August 2008

®PlantEngineering.com

P lant engineers are taking advantage of new machine guarding technologies endorsed by international safety standards. From the most sophisticated manufacturing operation to the

simplest relay-based system, machine manufacturers and end users now have economical and effective choices to enhance machine safety.

The latest options include integrated, networked safety systems using reliable safety PLC technology. Designed and built according to IEC guidelines and tested by a nationally recognized testing laboratory, safety PLCs, buses, I/O and other components are replacing traditional hardwiring on machines.

The most important benefit of integrated, automated machine safety is enhanced operator protection. The National Institute for Occupational Safety and Health (NIOSH) reports that fatality rates from machine-related accidents were second only to motor-vehicle-related acci-dents, and recorded higher fatality rates than homicides, falls and electrocutions.

Safety standards drive changesRecent developments to machine safety include chang-

es in standards from the National Fire Protection Agency. In the fall of 2002, NFPA 79 was re-published providing application guidance for failsafe, or safety-rated PLCs and safety-rated busses to be used in functional safety applications.

It also established requirements for a risk analysis to be performed on all machinery and described E-stops as a part of the safety design. All safety-rated devices could thus be installed on a safety-rated bus.

These changes allow manufacturers to develop power-

ful new solutions that replace hardwired relays with PLC safety circuits that have built-in safety functionality. This built-in safety greatly reduces cost, requires less time to implement and increases machine uptime.

The risk analysisIn 2004, ANSI B11 TR4-2004 was approved. It pro-

vides application guidance for safety-rated hardware and software-based devices in functional safety applications.

Machine safety pays off

By J.B. TitusSiemens Energy & Automation Inc.

If a manufacturer’s downtime costs $10,000 an hour, it does not take long to justify a low-cost, integrated system that saves time and increases uptime

Dedicated safety relays

Functionality vs. cost of ownership

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Cost of ownership can be very different than initial product cost. The chart indicates that total cost of ownership for integrated safety PLC systems is inversely proportional to functionality.

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These and other standards reference IEC 61508, 62061, 60204-1 and EN 954-1 (which will be phased out next year) – many requiring a formalized risk analysis to estab-lish risk reduction methodologies. ISO 13849-1 2006 will replace EN 954-1.

The risk analysis formalizes what some companies had been doing all along – even though the assess-ment wasn’t considered an absolute standard. It was once assumed that people would follow due diligence and engineering principles to pro-vide a safe workplace, as required by OSHA.

Now, a formal risk assessment process, as described in the ANSI Z10 standard from 2005 titled Occupational and Health and Safety Manage-ment Systems must be followed to evaluate risk poten-tials throughout all modes and operations of a given machine. In addition, ANSI PMMI B155 2006 and S2for the semiconductor industry to mention a few, have been updated to more clearly call out the risk assess-ment requirement and reference other standards for more detailed information.

The risk assessment process iden-tifies risk levels that could injure the operator, maintenance personnel or even individuals walking past a machine. The person conducting the risk assessment must be trained, and understand how machinery opera-tion and production is affected by applicable codes and standards.

By evaluating the machine and the environment around it for safety, a risk assessment lets a manufacturer know what needs to be changed to meet applicable codes. It also significantly lowers the risk to machine operators. If an injury occurs, OSHA will ask what the employer has done to make the area safe. A risk assessment shows

the employer has taken steps to understand and correct any associated standard violations.

Looking beyond the factory doors and into the global marketplace, OEMs and machine builders know that machines shipped to Europe are required to have com-plete risk assessment documentation.

Safety optionsThe right safety strat-

egy can provide a com-petitive advantage for the manufacturer. The recent changes in safety standards have opened the door to new solutions that would not have been per-mitted under the old rules.

Choosing the right option can result in a quicker time-to-market with higher product throughput, and a lower total cost of ownership for safety systems, improving both overall equipment effectiveness and return on assets.

Safety options to consider include:Dedicated safety relays: The mainstay of safety cir-

cuits for decades, dedicated safety relays continue to be

Networked safety relays may not be the best solution for highly complex systems where minimizing control programming is required.

Functionality vs. product cost

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Although it’s not the least expensive option, integrated safety PLC systems offer a comparitively high functionality to product cost ratio.

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used even today. However, while dedicated safety relays may help meet machine safety standards, the overall costs may outweigh the benefits. These relays significantly limit the ability to monitor and troubleshoot machines. For example, a single machine might incorporate 20

emergency-stop buttons – any one of which must shut it down. Traditionally, E-stops are wired in series to decrease wiring cost. The challenge comes when a fault occurs and the operator needs to detect the problem. Using this conventional wiring method, many manu-facturers often spend 10 to 20 minutes diagnosing the problem on the machine.

Also, many operators using machines that rely on this configuration often bypass the safety relays with short pieces of wire so that opening the cage door or break-ing the beam on the light curtain will not shut down the machine. They claim this action increases efficiency while minimizing downtime because a maintenance person can get to the machine much more quickly and work on it even if it is still running. Despite the perceived advantages of this bypass process, this “jumpering” pro-duces a dangerous condition and a major safety violation.

Newer solutions cannot be jumpered in this manner, and therefore provide an extra level of safety.

Networked safety relays: These devices can signifi-cantly lower the cost of single- and multi-zone applica-tions by allowing one device to be wired to the entire safety circuit, providing networking to each individual device. This configuration significantly lowers the cost of wiring, allows individual safety incidents to be moni-tored and permits fast troubleshooting. It is also a very good solution for safety systems with relatively low complexity (controlling two or three safety zones, for example).

However, networked safety relays may not be the best solution for highly complex systems where minimiz-ing control programming is required. For example, an ASIsafe network offers hundreds of device options that can be cost effectively networked for safety control and monitoring.

Dedicated safety PLC: When a PLC is already in place and controlling a machine, a safety PLC may be added to the system to provide any additional safety functionality. This approach can add greater monitoring capabilities to the system if the safety PLC is networked to the control PLC and uses the existing PLC program. However, chal-lenges with this solution are the new expense when a safety PLC is added to the system, and the introduction of another programming language to learn, implement, troubleshoot and maintain.

Integrated, simplified safety system: Combining the

Overall cost savings on a standard OEM machine

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In a recent study, significant savings were identified when new and old methods of safety and automation system implementation were compared. The study explored hardware design, software design, hardware costs, build and assembly and field wiring. The chart indicates savings in every major area, delivering more than 42% net savings for the automation and safety implementation on each machine built.

This built-in safety greatly reduces cost, requires less time to implement and increases machine uptime.

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Reprinted from Plant Engineering, August 2008. Copyright © Reed Business Information, a division of Reed Elsevier, Inc. All rights reserved.Page layout as originally published in Plant Engineering has been modified.

#1-24976161 Reprinted by The YGS Group, 717.399.1900. For more information visit www.theYGSgroup.com/reprints.

functionality of a control system and a safety system into one PLC allows manufacturers to greatly reduce life cycle costs on a machine. For example, the latest safety PLCs combine integrated control and safety into one controller. Already implemented in many applications, manufacturers are saving millions in overall costs. The integrated safety system allows data to flow to the HMI for fast and easy troubleshooting. This approach simpli-fies machine control and safety system coordination from design, to installation, to troubleshooting.

Design and implementation are simplified by using the same programming language for control and safety circuits. Wiring is simplified by using safety networks to monitor and/or control each device on the safety cir-cuit. Troubleshooting is often cut by 60% to 80% since each networked device communicates via the same HMI. These advantages significantly reduce downtime and the costs associated with failures.

An integrated safety system also makes it nearly impos-sible to bypass the safety circuit by jumpering out a safety device – including a door switch or light curtain.

Integrated safety saves life-cycle costsWhen considering the right safety option for the

application, take into account the entire life-cycle cost of the product or system – not just the purchase price. Considerations include:

Design: How much design time can be saved by implementing networked safety and control into one system? Mechanical, electrical and programming issues are greatly simplified with a single PLC.

Wiring: Installing an integrated system costs far less than hardwiring. By transporting safety and regular pro-duction data on a single network (such as ASIsafe or PROFIBUS), this architecture requires the use of only

one cable instead of hundreds, or thousands, of wires and connections.

According to the electrical project engineer for a pack-aging machine manufacturer, a more complex, discrete-wired machine can take six electricians more than 368 hours to wire and start up. Integrating distributed I/O and safety I/O eliminates manufacturing redundancy and reduces complexity. Typically, two electricians can wire that version of the system in just 96 hours.

Manufacturers can now integrate electronic and pro-grammable safety systems directly into servo drives, permitting axis movement at safe speeds while an opera-tor is in the working envelope. This change reduces the number of cables and connections further – again reducing safety system complexity and lowering design, commissioning and installation costs.

Unless a machine employs only one or two safety relays, a networked safety system using a single PLC will deliver far greater benefits than traditional, hardwired methods.

J.B. Titus is a senior safety consultant and safety prod-uct specialist with Siemens Energy & Automation in Norcross, GA. Since starting with SE&A in 2003, he has organized and launched the safety initiative and business focus for the U.S. discrete manufacturing markets. He has also consulted with clients over the past 25 years regarding machine functional safety compliance. Titus holds a BBA from Oklahoma University in Industrial Management and an MBA from Case Western Reserve University in marketing and finance. He is a professional member and Certified Safety Professional (CSP) of ASSE and is OSHA-certified in machine guarding. Titus also serves on several ANSI, NFPA and NEMA national safety and health standards committees.

August 2008 Covering control, instrumentation, and automation systems worldwide

Vol. 55 No. 8

Posted from Control Engineering, August 2008. Copyright © Reed Business Information, a division of Reed Elsevier, Inc. All rights reserved.Page layout as originally published in Control Engineering has been modified.

#1-24973263 Managed by The YGS Group, 717.399.1900. For more information visit www.theYGSgroup.com/reprints.

10 ● AUGUST 2008 CONTROL ENGINEERING ● www.controleng.com

The Simatic ET 200S IM151-8 PN/DP CPU module from Siemens Energy & Automation Inc. adds another CPU to the company’s ET 200S I/O family of distributed I/O devices. Communicating via Profinet, the new CPU

is similar in power and performance to Siemens’ S7-300 line of controllers.

The built-in Profinet communication interface includes three ports for linear bus topologies and programming device functions. Communications can also be expanded with a Profibus DP master module. As a Profinet I/O controller, the inter-face module also supports the real-time properties known as RT (Real Time) and IRT (Isochronous Real Time), and can control up to 128 I/O devices.

The built-in Web server function allows simple access to both hardware and controller diagnostics and mes-saging information via the Internet or intranet from any remote location using a standard Internet browser. A Web server function requires no programming or special software on the remote end, and works with any type of Web client such as a PC, multi-panel or PDA.

A fail-safe version is also available with a built in Pro-

fisafe safety network. The CPU can be expanded modularly in a central rack configuration or distributed via Profisafe on Eth-ernet for combined standard and safety-rated applications. This modular safety system is certified for use in applications up to SIL 3 in accordance with IEC 61508, 1999, for use up to SIL 3 in accordance with EN 62061, 2005, and for use up to CAT4 / PL e in accordance with ISO 13849-1, 2006. www.sea.siemens.com

Distributed controller has Profinet

EXCLUSIVEproduct

Siemens distributed I/O controller features a built-in Profinet interface with three ports for linear bus topologies and programming device functions.

ctl0808pe_ID.indd 10 9/19/08 7:32:52 AM

Answers for industry.

See for yourself how flexible and efficient integrated safety can be. SIRIUS MSS, the new modular and software-parameterizable safety system, is our latest expansion of our comprehensive safety technology portfolio. Benefit from this integrated and safe platform for your machine and system availability. Advantages include modular flexibility and communication capabilities to higher level control systems. Cost savings are realized with the fast and easy parameterization MSS ES software. More information: www.siemens.com/sirius-mssSetting standards with Totally Integrated Automation.

Safety Integrated

Simplify Wiring of Multiple Safety Functions...

… and Opt for Easy Parameterization with the SIRIUS 3RK3 Modular Safety System

10 ● AUGUST 2008 CONTROL ENGINEERING ● www.controleng.com

The Simatic ET 200S IM151-8 PN/DP CPU module from Siemens Energy & Automation Inc. adds another CPU to the company’s ET 200S I/O family of distributed I/O devices. Communicating via Profinet, the new CPU

is similar in power and performance to Siemens’ S7-300 line of controllers.

The built-in Profinet communication interface includes three ports for linear bus topologies and programming device functions. Communications can also be expanded with a Profibus DP master module. As a Profinet I/O controller, the inter-face module also supports the real-time properties known as RT (Real Time) and IRT (Isochronous Real Time), and can control up to 128 I/O devices.

The built-in Web server function allows simple access to both hardware and controller diagnostics and mes-saging information via the Internet or intranet from any remote location using a standard Internet browser. A Web server function requires no programming or special software on the remote end, and works with any type of Web client such as a PC, multi-panel or PDA.

A fail-safe version is also available with a built in Pro-

fisafe safety network. The CPU can be expanded modularly in a central rack configuration or distributed via Profisafe on Eth-ernet for combined standard and safety-rated applications. This modular safety system is certified for use in applications up to SIL 3 in accordance with IEC 61508, 1999, for use up to SIL 3 in accordance with EN 62061, 2005, and for use up to CAT4 / PL e in accordance with ISO 13849-1, 2006. www.sea.siemens.com

Distributed controller has Profinet

EXCLUSIVEproduct

Siemens distributed I/O controller features a built-in Profinet interface with three ports for linear bus topologies and programming device functions.

ctl0808pe_ID.indd 10 9/19/08 7:32:52 AM

Answers for industry.

See for yourself how flexible and efficient integrated safety can be. SIRIUS MSS, the new modular and software-parameterizable safety system, is our latest expansion of our comprehensive safety technology portfolio. Benefit from this integrated and safe platform for your machine and system availability. Advantages include modular flexibility and communication capabilities to higher level control systems. Cost savings are realized with the fast and easy parameterization MSS ES software. More information: www.siemens.com/sirius-mssSetting standards with Totally Integrated Automation.

Safety Integrated

Simplify Wiring of Multiple Safety Functions...

… and Opt for Easy Parameterization with the SIRIUS 3RK3 Modular Safety System