Though only mentioned in my last column, the Field Device Initiative (FDI) is continuing to move forward. The reason this is important is because I estimate that 95 per cent of the field devices used in the process industry are based on DD technology. HART, Profibus and Foundation Fieldbus are all based on DD technology and these groups are working with FDT and OPC to have the resulting documents out for IEC ballot as Committee Draft for Vote with the expectation for publication early next year, with products released at approximately the same time. As always, one challenge of releasing products is coordinating the timing of field devices and host systems to support the new capabilities. It is this factor that will drive the timing for use of FDI in the plant environment. Let’s have a look at what has led to the development of EDDL and just how FDI will change the way we interact with our field devices. As a declarative language, EDDL describes the capabilities of the field device, leaving it to the host system to determine how to access all data and properties of all devices. As a result, EDDL tends to be used for device configuration with limited graphical support conducive to maintenance activities. Hence, the FDT organization developed DTMs. FDT is independent from any communication protocol and the software environment of the host system. A device DTM can be used to access device parameters, configure and operate the device and diagnose problems. A second DTM, called a Gateway or CommunicationsDTM, is used to connect to the device DTM and handle protocol transformation. A key group in the development of FDT and recent additions to EDDL technology is the NAMUR organization of end user manufacturers. The recommendations in its document NE105, “Specifications for integrating fieldbus devices in engineering tools for field devices,” was one of the guiding documents identifying the requirements for FDI. So what is FDI, beyond another acronym to learn? The core of FDI technology is the scalable FDI package containing up to four different elements. The FDI package is a collection of files: The Electronic Device Description (EDD), based onElectronic Device Description Language (EDDL, IEC 61804-3), includes the device definition (Def) that serves as the information model of the device and describes the device data and type; business logic (BL) outlines the rules for accessing the device data and any dependencies and is used to define if and how the data may be viewed when interpreted by the server; and user interface description (UID). The optional user interface plugin (UIP) offers the advantages of freely programmable user interfaces based on Windows Presentation Foundation (WPF) used by FDT as software components that define special device functions/application information and user interfaces to run on the client. Attachments are also optional and include things like product manuals, images and electronic certifications. To prevent inadvertent errors, a number of safeguards are built into the protocol so that if there are EDD constructs (including built-in functions) that are not known to the FDI Server, the execution of the business logic shall be cancelled and if the FDI client’s UID Interpreter is not able to interpret and/or visualize a part of the UID, the user shall be informed that the resulting information is likely invalid. The device manufacturers define via the FDI Device Package which data, functions and user interfaces are stored on the FDI Server. This makes version management of FDI packages much easier as they are managed centrally within the FDI Server. Device packages created by device manufacturers will be certified and registered by their respective technology foundation, so it will still be best to verify the device package you are using on the relevant technology foundation approved lists on their website. Because the EDD, DTM and new FDI Package exist only on the computer, not in the device, it is possible to migrate from DTM or EDD to FDI without changing the devices, thus protecting the existing investment of your field devices. However, one of the requirements of FDI is that the major revision of all clients, servers and packages in a given system shall be the same. FDI servers support all FDI packages following the same version or lower. FDI clients can typically be connected to FDI servers that are implemented following the same FDI technology version or higher. An FDI client may access multiple devices, while User Interface Descriptions and User Interface Plug-ins may only access a single device. FDI clients can communicate with the FDI server through proprietary protocols; however, if the FDI server supports third-party FDI clients, it shall support OPC UA as well so that generic OPC UA clients with no knowledge of FDI can connect to the FDI server. The comprehensive set of services provided by OPC UA enables the “how” of system integration while the basic building blocks of the “what” of system integration are defined by OPC UA’s an extensible object model. OPC UA services act on an object model, which is managed by the server and discoverable by a client. Information is conveyed using standard and vendor-defined data types, and servers define object models that clients can dynamically discover. Though an FDI communication server can be embedded within a communication device or can be provided via a separate server, the FDI server is usually distinct from the servers that provide run-time data to the operator, engineering and maintenance stations. Though it appears that FDI will be more complicated than the EDDL we are using now, a lot of effort is being made to hide this complexity from the end user by providing an integrated graphical environment in which it will no longer be necessary to become protocol experts to keep your devices working and THAT is always a good thing—and a definite upgrade from today. This article originally appeared in the June 2013 issue of Manufacturing 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.
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.”
Although smart wireless sensor nodes and networks are coming into maturity, the cost per measurement point is still high and functionality somewhat limited, which means that there is still opportunity to improve on the economics of wireless sensor networks. As a result, most of the wireless sensing systems being installed today are for applications that are difficult due to extreme cost, scheduling issues or lack of physical access (i.e. using wired sensors with rotating components is difficult since slip rings are inherently noisy and unreliable and only a limited number of sensors can be accommodated).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.
Though the terms are often used interchangeably, there is a difference between communications and networking. 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 increase in the use of field-mounted equipment that requires a reliable power supply reinforces the need for power supply equipment and designs. Unfortunately, when I talk to companies that normally provide AC/DC converters or UPS supplies, few of them provide the option of a unit suitable for installation any place other than the confines of a nice clean interface room, or at most an unclassified area. 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.Benefits 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.
There is a lot of discussion these days about energy conservation, energy management and "going green" - for both environmental and economic reasons.
Original pneumatic process control loops were implemented with Control in the Field. In those days, the analog input (transmitter) and output (valve) needed to be connected by the air line sharing the 3-15 psi signal calibrated to the transmitter signal. As indicated in past columns, Foundation Fieldbus - with its function blocks - has been designed to be able to implement Control in the Field with the constraint that, like pneumatic loops, the input (AI block) and output (AO block) must be on the same physical segment. In effect, the pneumatic air line has to be replaced with the fieldbus segment wire.
When you talk to safety system and control engineers, many say that they do not have faith in the communications reliability of buses and prefer to use conventional analog signals for all safety applications and SIS (Safety Instrumented Systems). Why? Because, they say, conventional analog signals have been proven in use for so many years. It seems as though these engineers have conveniently forgotten that there was a time when these systems were new as well.
The majority of new electronic field devices being installed today all have some form of diagnostics capability, and most also have some way of communicating their overall general health to another system that can make use of this information to improve overall plant reliability. This reporting system is typically called an asset management system.
Networking technology has been around for at least as long as computers; however, it was not until the 1970s that the demand for permanent connection between distributed nodes became more important.
We are all familiar with the phrase "garbage in, garbage out," but how many of us realize that this statement is also true for our control systems?
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