Watching for the red alert01 April 2006

Plant engineers face a dilemma. Is it best to wait for something to break down or undertake maintenance work at pre-planned intervals (which may mean performing maintenance and causing downtime when it is not really needed)? Or should they establish a system to diagnose problems when they first show signs of arising? While the latter has to be the preferred option, it is certainly the hardest to apply.

Unusual noise and vibration are usually fairly good indicators of something going wrong, but heat is an even better signal, because it shows up problems at an earlier stage, as well as those that are quiet, but potentially just as troublesome.

Bearings may appear to be running perfectly smoothly, for example, but generate more heat than they can dissipate, if they become misaligned by just a few micrometres. If left unchecked, this can lead to lubricant failure, changes in dimensions and total failure in a matter of hours. Electrical systems normally run silently, so only temperature can be used as a means of diagnosing problems. Oxidised, loose or dirty electrical connections all generate excess heat, as do fuses carrying currents close to their overload value.

These can all be monitored using temperature sensors, but a more immediate result can often be obtained at much lower cost by using an infrared camera. These devices, originally developed for military night vision systems, have become smaller, lighter, more accurate, easier to use and much less expensive that they were only a few years ago.

The British-made IRI 4010, from Irisys of Towcester, has a 160 x 120 pixel chip sensor. It is designed to be carried around in the hand, using a pistol grip, and costs approximately £3,400. The infrared image is displayed on a 3.5-inch LCD screen on the back, as either a monochrome, ironbow or rainbow-coloured display. A laser spot, when activated, can be used to mark the target. It self adjusts the image in real time and can identify, measure and record temperatures from -10 ºC to +250 ºC. The device weighs only 750g. Up to 1,000 images can be stored and retrieved at full resolution, using a supplied SD memory card. Two measurement cursors highlight temperatures and temperature differences. Battery life from the replaceable lithium ion battery is four hours. The device builds on the company's £1,000 IRI 1011 model, which has a 16 x 16 pixel chip, but can produce a higher resolution display on an attached PDA by utilising some clever interpolation software.

Director Dr Steve Hollock says the target user is "the man in green overalls" and typical applications include electrical, mechanical and process and offshore industries. The latter often use it for detecting levels in tanks and while they would prefer something explosion proof and intrinsically safe, they are apparently willing to use whatever is available, using an "exemption for occasional use", he states.

In terms of predictive maintenance, infrared systems are often used for monitoring high-voltage equipment where it's not advisable for workers to stand close to equipment to take measurements. Modern sulphur hexafluoride gas-filled circuit breakers, such as those made by ABB, greatly improve reliability. They still have to be monitored, however, and include pressure sensors to detect possible leaks.

ABB has been doing a lot of work on using wireless technology to interface to sensors. Low- power radio data gathering and monitoring is well established in SCADA systems for the water and sewerage industries, but engineers are increasingly interested in the possibilities offered by emerging standards, such as Bluetooth and Zigbee, for monitoring industrial automation equipment. ABB has come up with its own system called Wireless Interface to Sensors and Actuators (WISA), which incorporates military-style frequency hopping, and is said to be capable of ensuring reliable real-time machine control, as well as gathering diagnostic information.

Online condition monitoring to anticipate automation system degradation, using hard-wired cables, has become quite widespread. One of the pioneers of automation system monitoring is Quin Systems, based in Wokingham. Quite a number of companies claim to offer remote diagnostics, anywhere in the world, but Quin is one of the few companies that has demonstrated this, using the Internet.

Rockwell Automation has just brought out a small, low-cost DeviceNet module that clips to the side of a standard overload relay and can transmit information about unusually high or low electric motor currents. While high currents indicate that something is getting stuck, low currents may be indicative of drive shaft failure, pumps that are no longer pumping fluid or lost conveyor belts. The device is 18mm wide and has an entry-level price of only £20, to which should be added a further typical £40 for a compatible circuit breaker and overload relay. Designated the 193-EDN Starter or DeviceNet Starter Module, it is designed to report to a PLC, personal computer or human machine interface which can, in turn, be connected to a wider automation line or plant control system.

As well as monitoring temperature, machine performance or electric motor currents, much can be gained from monitoring the condition of oils and lubricants, and ensuring they are kept clean.

According to Castrol, a US study has shown that less than 10% of bearings reach their expected fatigue life due to contamination, and bearing manufacturers say 85% of all failures are due to poor oil cleanliness. Research at Oklahoma University has shown that a normal system can ingress 10 to 100 million particles per minute that are greater than 10 microns size. Meanwhile, a study by the University of Massachusetts concludes that wear costs the US 6% of GNP - $240 billion. Ford is said to have found that 75% of breakdown costs are lubricant related, while Saab is said to quote a figure of 90%.

Part of the solution is to improve engine air intake and oil filtration. According to General Motors, going from 40 micron to 30 micron filtration reduces engine wear by 50%, while going to 15 micron filtration reduces it by 70%. The US Navy is said to have achieved a four-fold increase in bearing life by improving filtration by 70%.

We have no way of verifying these US figures ourselves, and the University of Massachusetts figure for wear probably includes a whole range of wear problems, not all of which have anything to do with lubrication. However, anecdotal experience from Blaw Knox, Rochester, strongly reinforces the general impression. The company issued detailed guidelines on how the road paving machines it manufactured should be lubricated - what with, where and how often, given different circumstances.

Following the lubrication schedule religiously proved beneficial to one Belgian company, which still operated one of the first paving machines the company had built some 30 years earlier. On the other hand, a work team with a major UK construction company never lubricated its machines, and usually had to buy a new replacement machine every six months.

Castrol says improving the cleanliness of lubricants from ISO 19/16 to 15/12 can be expected to double bearing life, as will reducing moisture content from 1000ppm to 250ppm. A three-year study by the British Hydraulic Research Association has revealed that effective contamination control increased Mean Time Between Failures by 10 to 50 times. This again is confirmed by the Blaw Knox experience, where it was found that hydraulic reliability was enhanced by choosing the finest pored filters that could be obtained, provided they were changed when they started to show significant pressure drop.

This raises the issue of when to change lubricants, oil and filters. The traditional approach was always to do so according to hours run or miles driven, but the true cost of an oil change is 40 times that of the oil and, according to Castrol, for every £3 spent on preventive maintenance according to a schedule, £1 is wasted because it is not yet really necessary. One answer is to have an Oil Condition Monitoring (OCM) programme to monitor trends, particularly oil cleanliness and moisture content. A contamination control programme is then needed, which sets achievable targets for the cleanliness required. Sources of contamination need to be identified and eliminated, and the effectiveness of filtration assessed and improved.

Effective management of these predictive, and other, maintenance tasks that diagnostics may have revealed is the task set by software packages such as Agility from SoftSols. The new module, Agility Mobile Expert, includes work order status tracking, site and asset histories, signature capture, spare part usage, remote stock enquiries, and the ability to work offline when out of wireless network range, resynchronising when the network connection is re-established.

Users include The Trafford Centre in Manchester, which has 230 retail outlets, and 47 catering and leisure facilities spread across three floors. Andy Robinson, building services manager explains: "The previous Computerised Maintenance Management System (CMMS) was becoming an administrative burden and wasn't easy to use. Moving to Agility eliminates the need for paperwork as our engineers can receive work orders directly on their PDA devices through the mobile expert feature. It is also a lot more intuitive for our helpdesk staff, who can operate every aspect of the system."

Irisys www.irisys.co.uk
Quin Systems www.quin.co.uk
Rockwell Automation www.rockwell.co.uk
Castrol www.castroladvantage.com
Agility from SoftSols www.getagility.com

SOE

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