Depending on the Use

Features Depend on the Application: While Harsh-Environment Protection Is Critical, Other Elements Can Be Equally Important

01/20/2010

Entry Into the Chinese Machine-Building Market Might Be Explained by Elephant Jokes

The Chinese Machine-Building Market Is Like the Giant Elephant in the Middle of the Room; Entering That Market Is No Joke

01/05/2010

Controls Networks and IT Networks Need to Work Together for Effective Supply-Chain Management

Siblings Can Learn to Play Nicely: Companies Are Turning Clashes Into Cooperation Between IT and Manufacturing

12/08/2009

Machine Builders With Fewer Employees Have Less Time to Investigate New Technologies

Farm Fresh Machine Automation: An Economic Downturn Normally Offers an Opportunity to Retool and Investigate New Technologies, but This One Is Anything But Normal

11/02/2009

Software Replaces Machine Hardware, but Mechanical Solutions Still Have Their Places

Where Has All the Hardware Gone?: As More and More Mechanical Systems Are Replaced, Is Software the Final Frontier?

10/08/2009

Vote for the Innovative Machine You'd Like to Hear More About

Place-and-Show Corral Full of Thoroughbreds: The Runners-Up in Our Annual Innovator Awards Have Great Stores to Tell

08/31/2009

Design Controls for Your Career

Whatever Measures You Can Take to Retain Your Workforce, Rather Than Have a Reduction in Force, Are the Right Things to Do

08/06/2009

With Great Power ...

Organizations That Opt for High-Power PoE Products Are Purchasing Products That Are Not Standards-Based

08/04/2009

Control Logic's ValuRip Plus and TGW-Ermanco's Turbo Sorter Earn 2009 Innovator Awards

Breakthrough 2009: This Year's Recipients Employ New Technology to Make a Difference for Their Customers

07/06/2009

Hydraulics Get Better With Age

Hydraulic Systems Improved Over the Years Offering Tighter Tolerances and Better Fault-Sensitivity

06/15/2009

PC-Based Controls Choice Still Evolving

Decade-Old Debate Over PC Vs. Dedicated Controller Still Rages

04/30/2009

Virtual Intelligence Tackles Motion Control

Control Intelligence Agency Virtual Brigade Member Comments on Results of our Market Intelligence Report

03/30/2009