Ian Verhappen, P.Eng.
Ian Verhappen, P.Eng. is an ISA Fellow, ISA Certified Automation Professional, and a recognized authority on Foundation Fieldbus and industrial communications technologies. Verhappen leads global consultancy Industrial Automation Networks Inc., specializing in field level industrial communications, process analytics and heavy oil / oil sands automation.
The industrial networking environment is continuing to evolve with additions to protocols, new tools and, with the Field Device Initiative (FDI), even amalgamation to some extent. However all the ‘buzz’ continues to be about wireless and cybersecurity, which is relevant regardless of the network you are operating.
Many of us forget that cybersecurity is about more than the network but starts with policy, procedures and physical access. With wireless, physical access includes managing your wireless footprint. This includes such things as the power levels of your transmitters and gateways as well as, if used, the associated antennas.
There are a number of open source tools to help you manage the footprint of your wireless network including:
• Netstumbler (Netstumbler.com), one of the original wireless network tools that was often used by hackers to find networks while roving.
• Netsurveyor (www.performancewifi.net/performance-wifi/main/NetSurveyor.htm), which is similar to Netstumbler but also has a recording/playback feature and comes with ‘add ins’ such as NetStress, which is a comparison tool to see how your network is doing over time.
• CommView for WiFi, which allows you to capture packets and then search them for specific strings and packet types. This is the wireless version of Wireshark (wireshark.org) for wired networks which, rather than gathering data on the network layer, allows you to diagnose problems in other layers as well.
• inSSIDer from Metageek (www.metageek.net/products/inssider/), which is similar to Net Stumbler and is designed to detect wireless networks and report on their type, maximum transfer rate and channel usage. InSSIDer includes graphical representation of each wireless network’s amplitude and channel usage
• Azulstar developed Wireless Wizard (www.azulstar.com/support/wireless-wizard/) to provide a series of diagnostic tests to see how well your wireless network is performing. More commonly used on ‘the home front,’ it also includes a spectrum analyzer that recommends the best wireless channel to use.
Staying with the “Open Source” concept, there is also an “Open source” antenna, or cantenna as it is affectionately known, with instructions available from a number of web sites. The cantenna was the created in July 2001 from an empty Pringles chips can and hence the name. The cantenna is a directional 2.4 Ghz wireless network 12dB yagi antenna, with a collector rod assembly, compatible with 802.11b and 802.11g wireless networks.
Open source is also coming to our assistance on the cybersecurity side with a test suite from the Open Information Security Foundation (OISF). OISF has created an Open Source Intrusion Detection and Prevention Engine called Suricata. The United States Department of Homeland Security’s Directorate funds Suricata for its Science and Technology HOST (Homeland Open Security Technology) program, the U.S. Navy’s Space and Naval Warfare Systems Command (SPAWAR) and other consortium members.
The Suricata Engine and the HTP Library, an HTTP normalizer and parser written by Ivan Ristic of Mod Security are available to use under GNU General Public License (GNU GPL) version 2. The HTP library is required by the engine integrates and provides very advanced processing of HTTP (Hyper Text Transfer Protocol – the same protocol used to read/display web pages) streams for Suricata. Suricata is available for download at www.openinfosecfoundation.org/index.php/download-suricata.
One more tool to help you manage your network is Network Diagnostic Tool (NDT) (www.internet2.edu/performance/ndt/) which is designed to quickly and easily identify a specific set of conditions that are known to impact network performance. NDT does this by performing the following tasks: simple bi-directional test to gather E2E (End To End) data; gather multiple data variables from the server; compare measured performance to analytical values; and then translate network values into plain text messages for interpretation by yourself or your network administrator.
This article originally appeared in the May 2013 issue of Manufacturing AUTOMATION.
All of us are aware of the amount of data available from modern control systems, their field devices and the algorithms used to infer additional information from that data. The challenge is managing and understanding that data by converting it first into information that we as humans can understand, and then into knowledge upon which we can take appropriate actions.
We have learned a lot about how to display data since the introduction of the DCS and computer displays in the 1970s, when the display was a colour version of the Piping & Instrumentation Diagram (P&ID) with key process values shown numerically and electronic versions of strip charts to allow operators to observe process trends. We then “progressed” to Windows-based HMIs with even more distractions of spinning pump impellers, fluidized beds and all the wizardry of computer gaming at that time. Fortunately, research has shown simplicity and low-key use of colour is better, with this information being codified in the work of two ISA standards committees: ISA18—Instrument Signals and Alarms and ISA101—Human Machine Interfaces.
From its purpose and scope on the ISA web site, the ISA18 committee “develops standards, technical reports and guidelines for alarm systems including annunciators, process automation systems and the general development, design, installation and management of alarm systems in the process industries. They do so by establishing terminology and practices for alarm systems, including the definition, design, installation, operation, maintenance and modification and work processes recommended to effectively maintain an alarm system over time.”
In addition to updating the 2004 revision of the ISA18.1 standard on ‘Annunciator Sequences and Specifications,’ it is focused on the development of a series of technical reports on ‘Management of Alarm Systems for the Process Industries’ as part of the ISA18.02 standard set.
Each of the six working groups are developing reports as follows:
• WG1—Alarm Philosophy: Provides guidance for successful management of the alarm system. The resulting work will cover the definitions, principles and activities by providing overall guidance on methods for alarm identification, rationalization, classification, prioritization, monitoring, management of change and audit.
• WG2—Alarm Identification and Rationalization: Addresses the processes to determine the possible need for an alarm or a change to an alarm, systematically compare alarms to the alarm philosophy and determine the alarm setpoint, consequence, operator action, priority and class. To accomplish this work, the resulting outputs will address the identification, justification, prioritization, classification and associated required documentation for the creation and maintenance of individual alarms and associated support systems.
• WG3—Basic Alarm Design: Covers the selection of alarm attributes such as types of alarms, deadbands and delay times. Because each control system has different capabilities with respect to alarms, the resulting implementation of this work may be specific to each control system.
• WG4—Enhanced and Advanced Alarm Methods: Will provide guidance on additional logic, programming, or modeling used to modify alarm behaviour. The resulting tools to support advanced alarm methods will likely include dynamic alarming, state-based alarming, adaptive alarms, logic-based alarming, predictive alarming, as well as a number of approaches to logically implement designed suppression of redundant and condition-based alarms.
• WG5—Alarm Monitoring, Assessment and Audit: Focuses on monitoring, assessment and audit for the continuous monitoring, periodic performance assessment and recurring audit of the alarm system to keep system and operator performance from deteriorating over time. Fortunately, many modern alarm systems contain the tools to assist in this activity already.
• WG6—Alarm Design for Batch and Discrete Processes: Providing guidance on the application of alarm design of batch and discrete processes.
Similar to ISA18, the ISA101 committee’s purpose and scope are to establish standards, recommended practices and/or technical reports pertaining to human-machine interfaces in all manufacturing industry applications.
The areas covered within ISA101’s work will include: menu hierarchies, screen navigation conventions, graphics and colour conventions, dynamic elements, alarming conventions, security methods and electronic signature attributes, interfaces with background programming and historical databases, popup conventions, help screens and methods used to work with alarms, program object interfaces and configuration interfaces to databases, servers and networks.
As you can see from the above there is significant activity underway to ensure that we will be able to properly manage the plethora of data available in today’s control systems. The one thing that modern HMI and operator interfaces, both in the control room and on smaller devices, are doing is helping us to make informed decisions faster, less stressfully and with less chance for error.
This article originally appeared in the March/April 2013 issue of Manufacturing AUTOMATION.
As a chemical engineer who graduated 30 years ago, I know that other than the basic skills I learned at university (which formed the platform on which I was able to develop a career) much of what I do today was learned post graduation.
Fortunately, the basic theories of physics, chemistry, etc., do not change and that forms the foundation, just like our education prior to entering post secondary studies forms the foundation on which our fields of specialization reside—it’s one big pyramid.
This pyramid is why we need to develop the next generation of technical folks today. If we don’t, not only will we not be able to retire, but our country’s economy will also pay the price.
But the time to get young people interested is NOT when they are about to graduate. Instead, we must reach them between grade 7 and grade 9, because that is when they will have a reason to do well in the core subjects necessary to become the next generation of technologists.
One way that we can all help is to become involved locally by mentoring young people and showing them that, despite being engineers, we are “real people.” Some obvious examples of good fits are FIRST (www.usfirst.org) and the better-known Lego League (with whom ISA has created a partnership), coaching a local sports team, mentoring, or any other way of interacting with young people so they can ask, “What do you do?”
Once someone has an interest in joining our exciting field of work, there are many opportunities for post-secondary development. In addition, we are fortunate to have an effective apprenticeship program here in Canada. However, as stated at the start of this column, once we have our degree is when we really start our education—learning not only ‘hard’ technical skills but also the important ‘soft’ people skills.
A common way of learning new skills, other than reading appropriate journals, is to participate in technical society meetings such as IEEE, ISA, PMM, etc. This is how I continued to develop my skills for much of my career and the following story pretty well summarizes the result.
When I entered the process analyzer business in the late ‘80s and went to ISA Analysis Division meetings, I was the “young guy” (only being in my early 30s). Everyone else was 20 years my senior, so they were happy to see someone behind them preparing to pick up the baton. Now I am the person looking behind me for someone to pick up my baton when I am ready to slow down and it does not look promising.
Another way to not only stay on top of developing technology but also to influence it is by participating in standards development activities. Here in Canada, doing so is free and can typically be done through the appropriate sponsoring Standards Developing Organization (SDO) such as CSA, ISA, IEEE, or directly through the Standards Council of Canada (SCC). If you are interested in learning how to participate in SCC or ISA, where I am active, please contact me directly and we will get you started. One of the conditions of becoming an ANSI accredited SDO is that membership must NOT be a prerequisite to participation so you can join any ISA or IEEE standards committee without having to pay annual dues.
Automation is unique in that there are few universities around the world that truly teach automation. Many teach process control, but that is not the same as the learning about the devices that actually connect to the process—all the more reason that we need to mentor new graduates and stay current ourselves.
Just like the technology on which we rely as automation professionals continues to evolve, so too must we continue to grow and develop our skills to not only remain relevant to our employers but also to remain competitive ourselves. Investing in yourself will always provide returns in self satisfaction.
This article originally appeared in the January/February 2013 issue of Manufacturing AUTOMATION.
IEC TC65 and its subcommittees are responsible for preparing “international standards for systems and elements used for industrial-process measurement and control concerning continuous and batch processes.”
There are four subcommittees within TC 65: SC65A, dealing predominantly with safety-related items; SC65B, covering instrumentation and analyzers; SC65C, looking at communications and networks including industrial wireless; and SC65E, examining the specification of digital representation of devices. There are also a number of Working Groups responsible for such items as cybersecurity and Joint Working Groups that cooperate between different IEC and ISO committees.
The IEC “65” committees met the week before and after ISA Automation Week in Orlando to continue their work and have a plenary meeting. This plenary meeting is held every 18 months where the various oversight boards of “65” meet to review the status of existing and planned work items or standards. Canada is represented at the IEC by our mirror committees operated through the Standards Council of Canada. Here are some of the highlights from these meetings that could have an impact on you and your work as a Canadian engineer.
In SC65A, the Maintenance Team (MT) for IEC/ISO 61508 parts 1, 2, 4, 5, 6 and 7 reported that an enhanced (or augmented) version of IEC/ISO 61508 with mark-ups and hyperlinks that provides additional text to support the implementation of the existing IEC/ISO 61508 is available for sale from the IEC website.
As the current IEC/ISO 61508 standard does not address human factor issues, the ad-hoc group on human factors and functional safety recommends the establishment of a working group to add the required material, and they have identified an existing U.K. document as a good starting source for this information.
With the increasing use of smart transmitters, SC65B will be revising IEC 60770-3 “Methods for performance evaluation of intelligent transmitters,” which is starting its regular maintenance cycle to reflect these changes. The committee is working with European End User Groups CLUI and EXERA who are providing input to the proposed changes.
Similarly, IEC 62828, “Requirements and tests for industrial measurement transmitters,” is to be updated to incorporate digital capabilities of modern transmitters and will be created as a new series of documents for pneumatic, analogue, digital, etc. Lastly, France is preparing a potential proposal submittal of a “Software for standard application” work item.
IEC 62603, “Industrial process control systems - Guidelines for evaluating the performance of process control systems,” will be released as a technical report for this revision, with plans to move to a full specification in three years.
The analyzer side of SC65B is working on the following document of interest to all of us because it could affect our pocketbooks: IEC 62723 Ed 1.0 “Sampling and conditioning natural gas for custody transfer analysis.” This could have an impact on the international standard for how samples are to be made for payment of natural gas which is measured in volume but paid for in energy units based on the sample analysis.
Series of standards on analyzer houses are in development that will improve the reliability of analyzer sample systems. As Canada has a number of experts in this area we should contribute to these documents which at present are being driven by NAMUR from Germany.
SC65C, which includes the wireless standards where ISA100.11a is presently in ballot with a planned draft standard release in Q1 2013, also reported on the status of the 52 documents they oversee including 25 fieldbus documents, 27 Ethernet documents and nine fieldbus safety profiles.
The final group, SC65E, is home to the various ‘languages’ and protocols for device communication and FDI (Field Device Interface), and will issue a draft ballot in March 2013 and five related new work proposals for H1, HSE, Profibus, Profinet and HART protocols. In addition, IEC 61804-1 will be withdrawn by January.
The largest work piece underway within SC65E JWG 17, Lists of Properties (LOP) for automated valves and process regulators (SC65B/WG9 and SC65E/WG2), is generating Operating Lists of Properties (OLOP) and Device Lists of Properties (DLOP) for automated industrial valves (including control valves and process regulators) and their components as well as the characterization for this device family. When implemented, this will have significant impact on the way we work because the List Of Properties standards are defining all the parameters associated with the life cycle of a field device in a database format which will replace data sheets and allow for the ordering, repair and disposition of any field device within this single environment.
A relatively new IECEE CB-scheme creates an Industrial Automation (INDAT) category that means industrial automation equipment certified by an IEC-subscribing nation can be accepted worldwide. It is therefore important that with a U.S. approval agency participating and supporting the resulting standards, Canada must participate in the development of IEC 61010-2-201 which is the first document to use INDAT on electrical safety of industrial control equipment.
Many of us take standards for granted, however, as we all know, they do have a significant impact on our lives and work. Therefore, if you feel that you have some expertise in the area of automation and control and an interest in participating in the IEC standards activity on behalf of Canada, please let me know and I will be sure to forward your information on to the SCC and the appropriate committee.
This article originally appeared in the November/December issue of Manufacturing AUTOMATION.
An estimated one-third of maintenance expenditures are wasted due to improper or unnecessary practices. According to a report issued by the E.I. duPont de Nemours Company, “The largest single controllable expenditure in a plant today is maintenance, and in many plants the maintenance budget exceeds annual net profit.”
Maintenance averages 14 per cent of the cost of goods sold in many industries, making it a prime target for cost reduction efforts. Traditional belt tightening and budget slashing can negatively affect quality, productivity and employee morale. A better solution is using emerging technologies such as smart instruments and Plant Asset Management (PAM) systems designed to streamline maintenance practices and reduce waste.
It is common for control systems to be significantly under-performing, with more than half of all control loops showing some form of serious performance issue.
Intelligent or smart instruments are those that have self-diagnostic capability, either for a complete analysis or a simple checkup, depending on the manufacturer. They have sensors to monitor and send information to the microprocessor that uses special firmware to indicate the instrument’s condition and, in the event of failure or calibration deviation, send this information to the interfaces managing the system.
Unfortunately, it is estimated that as many as 85 per cent of the 25 million most common “smart instruments” in use (a HART device) cannot directly connect digital data to systems that manage, monitor and control industrial plants. Each of these HART-enabled devices contains 35-40 data items that can be used to improve the performance of an industrial plant.
A large part of the reason all this data is stranded is that data is often isolated as “islands” because of the need to convert data from one format or system to another via middleware. Unfortunately, it is the management of all the data flowing back and forth between the different components of control system, maintenance system and enterprise resource planning / scheduling software that are the keys to success. Doing so has traditionally required building custom bridges.
These data, associated with the self-diagnostic of the instruments, make proactive maintenance possible. The operational statistics predict the degradation of the devices liable to cause imperfections or failures and can be used to reduce the process variability to determine if/when the device needs immediate fixing. By comparing the data from the manufacturer and site history, this information may be used to estimate when the device may fail, determine the state of the device in its instrument life cycle and discover the operational condition of its critical parts. Operational statistics are data stored in the instrument to inform how much it has been used; or how many times a specific or an abnormal condition occurred.
To be able to access the information in these smart devices, the system must support Electronic Device Description Language (EDDL) and Field Device Tool / Device Type Manger (FDT/DTM) technology for the efficient, convenient configuration and diagnosis of Foundation fieldbus, HART, Profibus PA, Profibus DP and DeviceNet field devices.
New, integrated on-line condition monitoring and protection systems can now significantly increase production throughput by communicating directly with control system field devices via the controller I/O cards the existing control network architecture without proprietary racks or networks.
When online monitoring of device alerts is interfaced with an Enterprise Asset Management system, users are automatically notified if a device needs maintenance and work orders are immediately generated. The work order usually includes the ID number of the device, its priority and its location in the plant.
Of importance for interoperability is the use of open standards regarding syntax and semantics for the information exchange between engineering control systems. In addition to the use of standardized communication protocols, the consistency of the structure and importance of information in particular are crucial in this context.
Advanced (PAM) systems include inputs from process control data historians and include sophisticated state-aware condition monitoring technology – automatically setting multiple “baselines” for equipment based on variable operating loads, speeds and other process conditions. This allows the system to be sensitive to the current operational “state” so as not to over-alarm or under-alarm.
The purpose of a PAM system is to provide timely information about developing faults in a wide range of critical plant assets to operations and maintenance (O&M) personnel so that corrective actions can be taken before production is impacted or before safety is compromised.
The net result is that by using all the data available to them, maintenance personnel can use the predictive information sent from the PAM system to develop optimized schedules based upon the actual asset condition instead of the manufacturers’ recommended PM interval and, in the process, significantly lower overall operating costs with each dollar saved going straight to “the bottom line.”
In many applications, there is a critical need to monitor moving parts, thus requiring cable-free, wireless operation. For example, wireless sensors are highly effective at observing and controlling moving objects in high temperature zone furnaces or rotating rotors and blades at high accelerations.
Meeting the need for developing associated low cost, low power, wireless sensors to achieve the required degree of surveillance in other environments and applications will require new sensing technology. Passive wireless sensors are just one of the options in the “tool box” for reducing dependency on wired connectivity and adding functionality without wires or cables.
Two passive wireless sensor technology options are viable alternatives: active RFID sensor, wherein a reader broadcasts induced power to the sensor/transmitter system, which acquires the sensor data and sends that data back to the reader; or a system that is powered via a custom thin film thermal electric generator and can be used to measure parameters such as vibration, pressure, temperature and others. The peak power dissipation for the whole chip, including memory, logic and transceiver stage, is 2uW. The low power makes it possible for the chip to run on many sources of ambient energy at extremely low cost and small size.
Passive wireless sensing technology measures physical properties using unpowered surface acoustic wave (SAW) devices and radio frequency (RF) interrogation techniques. Very few sensor systems exist that can provide reliable operation at temperatures in the 500 degrees Celsius to 1000 degrees Celsius range, pressures up to 750 psi, and in highly reactive, explosive and/or toxic gas environments. SAW sensors can already be used up to 400 degrees Celsius (752 degrees Fahrenheit) for measuring temperature, pressure, force or strain. In the near future these sensors will be able to stand temperatures up to 600 degrees Celsius (1112 degrees Fahrenheit) and comply with 433MHz standards.
Commercially available systems today are:
• Passive, battery-free, lightweight, harsh environment wireless microwave acoustic sensors and sensor arrays; these have a small footprint and around a gram in weight depending on the application;
• Stable, medium and long term (>1000 hrs);
• Operate under severe thermal shock conditions (room temperature to >700 degrees Celsius within a few seconds);
• Survive g-forces in excess of 50,000g on rotating parts;
• Use sensor arrays to operate simultaneously in groups of eight or more while retaining the ability to individually identify and read each sensor for pressure, strain and vibration measurements;
• Contain stored data that can be retrieved and changed with remote/non-contact means;
• Provide location and range information (passive tags can be located with 5-8 centimeters of accuracy within a range of 100 metres), and;
• Operate at either low power short range or high power long range.
Turbine engines, power plants and oil/gas extraction machinery are examples of harsh environment applications that require and will significantly profit from high-performance wireless sensor systems. A class of wireless sensors have been developed that address the operational environment using passive, RFID-like sensors that can be deposited on turbine blades or other surfaces and offer long term, reliable operation. This RF circuitry is “printed” on the surface similar to the processes used to make integrated circuits, and their mass and size are sufficiently small so that they do not alter the vibrational modes of the blade on which they are mounted. They are totally passive, requiring no external power to operate. They operate by receiving an interrogating signal, modulating it with the parameter value being monitored, and re-transmitting the modulated return signal to a receiver/signal processor for measured parameter estimation.
As you can imagine, there are a number of RF issues that arise from measuring strain inside an operating jet engine fan or compressor ring. In an operating turbine, multiple reflections (“multi-path signal propagation”) and Doppler shifting of the RF signals occurs along the many propagation paths, so that the RF signals to/from the sensor are corrupted and/or modulated. This situation presents a challenge for the passive wireless sensor system design that has now been overcome with the latest generation systems.
Passive sensor technology is not only being used in what is considered cutting-edge industries, but also in the more mundane ground-based transportation infrastructure. The U.S. Federal Highway Administration is investigating the use of wireless sensor system technologies to monitor structure responses at various extreme events (earthquakes, wind, scour, or other impacts). These programs are used to plan or practise emergency planning on post-extreme events, for seismic retrofitting projects and prioritizing retrofitting needs. As wireless sensor systems become inexpensive they can easily be installed on existing structures or new structures for monitoring structure during actual incidents such as an earthquake and thus provide data on how to make them safer in the future.
This article originally appeared in the September 2012 issue of Manufacturing AUTOMATION.
Networks are the infrastructure used to get the data from one node to another, while communications includes the language (protocol) so that once the message gets to the intended recipient they can “translate” all of the ones and zeros to something understandable and usable by the two devices.
Of course, as stated in the past, the network itself must be properly designed and working in order for the ones and zeros to get between its various nodes. The protocol stack determines how, when and to whom the messages are sent.
Just as we have different languages and even dialects within languages, there are also many industrial protocols available to meet the different needs of different industries — each of which have unique requirements. There are presently 19 different protocols in the IEC fieldbus standard, each meeting the needs of one or more industries.
Profibus recognizes the needs of different industries within its family of protocols; not only at the field or serial level of Profibus DP and PA, but also with its different Ethernet variants, including IRT, with a custom stack for nanosecond resolution of, for example, multi-axis machines. The field level or serial versions of Profibus all communicate with their host using the DP protocol, as Profibus PA does not connect directly, but rather through a PA/DP gateway.
Profibus PA, being designed for the process industries, follows very similar rules as Foundation Fieldbus, operating at 31.25 kbit/s and a maximum cable length of 1,400 metres with power and data over the single pair.
There are, of course, other protocols for other industries such as BACnet and Lonworks in building automation and CAN in automobiles — each designed to meet the needs of the industry for which they will be used. However, if no other option is available, a single fieldbus protocol could be made to work for every industry and application.
The majority of the buses have an Ethernet version that fortunately, because they follow the OSI seven-layer model, use the same underlying language despite the medium by which the packet or data is carried. The fieldbus packet is much like a sea container in that the data/message can be transmitted several different ways without a concern or alteration to the contents of the container/packet. This shows, once again, that just like we can use Ethernet or the telephone to carry a wide range of data types, messages or languages, the same is true for industrial protocols.
If there were only one protocol, it would be like building a house with only a hammer, which as we know means everything is a nail. However, not only is there a variety of nails to suit the task at hand, there is also a range of hammers as well.
Yes, the network is important; however, what really drives the decision in determining the correct protocol for your project is the application. Each protocol has been designed to work best in a few applications/industries, which means that you as an engineer will have to decide which tool is best suited to your project.
This column originally appeared in the June 2012 issue of Manufacturing AUTOMATION.
The reality is that remote I/O, wireless access points and similar equipment are typically mounted in Class I Division 2 (Zone 2) classified areas.
So why are there so few options on the market that meet the requirements for reliable field mounting? First, I should explain what I feel a reliable field-mounted power supply should contain, besides, of course, the AC or 24 VDC power:
• Redundancy. The power supply should be redundant so that if one unit fails, there is no interruption in the output. As is done with most Foundation Fieldbus power supplies, this will likely mean a load-sharing configuration sized for 120 percent or better of load to handle surges during switch over and while repairs are being made.
• Separate mains. Each of the power supplies should be fed from two separate mains. The majority of larger facilities have an A and B bus in the plant so that maintenance can be done on the electrical system without requiring a full plant outage.
• Minimal points of failure. To provide the highest level of reliability, there should be minimal single points of failure, so the backplane for the units should not have any active components that could possibly fail. Any electronics should be mounted on pluggable modules that reside on this passive backplane so that they can be both easily serviced and upgraded in the future.
• Component failure. Some form of component failure needs to be included that can annunciate both locally and remotely via the control system. The remote indication can be either a single contact, a fieldbus signal or a wireless transmission to the DCS.
• UPS capability. The system should have UPS capability to not only clean up any noise in the resulting power output, but also to provide time for the components being powered from this supply to fail in a graceful manner, or at least give the operators time to take the appropriate action. Of course with the redundancy above, the batteries for the UPS will not be stressed too often, so the system should also include some way of testing them on a regular basis.
I am aware of only two options that meet the majority of these requirements — one from Weidmueller and the other from Phoenix Contact. The only reason I can think of for this limited number of options is that, until recently, there have not been sufficient potential applications to justify the development costs. It’s also possible that there are more products that exist, but that they are hidden in the product line.
Power over Ethernet (PoE)
An alternative to the field-mountable power supply is PoE, which can now generate a maximum of 56 watts of power at 40 VDC. Unfortunately, Ethernet is limited to distances of 100 metres, so in some cases, this will not be enough. Fortunately, most home run cables in a typical plant are just over 100 metres, so with careful planning this may be feasible. Alternately, if manufacturers were to make an Ethernet cable with larger wire size to reduce resistance, it may be possible to get longer distances.
Having a field-mountable power supply or a PoE-enabled product suitable for field mounting on the market not only removes the hurdle to reliable field power, but when sized properly, it also gives you sufficient time to sort out the source of other operational problems that could be occurring at the same time, since you will now be able to monitor them. Better yet, it will give you the time required to bring your facility down in a safe manner.
This column originally appeared in the May 2012 issue of Manufacturing AUTOMATION.