Inspect your rotating machinery bearings with Portamonitor® the best bearing checking instrument. Choose acoustic emission technology in your condition monitoring practices. Acoustic emission testing is better than vibration monitoring. Click on the Portamonitor® below for a faster, better, cheaper method.

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Acoustic Emissions

Acoustic emission non-destructive testing is vital for bearing condition monitoring. Bearings are used in a wide array of rotating machinery such as pumps, engines, motors. Damaged bearings cause inefficiency resulting in undue downtime and costs. If left unchecked, it could eventually catastrophic machinery failure. By addressing correct bearing lubrication early and choosing Portamonitor bearing test equipment you can save time and cost, whilst improving safety.

What is condition monitoring?

Using appropriate condition monitoring tools such as acoustic emission testing matters because bearing wear and tear can result in wasted time, money and resources.

When to use a bearing tester instrument?

The handheld Portamonitor can be used for pre-service bearing condition testing as well as in-service testing and condition monitoring.

How to use a bearing condition tester?

Portamonitor® is incredibly easy to use:
1. Simply turn the unit on
2. Apply ultrasonic gel to the sensor and surface you are testing
3. Press the search button and place on bearing for 10 seconds
4. Results will then show
A demonstration video of how to measure machine health can be found here: Portamonitor® Demonstration Video

Benefits of Portamonitor® Reporting Options compared to other bearing checkers

Portamonitor® has two units of measurement for bearing health: decibel and Distress®. Distress® provides an instant indication of the health of the bearings. It measures impacts, friction and surface deformation caused by micro-pitting and fractures. Algorithms inside the Portamonitor® sort this data for comparison against acceptable limits categorised by a number.

Utilising acoustic emission condition monitoring, the Portamonitor® operates precisely how the user expects and wants – indicating the current state and progressive condition of bearings in two simple and easy to understand values:

a. Distress Level – Current state: ‘OK’ ‘SUSPECT’ ‘POOR’ (inc. numerical equivalent).

b. Decibel Level – Trend (Ability to track degradation over time).
Display on the bearing checking instrument

The display on the Portamonitor® will show a numeric value indicating the level of distress, for instance: 5-10 indicates the system in “OK”. Between the value of 10-15 indicates the system is “SUSPECT”, and requires further monitoring, whereas >15 indicates a “POOR” system and requires attention.

Enquire now to find out more about how Portamonitor® will help you.

A condition monitoring system will assess the early detection of failure and acoustic monitoring systems or acoustic emissions techniques are essential. Acoustic condition-based monitoring will provide warnings of developing problems as well as the potential to apply new techniques. Acoustic monitoring equipment will use techniques based on the use of accelerometers, the vibration analysis can be classified into three categories. Acoustic emission monitoring systems provide a range of features and areas of excellence, they’re known for providing the best protection and longest period of warnings for potential damage and eventual failure. Acoustic monitoring systems can help to prevent the worst and when problems have been identified, the appropriate technologies can be recommended in order to provide a complete picture of the likely failure mechanism.

The acoustic condition monitoring indicators that we manufacture are condition indicator tools that use powerful monitoring techniques in order to analyse the heath state of machinery, especially when it comes to the health and lubrication of bearings. It includes magnetic sensors that can be attached to a machineries outer casting and take readings over a short period of time, helping to assess the condition of the moving parts within. An overall noise decibel level (dB) will be returned with a distress level, measurements can then be analysed quickly and compared to other readings in order to discover if preventative maintenance is necessary. Robust ultrasonics can take 1000 readings between charges, this is done through standard USB leads to ensure easy charging for users. The system will aid identification of mechanically deteriorated bearings and bearings that have inadequate or contaminated lubricant.

Acoustic Condition Based Monitoring

The acoustic ultrasonic monitoring indicators that we provide here at Coltraco aim to enhance preventative maintenance and condition based monitoring through comparing accurate and repeatable results to past measurements. These tools are essential in order to plan for future repairs and make quick fixes before bigger faults occur, they’re also extremely sensitive, so the results are very accurate. The acoustic emission leak detection will detect high frequency ultrasonic stress waves that are associated with friction and other faults with machinery in poor conditions. Acoustic conditioning is most suitable for use on motors, pumps, fans, generators and other rotating machinery applications, the results include two outputs that will be displayed simultaneously, decibel (dB) and a Distress level.

Coltraco’s acoustic based monitoring tool is the first of its type in the world, the pocket size Portamonitor includes a powerful ultrasonic monitoring technique to test bearings and rotating machinery and is suitable for a number of industries including ships and vessels. This tool will detect stress waves that are associated with friction and poor conditioning and will include a range of quick and efficient readings, then the acoustic Portamonitor will return an overall noise decibel and Distress level on a clear display. Our tools come with full instructions and ensure ease of use so that you can make sure that safety and integrity is enhanced and accessible. The acoustic monitoring Portamonitor has the ability to take 1000 readings between charges and is the perfect condition monitoring tool for making sure that bearings are in good condition and that they are adequately lubricated in vessel’s engine rooms, bearings in motors, pumps, fans, gearboxes and other rotating machinery.

Acoustic Monitoring for Machinery

When it comes to machinery, early detection of failures and issues are crucial, listening and measuring with acoustic emission testing procedure can easily distinguish healthy bearings from damaged ones, this is through the onset of noise. The acoustic ultrasonic testing will cover a range of data including vibrations, rotations and temperature measurements, as well as alarms, acoustic monitoring in industry really is an effective solution. The acoustics will produce a broad sound spectrum that is usually monitored by vibration in low frequencies, some specific defects will produce acoustic waves that come with high frequencies, this will impact for bearings and gearboxes, friction or rubbing for lubrication and cavitation for pumps. One of the biggest advantages of acoustic condition monitoring equipment is that it’s easy to monitor bearings and degradation that could be masked in low frequency analysis. The use of ultrasonic resonant sensors acts as a mechanical amplifier of high frequencies, ultrasonic acoustics comes with an excellent signal-to-noise ratio that allows the detection of weak variations from background vibrations. The results show that acoustic ultrasonic technology is selective in highlighting at an early stage, defects against low frequency problems as well as the great effectiveness in low speed equipment monitoring.

The Portamonitor is a state of the art condition monitoring tool, it’s sensitivity means that it provides accurate results when detecting faults, the technology aids detection of deteriorated bearings when it comes to operating machinery, it can also identify bearings that may have inadequate lubrication or lubricant contamination. The Portamonitor provides unique signal detection and processing for bearings in motors, pumps, fans, gearboxes and other rotating machinery equipment and applications. The readings will provide insight into the planning of future repair actions, as well as assist in identifying the need for improved lubrication.

How it Works

The acoustic instruments that we provide will listen for frictions and impacts that are caused by poor lubrication or bearing damage. Next, sound is generated by the bearings and this will propagate through the machine, using a sensor that sends a signal, the user will then be able to detect the noise by using signal processing, the user can then determine the condition of the bearing. A decibel reading will show the intensity of the signal being received, essentially this is how ‘loud’ the high frequency sound product by the bear is, it’s not affected by sound that’s audible to the human ear. The reading will increase with deteriorating function of the bearing, the decibel reading is a very repeatable measurement, if the state of the bearing hasn’t changed, then the decibel reading won’t either. It’s recommended that logs are kept of the decibel reading for each site, this will permit identification of deteriorating bearings as the decibel reading begins to increase. The Distress signal will show how much the decibel reading is varying in level throughout one measurement, this will represent how much the bearing is knocking, clanking or grinding. This is a useful indicator of whether the bearing is damaged, poorly lubricated or malfunctioning, and whether it requires maintenance. This is useful as it’s automatically calculated and displayed by the Portamonitor so it will need minimum input from the yser and will give a reliable and instant indication of the state of the bearing. 

The Science of How it Works

Condition monitoring solutions using acoustic emission works on the principle of using transient elastic waves to detect the rapid release of strain energy caused by deformations or damage within the surface of materials. Strains, stresses and impacts produce transient stress (elastic) waves which can be effectively detected and occur in the very early stages of bearing degradation

Bearing Inspection Procedure

In laypersons terms, the acoustic instruments that we provide will “listen” for frictions and impacts that are caused by poor lubrication or bearing damage. Next, sound is generated by the bearings and this will propagate through the machine, using a sensor that sends a signal, the user will then be able to detect the noise by using signal processing, the user can then determine the condition of the bearing.

A decibel reading will show the intensity of the signal being received, essentially this is how ‘loud’ the high frequency sound product by the bear is, it’s not affected by sound that’s audible to the human ear. The reading will increase with deteriorating function of the bearing, the decibel reading is a very repeatable measurement, if the state of the bearing hasn’t changed, then the decibel reading won’t either. It’s recommended that logs are kept of the decibel reading for each site, this will permit identification of deteriorating bearings as the decibel reading begins to increase.

The Distress signal will show how much the decibel reading is varying in level throughout one measurement, this will represent how much the bearing is knocking, clanking or grinding. This is a useful indicator of whether the bearing is damaged, poorly lubricated or malfunctioning, and whether it requires maintenance. This is useful as it’s automatically calculated and displayed by the Portamonitor so it will need minimum input from the user and will give a reliable and instant indication of the state of the bearing.

More About Acoustic Monitoring

Acoustic emissions are one of the technologies for health monitoring and diagnosis of rotating machines, extensive research and investigation has shown the effectiveness of acoustic technologies in identifying types of defects in machinery. The application of signal processing methods are necessary for monitoring machinery and the use of condition monitoring tools has found to be effective in denoising the necessary signals. The Portamonitor is an innovative tool that allows these types of acoustic assessments to be carried out safely and accurately, it's the first of its type in the world, so when it comes to acoustic ultrasonic technology, Coltraco are the team to call on. 

The Portamonitor is pocket size so can be carried around as needed, it includes only the most pioneering ultrasonic monitoring techniques, allowing you to test bearings and rotating machinery for a number of industries. The tool works by detecting stress waves that are associated with friction and poor conditioning, after providing a number of quick, effective and efficient readings, the tool will return an overall noise decibel and distress level on a clear display. The Coltraco Portamonitor comes with full instructions and guarantees ease of use, ensuring enhanced safety and integrity. What’s more is the tool can take up to 1000 readings in between charges and it is an ideal condition monitoring tools for ensuring that bearings are in a good condition, as well as being adequately lubricated in vessel’s engine rooms, bearings in motors, pumps, fans, gearboxes and other rotating machinery. 

What are the benefits of Portamonitor® bearing indicator?

The Portamonitor is pocket size so can be carried around as needed, it includes only the most pioneering ultrasonic monitoring techniques, allowing you to test bearings and rotating machinery for a number of industries. The tool works by detecting stress waves that are associated with friction and poor conditioning, after providing a number of quick, effective and efficient readings, the tool will return an overall noise decibel and distress level on a clear display. The Coltraco Portamonitor comes with full instructions and guarantees ease of use, ensuring enhanced safety and integrity. What’s more is the tool can take up to 1000 readings in between charges and it is an ideal condition monitoring tools for ensuring that bearings are in a good condition, as well as being adequately lubricated in vessel’s engine rooms, bearings in motors, pumps, fans, gearboxes and other rotating machinery.

More About Coltraco

At Coltraco, all of our products are carefully hand built and undergo rigorous quality testing to make sure that they meet the high standards expected by our customers, as well as provide them with long term reliability.

Our customer care includes:

  • 1 year warranty
  • Guaranteed against defects in materials and workmanship
  • Technical support for the life time of all equipment, by telephone or email

The Portacare Plan

As well as standard after sales customer care, you can upgrade to Coltraco’s Portacare plan, our 3-5 year total care and maintenance package includes:

  • Capping the cost of ownership during the term you choose.
  • Guarantee maximum operational ability so the equipment is ready to use whenever you need it.
  • Backup units are provided in the event of fault.
  • Supporting you above and beyond the warranty.
  • Providing you with peace of mind so that you can have confidence that your Portamonitor is maintained.

Enquire now to find out more about how Portamonitor® will help you.

What are the advantages of condition monitoring?

Using appropriate condition monitoring tools matters because damage to bearings can result in undue downtime, wasted time, money and resources.

When to use a bearing tester instrument?

The handheld Portamonitor® can be used for pre-service bearing condition testing as well as in-service testing and condition monitoring.

Benefits of Portamonitor® condition monitoring report Options

The Portamonitor® has two units of measurement for bearing health: decibel and Distress®. Distress® provides an instant indication of the health of the bearings. It measures impacts, friction and surface deformation caused by micro-pitting and fractures. Algorithms inside the Portamonitor® sort this data for comparison against acceptable limits categorised by a number.

Utilising acoustic emission condition monitoring, the Portamonitor® operates precisely how the user expects and wants – indicating the current state and progressive condition of bearings in two simple and easy to understand values:

a. Distress Level – Current state: ‘OK’ ‘SUSPECT’ ‘POOR’ (inc. numerical equivalent).

b. Decibel Level – Trend (Ability to track degradation over time).
Display on the bearing checking instrument

The display on the Portamonitor® will show a numeric value indicating the level of distress, for instance: 5-10 indicates the system in “OK”. Between the value of 10-15 indicates the system is “SUSPECT”, and requires further monitoring, whereas >15 indicates a “POOR” system and requires attention.

How does bearing monitoring save cost and time?

The Portamonitor® is a low cost and is very easy to use bearing servicing tool and easy to integrate into scheduled maintenance. Using this regularly extends the lifetime of key pumps, bearings and gearboxes saving significant amounts of money over the lifetime of the vessel, extending the time between machinery replacement and ensuring failures do not occur at critical times. The Portamonitor® offers faster processing time at sensor level, thus reducing overall maintenance time.

Why buy a bearing checker?

Almost all machinery that moves requires bearings for its rotating equipment. Degradation of the bearing happens over time. Condition based monitoring is important as bearings will fail for a number of reasons but the key take away is that ALL bearings will degrade at some point and if they are left unchecked, maintained or replaced WILL fail. A key failure comes from a lack of bearing lubricant. Using bearing monitoring equipment to understand the root cause of damage can help prevent future failures. According to ISO 15243, damage to rotating machinery left undiagnosed can actually mask the underlying cause if left too long.

Below is an example showing the progression of bearing damage that has become more severe, thus hiding the root cause:

Failure modes as categorised by ISO 15243

Do bearings need lubrication?

Most decay in bearing quality occur when lubrication has been used up in the bearing. Identifying machinery health and refilling the oil in the bearing a key way of extending life span. The Portamonitor® is the ideal tool for lubricant analysis condition monitoring. The Portamonitor® is a preventative bearing maintenance tool, a proven technology that can help users identify the onset of catastrophic failure and take planned action to prevent failure of machinery.

What types of bearings are commonly measured by the Portamonitor®?

Using acoustic bearing monitoring, condition and lubrication state of all rolling element bearings, examples such as: needle bearing. It is also ball bearing inspection method as well as roller bearing inspection.

The Portamonitor® also tests all hydrostatic and hydrodynamic bearings, examples such as: plain bearing (journal bearing, linear bearing, thrust bearing) & trankpin bearing.

What bearing rotation speeds can be measured by the Portamonitor®?

As low as 45 rpm to as high as 8,000 rpm.

Why use acoustic emission monitoring instead of vibration analysis?

Acoustic emission testing is very effective at detecting deformation due to formation of cracks or friction which occur in the very early stages, independent of machine dynamics. These defects give off an acoustic emission pulse well before they can be detected by vibrational analysis. Unlike Vibrational Analysis, the Portamonitor® is not influenced by the natural frequency of the machinery. Using acoustic emission monitoring, there is no need to remove the bearing for testing.

What types of bearing failure are covered by the Portamonitor®?

Excessive load – bearing damage and housing causing premature fatigue/failure

Overheating – excessive temperatures can anneal the ring and bearing material, reducing hardness causing early failure.

Beating Lubrication levels and contamination – causes friction contacts and mechanical impacts, respectively.

Crack formation – early stages of wear as a result of impacts or excessive loading can cause deformation and will evolve to failure.

Where are bearings found?

Steel production facilities

  • Steel and iron use cold rolling mill machinery. The working rolls of the plant are the most extensively monitored. This is quite a challenging bearing monitoring environment due to high temperatures, high and low-speed operation, as well as high contamination of water and debris

Mining industry

  • Slow turning rolling element bearings require monitoring in this industry. Machinery such as crushers, stackers, conveyors, vibrating feeders, magnetic separators, slurry and vacuum pumps, classifiers, agitators and compressors.

Paper processing industry

  • Paper making machine bearings operate under very high temperatures and can be vulnerable to fractures of the inner ring, causing stoppages in production. Monitoring is done to determine the condition of the rolling-element bearings of the rolls, roll alignment, balance, and the condition of the electric motors and gearboxes.

Cement industry

  • Many machines in this industry require monitoring of bearing condition, including crushers, mills, separators, roller presses, separators, conveyors, feeders, air compressors and fans. Most of which use rolling-element bearings powered by electric motors.

Thermal power industry

  • Gas and steam turbine generators and combined cycle plants require their most critical machines monitored. Dynamic rotating machines use high-speed rotating parts. The cost of failure in this industry is far-reaching.

Maritime industry

  • Diesel engines, gas turbines and nuclear reactor powered ships utilise bearings in all areas, from crankshafts to pistons and pumps. Also, gearboxes fans and other motors onboard, such as alternators used to generate electricity.

When using the Portamonitor® for asset condition monitoring management, is it affected by environmental conditions?

The Portamonitor is not affected by environmental conditions which can mask late-onset bearing damage when analysing vibration data. Elastic waves that are produced by fractures or debris inside bearing systems produce various frequencies – all of which are analysed automatically inside the Portamonitor and converted to an easy to understand value allowing first-time users the ability to conduct advanced maintenance.

Equipment Inspection Procedure

The Portamonitor® bearing condition tester is incredibly easy to use.

1. Simply turn the unit on
2. Apply ultrasonic couplant to the sensor and surface you are testing
3. Press the search button and place on bearing for 10 seconds
4. Results will then show

A demonstration video of how to measure machine health can be found here: https://www.youtube.com/watch?v=1ebGUHcW0gI&t=11s

Enquire now to find out more about how Portamonitor® will help you.

LPG Vessel Field Trial using Portamonitor® and Portasonic® 2.FL0

Coltraco Ultrasonics’ engineers had a busy night successfully testing Portamonitor® and Portasonic® 2.FL0 during field trials onboard a LPG Vessel.

Learn more about how our Safeship® technology is right for you with the acoustic emissions portable bearing indicator Portamonitor® and portable ultrasonic transit time flow meter Portasonic® 2.FL0.

Many cases of catastrophic failure in bearings have occurred throughout the industry that could have been avoided if effective condition monitoring and maintenance had been in place. The following case study of bearing failure has been taken from the Australian Transport Safety Bureau:

On 7 March 1997, the Polish flag general cargo vessel Lodz 2 was using one of its own cranes, discharging a general cargo of steel products, including bundles of steel pipes, from no. 2 hold and tween deck. At about 0740, the sixth load of steel pipes, for that morning, was being discharged onto the wharf by no.1crane, a 12.5-tonne capacity crane situated on the aft end of the forecastle on the ships centreline. The load, weighing approximately 8.6 tonnes, consisted of 18 lengths with diameters varying up to 273 mm. As the load reached the side of the ship, there was a violent jolt and a bang as the slew bearing failed, then the crane fell from its pedestal into the port tween deck of no. 2 hold.

The jib struck the port bulwark, setting it down and out from the ships side, while the body of the crane hit the inboard edge of the port hatch coaming, before rotating through 180∞ and finishing up, upside-down, in the tween deck. The driver had fallen with the cab of the crane, approximately 17 metres into the tween deck from the cranes position on its pedestal. The crane was severely damaged and the badly twisted jib had to be cut up to remove it from the ship.

https://www.atsb.gov.au/publications/investigation_reports/1997/mair/mair110/ 

Enquire now to find out more about how Portamonitor® will help you.

A condition monitoring system will assess the early detection of failure and acoustic monitoring systems or acoustic emissions techniques are essential. Acoustic condition-based monitoring will provide warnings of developing problems as well as the potential to apply new techniques. Acoustic monitoring equipment will use techniques based on the use of accelerometers, the vibration analysis can be classified into three categories. Acoustic emission monitoring systems provide a range of features and areas of excellence, they’re known for providing the best protection and longest period of warnings for potential damage and eventual failure. Acoustic monitoring systems can help to prevent the worst and when problems have been identified, the appropriate technologies can be recommended in order to provide a complete picture of the likely failure mechanism.

According to studies conducted by the Mobius Institute. Defects are encapsulated in the following categories, shown in the following chart:

84% of degradation occurs once installed. Monitoring is essential for the detection of faults caused by fatigue or stress due to excessive load or use. Incorrect lubrication, as well as insufficient levels of lubrication, can cause friction which can lead to fractures among other defects. Also, contamination, both in the bearing housing or the lubrication can damage and reduce the life of bearings.
A bearing measurement tool can detect abnormalities caused by these and allow preparations for maintenance or replacement, ultimately avoiding failure and saving money. The cost of bearings is highly variable and depends on the position of the defect and if any associated damage has occurred as a result of the initial bearing failure. Figures can rise quickly, in severe cases when bearing monitoring has been limited and total failure has occurred then the cost can be tremendous. According to the International Institute of Marine Surveying the cost of some vessel machinery, by example:

 

DAMAGE COST (£)
Main Engine Crankshaft Failure 4,000,000.00
Turbocharger Failure (Large main engine) 580,000.00
Rudder Damage (Bulk carrier, US flag) 705,000.00
Reduction Gearbox Damage (push tug) 350,000.00
Auxiliary Engine Failure 380,000.00
Cargo Crane Slew Ring* 506,000.00

 

Cost has been converted to pounds (nearest thousand): See https://www.iims.org.uk/machinery-underwriters-problem/ for the original.
*case study included in this article: https://www.atsb.gov.au/publications/investigation_reports/1997/mair/mair110/

All of the above contain bearings and if not monitored, or repaired when needed. The results could be catastrophic failure. This is just the cost of the replacement machinery, of course, this varies, especially when only small replacements are needed. A failure of a bearing is not just the part itself, the cost to a vessel owner is repair, fitting and downtime in dock and loss of earning whilst not operational. Needless to say, the process can become extremely expensive.

Of course, this is not limited to the shipping industry, other industries suffer the same problems with machinery failure and can be just as, or even more expensive to deal with. Without systematic procedures and planned maintenance (enabled by condition monitoring) then cost can be very damaging to a business.

The main bearing inspection indicators that we manufacture are condition indicator tools that use powerful monitoring techniques in order to analyse the heath state of machinery, especially when it comes to the health and lubrication of bearings. It includes magnetic sensors that can be attached to a machineries outer casting and take readings over a short period of time, helping to assess the condition of the moving parts within. An overall noise decibel level (dB) will be returned with a distress level, measurements can then be analysed quickly and compared to other readings in order to discover if preventative maintenance is necessary. Robust ultrasonics can take 1000 readings between charges, this is done through standard USB leads to ensure easy charging for users. The system will aid identification of mechanically deteriorated bearings and bearings that have inadequate or contaminated lubricant.

 

Why use acoustic emission monitoring instead of vibration analysis?

Acoustic emission testing is very effective at detecting deformation due to formation of cracks or friction which occur in the very early stages, independent of machine dynamics. These defects give off an acoustic emission pulse well before they can be detected by vibrational analysis. Unlike Vibrational Analysis, the Portamonitor® is not influenced by the natural frequency of the machinery. Using acoustic emission monitoring, there is no need to remove the bearing for testing.

What are acoustic emission testing limitations?

Portamonitor is a handheld inspection product. It does not provide constant monitoring and as such does not have a remote alarm to alert when bearings need attention.

Compare Vibration Analysis Equipment (VA) vs. Acoustic Emissions (AE) Testing?

Both VA and AE are methods for monitoring the condition of bearings and are used to diagnose and determine severity of defects within various machinery.

Vibration Analysis testing: Accelerometers are devices built to conduct vibrational analysis, they are designed to pick up vibrations as an indicator of defects. Excessive vibrations can indicate a serious problem that requires maintenance before a catastrophic failure occurs. Complex software is then used in conjunction to analyse the vibrational data in order to diagnose machinery faults. This is the basis of VA.

Acoustic Emission: AE is used for effectively monitoring different machine conditions; balanced, unbalanced, misaligned and defecting bearings. Monitoring equipment using AE works on the principle of using transient elastic waves to detect the rapid release of strain energy caused by deformations or damage within the surface of materials. Strains, stresses and impacts produce transient stress (elastic) waves which can be effectively detected and occur in the very early stages of bearing degradation.

Why use AE?

AE is based on frequencies much higher than accelerometers using VA and with a larger range than what’s capable with VA, typically around ~ 10 Hz-30 kHz, AE will operate within ~20 kHz-1 mHz, but more usefully around 100 kHz. The immediate advantage of this is that mechanical noise is no longer present in this range which allows the detection of defects in the very early stages. It is very important to be able to distinguish between machine noise and defect noise in order to avoid misdiagnosis.

Defect frequencies vary considerable and are highly dependent on machinery designs and component geometry and are also a function of bearing geometry, pitch, roller diameter and the relative speed between raceways. Fortunately, AE is less geometrically sensitive than VA. In order to establish defects using VA, a “base-line” needs to be established from the initial conditions of the machinery and used to indicate an irregular condition by monitoring an overall trend that will highlight anomalies.

Diagnosis using VA is not an easy task and requires highly technical knowledge, as well as being very time-consuming. An immediate drawback when monitoring the general condition of the entire machine is that the overall trend level may not show any significant change if the machine fault is not severe, or the signal is insensitive to the fault. With AE the detection of acoustic pulses are usually independent of any machine noise interference, especially at the high operating frequencies which is ideal when baseline frequencies are not known. This gives confidence that defects will not be missed.

Moreover, experiments conducted to test bearing operation at low speeds between [10-100 rev min-1] have shown that AE is effective at these speeds [Alshimmeri, 2017] and can effectively detect bearing defects when previously it was assumed that AE was mainly effective at high speeds. It seems that excessive loading will cause disruptions in the obtained signal as it can affect signal attenuation (or, how much signal is lost as a function of distance to the source). It has been found that the attenuation of signal remained constant at higher loads and can be distinguished fairly easily.

Defects

Bearing defects are essentially random but occur in natural stages and will usually worsen due to dynamical strains on the bearing components. Generally speaking, advanced stage defects will produce high intensity but low-frequency signals. The very early stages of wear will occur as a result of minuscule abnormalities, such as very small contaminants in lubrication, or small stresses and deformations in the material. Defects at this stage can only be detected in the very high-frequency range which is covered by AE monitoring.

It has been found that lubrication containing contaminants as small as 500 μm, about twice the size of a dust mite, which would ordinarily be missed using traditional methods, produces an AE pulse, detectible by AE monitoring. This is a clear indication of the usefulness of AE in this area compared to traditional vibrational analysis methods.

Although sources of defects are random in nature, the most important AE source is in the form of cracks, because they produce some of the highest frequencies. Cracks cause a displacement of the surrounding material which increases in magnitude and will usually evolve into more serious problems. It has been shown that vibrational analysis will not pick up defects at this stage, as it is beyond the frequency range. Other aspects of monitoring are arguably just as important as crack formation for the prevention of total failure but usually, occur in the later stages when the damage has already occurred. Being able to detect these early defects is highly advantageous. The table below summarises some common defects that occur in bearings:

 

TYPE OF FAILURE COVERED BY AE MONITORING?
Excessive load – damage to bearings and housing causing premature fatigue/failure. Yes: A change in loading conditions causes an increased output of AE signals.
Overheating – excessive temperatures can anneal the ring and bearing material, redu-cing hardness causing early failure. Yes: Related defects due to loss of hardness, such as deformities.
Lubricant levels and contamination – causes friction contacts and mechanical impacts, respectively. Yes: Increased friction causes detectible strain and mechanical impacts produce sudden releases’ of elastic strain energy. 
Crack formation – early stages of wear as a result of impacts or excessive loading can cause deformation and will evolve to failure.  Yes: Particularly suitable for crack detection as pulses of AE are released in the early stages and can only be detected in the high-frequency range. 

Post-Processing

Unlike VA which requires manual processing of raw data, AE devices process raw data automatically at sensor level. AE devices, such as the Portamonitor®, commonly use algorithms to derive acoustic emission parameters of Distress® and db levels which give an indication of bearing health and overall noise respectively. This provides immediate clarification of defects and is easier to interpret. AE requires approximately 10 seconds of continuous monitoring at a consistent running speed, whereas alternatives typically requires 60 – 120 seconds of measurement to establish the same level of knowledge about the defect. Clearly, AE devices are a time-saving tool - a valuable asset in industry.

Enquire now to find out more about how Portamonitor® will help you.