Wear debris analysis is essential to effectively gauging machinery life. When machine components begin to wear, the evidence can usually be found in the lubricant flowing through the machine. For example, as parts undergo sliding, fatigue or creep, pieces of metal will begin to break off the components and show up as wear debris in the lubricant.
Because so much can be learned about a machine’s health through wear debris analysis, many companies are spending a lot of time and money developing instruments that can provide real-time information about suspended debris in a machine’s lubricant. These instruments allow maintenance personnel to effectively measure the oil’s true condition and predict component failure.
Traditionally, wear debris analysis has been performed at routine maintenance checks, when oil samples are taken and sent to a lab for analysis. While laboratories are equipped to run complete diagnostic checks on the lubricant, in some cases it can take up to several days or even weeks to obtain the oil analysis results.
In the meantime, a distressed component may have already failed, resulting in lost productivity and major repair expense. As new real-time wear debris analysis tools become available, maintenance personnel will be able to detect changes in a machine’s condition immediately and repair a damaged component before catastrophic failure.
Types of Debris Monitoring
The goal of debris monitoring is to determine the presence, size and possible origin of both metallic and nonmetallic wear debris. There are three main wear debris monitoring techniques. The most widely used is off-line monitoring, which requires a physical sample to be taken.
The sample is then analyzed either in an onsite or off-site lab, or by a portable wear debris monitor. In addition to this traditional off-line monitoring method in which analysis occurs away from the equipment, there are two other wear debris analysis techniques: on-line and in-line (Figure 1).
Click Here to See Figure 1 - Oil Analysis Monitoring Positions
On-line and in-line monitors automatically monitor the suspension for wear debris. One advantage of both on-line and in-line monitoring is that outside influences have little impact on these two techniques.
On-line monitors continuously sample and analyze a portion of the flow. However, on-line monitoring can be misrepresentative of the system if the portion sampled is too small relative to the system flow. Results from small samples may not indicate problems, even when the oil actually contains wear debris. This can also be a problem with off-line monitoring.
In-line monitors measure the full flow continuously. In-line monitoring results are immediate and not generally affected by outside influences. These monitors provide continuous real-time data, which allows companies to implement condition trending and condition-based maintenance. In addition, in-line monitoring reduces the cost of oil sampling and laboratory analysis.
Technologies Currently Available
Several companies, using various technologies, offer in-line and on-line products designed to detect wear debris in the fluid. It should be noted that because sensors use different technologies to determine lubricant condition, their ability to detect specific lubricant faults varies (see “Wear Debris Detection Technologies,” sidebar at the bottom of this article).
Eaton Engineered Sensors
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 Smart Zapper® Electric Chip Detector
The Smart Zapper electric chip detector collects ferromagnetic debris and provides an external signal. It has two electrodes spaced apart with a central magnetic surface to attract ferrous wear debris. The electrodes are connected to an external circuit. Once a certain amount of debris is collected on the surface, the circuit is closed and a signal is activated.
The Smart Zapper is able to reduce unnecessary false signals by generating a current pulse that is strong enough to melt away smaller particles while not affecting the larger wear debris particles. Debris is then maintained for further analysis.
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 QDM® (Quantitative Debris Monitor)
The QDM is a magnetic flux sensor that captures ferrous wear debris, provides a signal that is related to the mass of the captured particle(s) and retains the particles for inspection and analysis. Often, although not always, the sensor is installed in a full-flow housing for optimum capture efficiency. For example, Eaton supplies a full-flow, in-line vortex separator (Lubriclone®) that separates debris particles from the oil with efficiencies approaching 100 percent, depending on particle size and permissible pressure drop. For aerated lubrication systems, such as those in gas turbine engines, the separator can also deaerate the oil (three-phase vortex separator). The separator can be furnished with a self-closing valve so that little fluid is lost when the sensor is removed for inspection. If the signal conditioner reaches a predetermined unacceptable wear debris level, it alarms. The signal conditioner can interface with six different sensors at a time.
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MACOM Technologies Ltd.
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 TechAlert™ 30
The TechAlert™ 30 sensor is a magnetic probe sensor unit that is placed directly into the lubricating fluid. It is able to capture ferromagnetic debris. As the wear particles are collected, the onboard microprocessor provides a signal, which indicates the amount of debris captured. A trend of debris captured against time is generated and alarm levels can be set depending upon the application. The TechAlert 30 is intended to be fitted in self-contained gear boxes or in any oil sump.
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 TechAlert™ 20
The TechAlert™ 20 is an on-line sensor designed to measure the amount of ferromagnetic wear debris in circulating lubrication systems. The sensor generates an output that is proportional to the amount of debris captured. When this output reaches a preset threshold level determined in the set-up of the onboard processor, the unit initiates a flush cycle which allows the captured debris to be swept off with the flow of the oil over the sensor head. Determining the time between flushes and the rate of debris generation provides real-time monitoring of the machine based upon the changes in the bulk load of the ferrous debris in the lubricant. The TechAlert 20 is suitable for use in any circulating lubricating oil system. It is especially useful for monitoring fluids from gear boxes, hydraulic systems, rolling element bearings, engine crankcases and process pumps. |
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 TechAlert™ 10
The TechAlert™ 10 is an on-line, flow-through magnetic inductive sensor, which detects both ferrous and nonferrous particles in circulating oil lubrication systems. The sensor output provides information on debris particle size distribution by registering counts in bin sizes. The unit uses a patented screening technique to remove any false alarms caused by the presence of water or air in the fluid. It can be used to monitor a wide variety of machinery, including rolling element bearings, gear boxes, pumps, turbines and engines.
According to Macom Technologies, if used in series, the TechAlert 10 and the TechAlert 20 will provide a revealing picture of wear debris generated at different failure stages from benign wear through advanced failure in machine components.
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GasTOPS Ltd.
 MetalSCAN
MetalSCAN is wear debris sensor that can be mounted in-line without affecting flow resistance or line pressure. The MetalSCAN sensor monitors the disturbance to an alternating magnetic field, which is caused by the passage of a metallic particle through the sensing coil assembly. As a particle crosses the sensor, it couples with the magnetic field. The signal phase for nonferromagnetic metals is opposite to that of ferromagnetic metals. This differentiates between the types of wear metal particles. The sensor transmits the information to a digital signal processor unit, which can monitor up to six individual sensors. It provides multilevel warnings and alarm indications. The sensor does not collect the debris, so there is no cleaning required and no false alarms caused by debris buildup. It is designed for harsh environments. The MetalSCAN is commonly used in both military and commercial applications including pipelines, co-generation plants, and commercial and naval vessels.
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Manor Technology Monitoring Ltd.
 PATROL®
PATROL® is an in-line wear debris monitor that contains a pair of inductive coils in a bridge arrangement around a fluid-carrying tube. As metallic particles pass through the field of coils, they affect the field in two ways. First, because any conductive particle creates an induced current, a power loss from the coil is sensed. Second, ferromagnetic debris increases the flux density around the coil. Circuitry detects the two effects and produces two voltage outputs corresponding to ferrous and nonferrous particle passage. PATROL can monitor ferrous particles as small as 25 microns and nonferrous particles down to 90 microns. Fluid flows through the sensor without significant obstruction, therefore there is no pressure restriction caused by particles. PATROL operates efficiently at temperatures ranging from less than 0°C to 125°C, and in some cases up to 250°C. Because of its ability to operate in this wide temperature range, the instrument is effective in a variety of applications.
As a continuous full-flow in-line debris detector, PATROL avoids the errors and delays that result from laboratory oil analysis and capture efficiency problems common with the magnetic collection-type debris monitors. A proprietary algorithm enables the sensor to issue alerts at stages of abnormal wear.
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T. F. Hudgins Inc. Spinner II Products
 Grid Switch®
The Grid Switch is an on-line, side-stream ferrous wear debris monitor. The unit is encased in a sturdy, aluminum housing. As oil flows into the Grid Switch, it comes in contact with the perforated circuit board comprised of two, interposed electrical grids. When sufficient quantities of wear particles accumulate on the board, the two grids are bridged, connecting the circuit and triggering an alarm. The alarm can be configured to provide either a visual or audible warning. The alarm may also be set up to automatically shut down the engine. A key advantage of the Grid Switch is that it requires no moving parts. It needs little maintenance, and may be cleaned or inspected without shutting down associated equipment. The Grid Switch can be used in engines and other lubricated equipment such as gearboxes, transmissions and compressors.
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Lubrigard Ltd.
 Lubrigard Onboard Oil Condition Sensor
The Lubrigard sensor is an in-line, full-flow oil condition sensor with temperature detecting capability. It directly measures the dielectric loss factor (sometimes referred to as Tandelta), which is known to increase with strongly polar contaminants such as water, glycol and oxidation products. Being electrically conductive, metallic wear debris and soot also increase Tandelta. The dielectric loss factor has a greater dynamic range (typically 0.005 to 0.1 or higher) than dielectric constant (typically 2.2 to 2.9) and is a more sensitive indicator of oil condition. The simplicity of the design leads to a small, compact sensor, which can be fitted to an oil feed line, filter housing or sump. The sensor output is an analog voltage which can be set to various alarm thresholds or can be stored as a time history for subsequent download.
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Spectro Analytical Instruments Inc.
 On-line Model 600T-LP Energy Dispersive X-ray Fluorescence (EDXRF) Process Analyzers
Spectro has developed EDXRF technology for on-line elemental measurements of suspended particles for use in quality monitoring or process control. EDXRF technology allows the user to measure concentrations of elements with atomic numbers from 12 (magnesium) to 92 (uranium). The sensing unit can be configured to sense any of these elements or their compounds; up to six different elements at a time. The advantages of XRF technology are that it is nondestructive, noninvasive and typically needs minimal service. Analysis times can vary from 125 milliseconds to 600 seconds with typical times of 100 to 240 seconds. The Controller cabinet holds the electronics. The Analyzer cabinet contains the flow cell and XRF measurement head.
The measurement takes place in the flow cell, which is made of materials specifically chosen to be inert to the fluid being analyzed. The flow cell has a window that is application-specific based on process variables and energy characteristics. As the fluid goes through the flow cell, the analyzer’s X-ray tube or radioisotope source emits X-rays through the flow cell window into the process fluid. The targeted elements are excited by the X-rays and fluoresce photons back through the flow cell window to the detector, which converts them into an analog output. The analog output is then converted into a scaled signal by the controller electronics. The Model 600(T)-LP is capable of monitoring up to seven sample streams in a single analyzer cabinet. Spectro’s EDXRF analyzer can be used in a wide variety of applications in monitoring the elemental constituents of lubricating fluids.
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New Technologies Lockheed Martin Corp. and FRAS Technology
 LaserNet Fines
LaserNet Fines technology is unique because it combines particle counting and shape classification into a single instrument. The LaserNet Fines Wear Debris Analysis instrument analyzes particles in a fluid using laser-based image processing technology to directly size and characterize particles in the 4 µm to greater than 100 µm range. As a particle counter, the unit measures particle concentration levels in accordance with standard cleanliness ratings: ISO 4406, NAS 1638 and NAVAIR 01-1A-17. As a wear particle classifier, the unit can classify particles greater than 20 µm into wear debris and contamination categories: severe sliding wear, cutting wear, fatigue wear, fibers, nonmetallic particles, free water, air and others.
LaserNet Fines is a commercial PC-based instrument which combines custom laser imaging of particles and artificial intelligence to monitor wear condition of critical machinery components. It analyzes machinery fluids such as hydraulic oil, lubricants and fuels with a laser-imaging optical flow cell. The laser-based camera images the fluid moving through the flow cell to detect wear particles, which are classified by size and type to create reports to identify machinery components for preventive maintenance. It also maintains a database of detected particle images greater than 20 µm to allow trending of historical wear data.
When integrated with FRAS Technology’s DynaSamp on-line fluid sampler, the existing batch commercial unit can continuously withdraw samples from the fluid to create an accurate and automatic on-line particle analyzer; thus removing the chance of contamination when retrieving samples. Lockheed Martin is currently developing LaserNet Fines products for portable and wireless applications.
For more information on the LaserNet Fines see “LaserNet Fines - A New Tool for the Oil Analysis Toolbox” in Practicing Oil Analysis magazine’s September - October 2002 issue.
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Smiths Aerospace Electronic Sensors
 Oil-Line Sensor
Smiths Aerospace is developing an electrostatic oil-line sensor (OLS) to detect both smaller metallic wear particles, or fines, and nonmetallic particles in lubricating oils and liquids produced during the earliest stages of component degradation. The OLS is based on the proven principle of electrostatic monitoring originally developed to detect debris in the gas paths of jet engines using strategically located sensors to monitor the electrostatic charge and specific changes associated with debris generated by wear. Sensor data is usually downloaded to a PC-based analysis package for further processing and trending. The early detection of wear afforded by this direct technique offers a range of benefits in several applications including aerospace, industrial, marine and others.
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Future Technologies Qcept Technologies
CPD-DAQ Sensor and Software
Qcept Technologies is the developer of the patented Scanning Contact Potential Difference (CPD) Sensor. The company, in collaboration with Georgia Institute of Technology, is currently lab testing its CPD-DAQ sensor and software and is confident the technology will provide revolutionary breakthroughs in machine condition monitoring. The CPD sensor is a fast, non-contact, robust sensor. It can measure multiple parameters at high speed with a single sensor, including position, rotational velocity and acceleration, torque, bearing skew, improper alignment, corrosion and contamination, and lubrication condition and breakdown. While the technology doesn’t directly measure wear debris in oil, it can detect the scars in the machine surface left by the wear process. Testing has shown that the sensor and software have the capability to detect wear scars of only 0.3 µm depth, and sensitivity analysis suggests that even smaller deformations can be detected. The sensor has also detected chemical films as thin as 3 nm or less. Additionally, the sensor has been shown to produce a repeatable reliable signal in an oil stream for varying concentrations of oil additives (simulating oil breakdown), and is sensitive to changes in chemistry, contamination and wear. Along with its proprietary software for data acquisition and imaging, and complete inspection systems, the CPD sensor can be used to inspect and monitor a wide range of high-value components in multiple industries.
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Conclusion
Real-time wear debris monitoring technology is far from a mature technology. As technologies advance, sensors are becoming and will continue to become more accurate. They will offer more options and will become more compact. Technologies like those used in the LaserNet Fines are able to discriminate between wear particles and determine the likely origin of a problem before equipment failure occurs.
Click Here to See Table 1 - Summary of Products
The costs of the available on-line and in-line monitors vary widely, based on the technology and features. While it may appear that some of these wear debris monitors are not cost-effective and sending samples quarterly or monthly to a lab is the best maintenance strategy, it is important to consider the options. What would happen if a process-critical machine were to fail today? How much profit is lost for each day of unplanned shutdown? If the answer to that question is “not significant,” then continuous sampling may not be the way to go. However, if mechanical failures can shut down operations for extended periods and/or cost millions of dollars in damages or lost revenue, continuous monitoring could be needed. When weighed against the consequences of failure, the cost of an on-line or in-line monitor might be insignificant.
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Sidebar 1 - Wear Debris Detection Technologies
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Various methods exist for detecting wear particles in lubricants. Below are some common technologies used in wear debris analysis:
Dielectric Constant
A dielectric is an insulator.Dielectric constant is the rate of electric flux density produced in a material to the value in free space provided by the same electric field strength. This technique is able to detect when a change has occurred in the oil. Oil characteristics that affect the dielectric constant are oxidation, water, acids, mixed fluids and wear debris.
Magnetic Flux
With this technique, the concentration of ferromagnetic particles is estimated by means of a fixed magnetic field. The field collects the particles and the field is likewise modified by the presence of the particles. This change in the magnetic flux is monitored by a sensor. The change in flux is converted to ferromagnetic particle concentration by means of an algorithm.
Magnetic Collection Switch/Grid
With this technology, ferromagnetic particles are attracted to an electric grid or plates which serve as opposing electrodes. Current flow between the electrodes signals the presence and general concentration of conductive magnetic particles. Depending on the design, the spacing of the grid/plates and a time-sequence can be used to estimate particle size and concentration of wear debris in the oil.
Induction Sensors
Induction involves modifying the magnetic flux as particles enter the magnetic field. Typically, some kind of inductive coil is placed around a tube or container to create a magnetic field through which the fluid passes. By using electronic circuitry, it is possible to neglect signals from air bubbles. Induction sensors can also differentiate between ferrous and nonferrous debris.
X-ray Fluorescence (XRF) Spectroscopy
XRF identifies and quantifies chemical elements in a sample. The sample is irradiated with X-rays, which causes electrons to move to higher levels. When electrons return to their original state, they emit X-rays at an energy level associated with the particular element. The intensity is proportional to the concentration of the element.
Dielectric Loss Factor
(see description of Lubrigard Onboard Oil Condition Sensor above.)
Laser Imaging
(See description of Lockheed Martin LaserNet Fines above.)
Electrostatic Collection
(See description of Smith Aerospace Oil Line Sensor above.)
Sidebar 1 information cited from:
Hunt, Trevor M., Handbook of Wear Debris Analysis And Particle Detection in Liquids. London: Elsevier Applied Science, 1993.
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Sidebar 2 - Supplier Contact Details
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Eaton Engineered Sensors
1111 Superior Avenue
Cleveland, OH 44114-2584
Phone: 216-523-5000
www.eaton.com
MACOM Technologies Ltd.
17 Glasgow Road
Paisley PAI 3QS
Scotland, UK
Phone: +44 (0)141 849 6287
www.macomtech.net
GasTOPS Ltd.
1011 Polytek Street
Ottawa, Ontario Canada
K1J 9J3
Phone: 613-744-3530
www.gastops.com
Manor Technology Monitoring Ltd.
7 Oldenburg,
Whiteley, Fareham, Hants, UK, PO15 7EJ
Phone: +44 (0)1489 880552
www.manortec.co.uk
T. F. Hudgins Inc.
Spinner II Products
PO Box 920946
Houston, TX 77292
Phone: 713-682-3651
www.spinnerii.com
Spectro Analytical Instruments Inc.
1515 North Highway 281
Marble Falls, TX 78654
Phone: 830-798-8786 option 4
www.spectro-usa.com
Lubrigard Ltd.
PO Box 4186
Stowell, Sherborne, Dorset UK, DT9 4YE
Phone: +44 (0)7989 266 743
www.lubrigard.co.uk
Lockheed Martin Corp.
Naval Electronics & Surveillance Systems - Akron
1210 Massillon Road
Akron, OH 44315-0001
Phone: 330-796-2800
www.lockheedmartin.com
Smiths Aerospace Electronic
Sensors-Southampton
School Lane, Chandlers Ford, Eastleigh,
Hampshire, England,
SO53 4YG
Phone: +44 (0)23 8024 2000
www.shl.co.uk
Qcept Technologies Inc.
250 14th St. NW, Suite 4016
Atlanta, GA 30318
Phone: 404-685-9434
www.qceptech.com
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