Machine condition monitoring as a cost-effective insurance policy
Designers of machinery have traditionally considered condition monitoring to be something undertaken by the user and have therefore not incorporated it from the outset. For a variety of reasons, this situation is changing, so designers need to have an appreciation of what condition monitoring is and the benefits it offers, as well as how it can be implemented.
Monitoring the condition of critical power transmission elements enables component degradation to be identified before it causes a failure. Components such as bearings and gears can be monitored using vibration sensors to detect when wear or damage is starting to occur (Fig.1). Brakes and clutches, on the other hand, may be better monitored using thermal imaging.
By detecting deterioration early, unplanned stoppages can be avoided and further damage can be avoided. For example, a seized bearing could cause the shaft it is supporting to stop suddenly; inertia stored in other components could then cause damage to the shaft, bearing mounting or other components, leading to the repairs being far more complex and costly than simply replacing the failed bearing. Condition monitoring can therefore be thought of as a cost-effective insurance policy.
Condition monitoring can also have direct benefits for the machine builder, especially if an extended warranty or service agreement is supplied with the machine. In addition, the conditioning monitoring system can be used to get a ‘signature’ for the machine before it is shipped, which enables any damage during transportation, trials or commissioning to be identified. Pre-delivery checks can also highlight any components that were either faulty as supplied or damaged during installation.
Although some end user customers are starting to specify that condition monitoring must be installed on new machinery, most still view it as a luxury rather than a sound investment. And very few machine builders incorporate condition monitoring as standard.
Vibration monitoring is the principle form of machine condition monitoring for power transmission systems and today there is a vast range of vibration sensors form which to choose. Hansford Sensors is a relatively young company that has recently introduced a new range of vibration sensors for use on rotating machinery. The HS-130 series sensors are compact devices, having a small body diameter and a weight of just 30g (Fig.2). These features make the sensors useful where space is limited or heavier sensors could affect the machinery.
With a robust stainless steel construction, protection to IP65 standard and non-over-braided, fire-retardant, twin-core screened cable, the sensors are capable of withstanding harsh industrial environments. To complement these 100mV/g accelerometers, Hansford offers the HS-BE series of sensor connection boxes that are easy to use, protected to IP55 and capable of monitoring up to four sensors via BNC connectors.
In some applications users may prefer 4–20mA sensor outputs, so Hansford has also introduced the HS420 series of accelerometers to meet this need. As with the HS-130 sensors, the HS420 models have a robust stainless steel construction, and the 4–20mA signals can be input directly into analogue modules on programmable logic controllers. To mount the sensor, different threads are available plus there is a choice of Quick-Fit or adhesive mount studs.
Hansford offers a choice of models with side- or top-entry connector and braided cables; there is also a submersible version that is sealed to IP68 and capable of being totally submerged up to a depth of 100m. In the near future Hansford will launch an Atex and IEC Ex certified, intrinsically safe version of the HS420 for use in potentially explosive areas.
Data collection
Installing sensors is, of course, only the first step in condition monitoring, as the data must be collected in a way that is convenient and appropriate for the application. One option for data collection is handheld units that gather data from the various sensors located around a machine or plant. SKF, for example, offers a Wireless Machine Condition Detector (WMCD) for use with its Marlin handheld data manager (Fig.3). Data is collected from smart studs and temperature magnets that measure and record vibration, enveloped acceleration and temperature.
Being compact and wireless, the detector is easily portable and therefore extremely versatile. Furthermore, the WMCD avoids the problems associated with conventional wired technology.
By enabling operators to observe, record and monitor machine conditions simply and accurately, corrective action can be taken in a timely manner to optimise productivity levels and minimise downtime. An ‘alert’ condition provides users with an early warning of impending problems, while a ‘danger’ alarm is activated if the system identifies issues requiring urgent attention to prevent potentially serious consequences.
SKF’s WMCD uses Bluetooth technology to collect and communicate data quickly and accurately, which can then be uploaded to the SKF @ptitude Monitoring Suite for viewing and analysing.
While handheld data collectors are adequate for many applications, others require remote data collection and machine monitoring. For these, Monitran offers its Vi-sage combined hardware and web-based monitoring system. Vi-sage can also notify personnel via text messaging and email if user-defined vibration levels are reached.
Employing T-mac Technologies’ range of
GPRS-enabled remote monitoring and control systems, the Vi-sage hardware is available with either eight or 26 input channels and either four or 16 outputs. Users can log into their accounts from any computer with internet access and check near-real-time data, view historical data and control Vi-sage’s outputs. Neill Ovenden, Monitran’s sales and marketing director, comments: "By enabling users to access vibration levels via the web we are making visible, from anywhere in the world, the very information that will help companies realise truly cost-effective remote monitoring and control. There is no need for expensive cables, no need for bespoke software and, if all is well, a reduced need for site visits."
Vi-sage hardware can either be connected directly to accelerometers and other sensors or they can interface with one or more networks of sensors via Monitran’s Multiselect products. Data is uploaded to a website with secure user accounts. Vi-sage hardware settings are made on the web site and then automatically downloaded to the units, where the new configuration takes effect immediately. In addition, the site’s user interface can be customised to present the most relevant data in the most relevant format, and it is easy to set up additional user accounts with appropriate access rights.
Ovenden adds: "It is easy to imagine a scenario where a maintenance engineer may be at home but on call. Upon receipt of an email or text message, the engineer could access the asset’s condition monitoring system and decide whether corrective measures can be implemented remotely or if a site visit is necessary."
Analysis and reporting
National Instruments (NI) is well known for its virtual instrumentation, but the company is also involved in condition monitoring systems. NI says its systems offer simple connectivity to vibration sensors such as radial and axial proximity probes, IEPE (integrated electronics piezo-electric) accelerometers, and speed sensors including laser tachometers and Keyphasors, as well as sensors for process variables such as temperature or dynamic pressure.
NI condition monitoring platforms range from portable USB plug-and-play systems to embedded Ethernet data loggers with onboard analysis and control, all with high-speed 24-bit measurements. If detailed signal processing is required, the National Instruments Sound and Vibration Measurement Suite with the NI Labview graphical development environment provides hundreds of signal processing functions including spectrum analysis and order tracking, plus automated report generation on customisable user interfaces.
One of the latest developments from National Instruments is the NI cRIO-9072 and cRIO-9074 Compactrio systems that enable condition monitoring to be installed cost-effectively on high-volume machines (Fig.4). These Compactrio systems have an integrated hardware architecture that combines an embedded real-time processor and a reconfigurable FPGA within a single chassis, which therefore lowers the cost of Compactrio for volume applications. Engineers can quickly design, prototype and deploy the customisable, commercial off-the-shelf hardware systems for embedded machine control and data acquisition systems using Labview, thereby eliminating the need to spend time and money designing custom embedded hardware.
To reduce the cost of Compactrio for high-volume applications, NI engineers designed the new cRIO-907x systems as integrated systems, with the embedded
real-time processor and FPGA chip on the same circuit board rather than multiple boards as in traditional Compactrio systems. The cRIO-9072 integrated system combines an industrial 266MHz real-time processor and an eight-slot chassis with an embedded, reconfigurable 1M gate FPGA chip, while the NIcRIO-9074 integrated system contains a 400MHz real-time processor and an eight-slot chassis with an embedded, reconfigurable 3M gate FPGA chip.
National Instruments has also worked with FAG, part of the Schaeffler Group, to develop the hardware for the FAG Procheck condition monitoring system. FAG Procheck is described as intelligent, easy to set up, robust and reliable. In addition, the system’s modular construction means it can readily cater for various condition monitoring and maintenance strategies employed across different industry sectors. For example, the system is Atex-certified and can therefore be used in hazardous or potentially explosive environments, and it has a range of communications interfaces so that it can be integrated with a company’s existing plant management or production control and maintenance systems. As well as vibration, further parameters such as temperature, pressure, load, speed, torque, oil status and oil quality can be recorded and correlated with the vibration data. Procheck systems can be expanded and customised by means of expansion slots and digital filter algorithms.
Once set up, the system operates automatically, without further intervention from the user, to measure, record, analyse and issue alerts on vibration data from rotating plant. Data is subjected to an initial assessment by the Procheck system and, if defined alarm limits are exceeded, alert warnings are generated and sent to defined interfaces – where they undergo further assessment. The system can be configured and adapted either by the machine builder, end user customer or by Schaeffler’s maintenance and asset management service division, FAG Industrial Services (FIS). Communication with Procheck systems can be via network (TCP/IP), serial or modem links.
So far we have discussed mainly vibration monitoring, but temperature can also be an important indicator of condition. Optris offers a broad range of infrared thermometers, the latest of which is the Optris CT laser high-performance series for applications from
-40 to 975¢ªC. One of the main advantages of this sensor is the small spot size that enables accurate non-contact temperature measurements to be made.
It allows low- and high-temperature measurements to be made with a spot size as small as 0.9mm at a range of 70mm without the need for mechanical choppers; maximum measurement range is 1260mm. The CT laser operates in ambient temperatures of up to 85¢ªC without cooling, giving a selectable analogue output of 0/4–20mA, 0–5/10V or thermocouple type K or J. Alternatively, the CT series infrared thermometers are available with an integrated digital Profibus DP, USB, RS232, RS485 or Can interface.
