Nowadays, product features are often what differentiate one component from another. Diagnostics and maintenance feedback functions are a major way to add value to your design, by providing a way to run processes more efficiently or produce a higher quality product. They can report output, predict the upper limits of a new design, and make maintenance more effective. “Whether new or for the retrofit market, the paybacks are huge when diagnostics are provided, employed, and used correctly,” says Don Kosnik, product manager at Avtron Manufacturing Inc., Cleveland. Diagnostics also assist in the detection of suboptimal equipment conditions. “So if a system is not monitored, then reliability and maintenance personnel have no opportunity to know the condition of the equipment,” says Howard W. Penrose, Ph.D., CMRP, president of Success by Design Reliability Services, Saybrook, Conn.
Because diagnostics is based on data processing, accurate input information is paramount to these systems. The quality of data depends heavily on the caliber of both data collection and system connectivity. Open standards such as Ethernet itself, open industrial protocols on Ethernet, OPC, HTML, ACTIVE-X, and XML have improved industrial communications in recent years. “And diagnostic information in real-time is also vitally important,” says Kosnik. It's nearly impossible to diagnose systems with information fed slowly relative to the process; timely information about a system's status provides a real picture of subtle motion workings, and allows users to make corrections more quickly. “Productivity increases with direct process control using immediate feedback,” agrees Ralph Brillhart of Advanced Test Group, San Diego.
Diagnostics can be optimized for a new system in a couple ways. “Data from existing systems and historical information can be used directly to define the environment that exists for a new system,” says Brillhart. This translates into more efficient new designs by preventing overdesign and ensuring proper parameters from the start. Too, new designs can incorporate the ability to make measurements that allow for future diagnostics — improving the new design's life, and validating design criteria — in turn, feeding improvements for future designs.
Without diagnostics, prototyping and assembly are especially inefficient. Diagnostics improve assembly by adding calibration functionalities for visibility in production and process quality, machine downtime, and synchronizing multiple production and logistics schedules. “This calibration must be frequent, consistent, and comply with process quality standards, but slow the process as little as possible,” says Jacques Hoffmann, president of InterTech Development Co., Skokie, Ill. “When systems are calibrated ineffectively, they don't reveal problems in underlying system design and functioning. So then phenomena such as leak test fixtures, for example, can allow creep that makes it impossible to differentiate good parts from defective, or system design flaws resulting in inadequate signal-to-noise ratios during electrical testing.”
On lines that run continuously, especially on critical, costly systems, regular diagnostics is the most effective way to foresee potential breakdowns. Now, in many cases, diagnostics are being built directly into new systems, right off the assembly line. “Investing in new equipment with this capability is expensive, but it promotes more effective and consistent routine maintenance,” says Rick Brooks, manager of reliability services, The Timken Co., Canton, Ohio. Systems can automatically perform diagnostics checks at scheduled intervals to report back to an online maintenance program, drastically reducing unplanned downtime for repairs. “In this way, a plant can operate on the offense rather than the defense. Otherwise, if systems do not have these diagnostics preinstalled, consistent screenings can be achieved with effort and a little diligence,” Brooks adds.
Newly installed equipment should be tested to establish baselines for future monitoring, and (by acceptance testing) to identify any faulty new equipment.
“Another benefit of consistent diagnostics testing: Improved efficiency from exposing root-cause problems, enabling engineers to correct it during design,” says Brooks.
Sometimes the final decision to include diagnostics is made by management. “Even when infrared windows and diagnostics test points are specified in the initial RFQ, they are often sacrificed to lower initial purchase cost. But in fact, this can increase safety and reliability costs over the long run,” laments Penrose. This is why the relationship between management goals and engineering realities must be clear.
Key performance indicators (KPIs) for top-level management usually relate to machine uptime, efficiency, product grade, output, or piece-count if applicable. “However, from a machine maintenance standpoint, these indicators usually are a result of other lower-level signals which must be monitored, controlled, and kept in check,” says Kosnik. For example, in continuous-web industries, a fast and very wide information channel is a must. (Wide channels feed many data points.) “Information might include speed, current, tension, draw, pressure, temperature, vibration, and position. So being able to monitor these signals allows end users to improve KPIs for management,” says Kosnik.
Even small machine efficiency increases (even 1 or 2%) can boost the bottom line of a company, paying for both diagnostic tools and the associated personnel training. At an industrial web-processing plant, for example, a typical troubleshooting call by the maintenance department might take 100 minutes. “But after the installation of diagnostic tools to monitor machine drives and PLCs, the average troubleshooting time at one plant was reduced to 10 minutes,” says Kosnik. If you look at a machine where downtime costs $6,000 to $10,000 an hour — and many troubleshooting calls can be placed in a month — diagnostics can be indispensable. “So if diagnostics are not employed, machine degradation usually occurs eventually,” Kosnik says. Machine degradation usually leads to undesirable business decisions being made. “The general value for high repair-versus-replace costs, in the USA, has averaged about $25,000 through 2006,” says Penrose.
For safety's sake
Regular diagnostics tests increase mean time between failures, increase production without capital expenditure, and reduce inventory spares and maintenance manpower. If diagnostics are not regularly performed, the consequence can be disastrous: Unplanned costly downtime, catastrophic failure, lost production, and even potential safety concerns for workers.
Improved safety can come in the form of reduced maintenance — by anticipating problems and fixing them before they happen. “The worst thing that I can imagine is loss of life as the result of a catastrophic failure,” says Brillhart. “Certainly other losses could occur as well which might result in lost productivity through downtime and repair costs. But these pale when compared to any loss of personnel. System diagnostics can serve as a warning to personnel before catastrophic events have a chance to take place,” he says. Rick West, an engineer at Sensor Developments, Orion, Mich., agrees: “When a problem goes undetected, substandard parts are created. If these parts are shipped and installed into the finished product, their failure can cause injury or death. In addition, undetected problems can lead to safety recalls, which are extremely expensive.”
It's a two-way street: Diagnostics also protect machines from humans. In built and dynamic systems, diagnostics are the only way one can differentiate good parts from bad. “And the best diagnostics do not slow down production or prototype testing, which is particularly beneficial where human intervention (and the errors normally associated with day-to-day human inputs) is removed from processes,” says Hoffmann.
Compromised processes can go unnoticed without quality benchmarks. This happens quite a bit. “For example, we often see in-process gauging stations that are insufficiently rigid or lacking correct reference points. Or with hydraulics, temperature and nonlinear compressability result in inconsistent measurements. If proper thought has been given to the real testing requirements of an application, there must be equal attention to monitoring and managing these processes and systems throughout their use — or risk product recalls, costly retesting of components, lost business and a reputation for defective products in the marketplace,” says Hoffmann.
It is better when a diagnostic system catches a problem before it becomes too expensive to fix, while preventing a machine from creating bad parts.
Is it justified?
Some say that the cost of health monitoring is an inherent cost of doing business — not something optional — and the real concern one has to consider is whether system validation methods being used are sufficiently accurate. “Indeed, more and more industrial manufacturing processes previously thought too trivial are now scrutinized … perhaps toothpicks are manufactured without too much health monitoring,” jokes West. If system health monitoring methods are themselves prone to inaccuracies, there is much reason to question whether they are worth the bother. “For example, there are still some who use mechanical calibration methods — but these methods have inherent limitations,” says Hoffmann. (For example, pneumatic valves and other moving parts are prone to stick or wear, and clogging.) “Incorrect storage and operator use of such devices also degrade their diagnostic value in terms of statistical process control,” Hoffmann adds.
First and foremost, diagnostics should be installed on critical machinery. “This includes equipment that has an effect on personnel safety, the environment (and other regulatory requirements), production, and equipment that has a high repair-versus-replacement cost,” says Penrose.
The cost of regular diagnostic testing can outweigh the benefits it provides. “This can be the case with small, noncritical systems components,” says Brooks. Too, if a part has a predicted life of 10 years replacement and repair-free operation, it doesn't make sense to test it every day, or install online systems. “In this case, a handheld diagnostic test would be the best choice — used at an interval decided upon by maintenance personnel and engineers. Also, machines with redundant backup systems don't need overly vigilant monitoring,” says Brooks.
There are other examples of where the cost of monitoring a system might be more than the cost of repairing or replacing it. “One might be monitoring the wheel bearing in my bicycle,” says Brillhart. “The cost of replacement is not great, and it is unlikely that a catastrophic failure would occur. Further, the sensor system might be no better than my own observations that the bearing is going bad — for example, from vibration, roughness, and noise.” Also, there is not a large safety concern if the bearing in a bicycle fails. “But this is certainly not true for the bearing in a jet engine, where safety is paramount,” he adds.
“Different levels of diagnostics are required for different types of systems,” agrees Kosnik. This is where scalable diagnostics can come in handy. The ability to take hardware and software and size it to the machine application gives the provider an edge; a diagnostic system that can still collect and store data at fast rates (but be scalable to different classes of machines) helps users justify diagnostics. “Rather than compare the costs of diagnostics to the cost of the overall system, designers should compare diagnostic costs to those of machine efficiency. Not having diagnostics could cost you a lot more than having them,” explains Kosnik.
Engineers know end users want technology like Web-enabled remote monitoring in new and operating systems, but there are additional costs associated with this technology besides initial installation. What's the solution? “Another trend is an increase in the purchase of less-sophisticated diagnostic machinery for use by frontline maintenance personnel. The lower cost of these devices makes this an easy action to justify, especially when compared to the huge cost savings that can be realized by their successful implementation,” says Brooks. In the past manufacturers monitored the health of their machines on a periodic basis. “With the introduction of programmable automation controllers (and their high-speed I/O and online analysis) an increasing number of machines are being designed with permanently installed diagnostic systems. Programmable automation controllers can be used to predict faults before they ever happen, and can generate periodic machine health reports,” says Nipun Mathur, product manager at National Instruments, Austin. One trend is more electronic, smart sensors employed to capture data, perform diagnostic computations (statistical, temporal, spectral) and make appropriate decisions based on the results. Brillhart believes that sensor miniaturization and computing capabilities have accelerated this process.
“We've seen online recalibrations that have eliminated up to 60 minutes of assembly downtime in each eight-hour shift,” confirms Hoffmann.
Machine diagnostics have been around for many years, but technology advancements in the last couple of years (the IC, the PC, Ethernet, databases, storage media, and the Internet) brought diagnostics to the mainstream.
“Today, machine builders are even investing in diagnostic systems to increase the speed and uptime of their machines by collecting machine health data to detect and even auto-correct machine faults,” agrees Mathur.
Fixing problems after they occur means they've already affected the process; in the long run, it is much cheaper to take care of problems before they happen. “Distributed architecture will take over for centralized architecture. This will happen on many fronts including sensors and sensor networks, wireless networks, high-speed serial networks, data collection, and data presentation,” predicts Kosnik. But all systems will eventually fail. How do diagnostics factor in when the inevitable does occur? “When breakdowns do occur, modular systems simplify both diagnostic processes and replacement,” says West.
Of course, internet access (mobile and fixed point) allows for mainstreaming of remote diagnostic services in the face of shrinking staffs.