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Every person that performs vibration analysis develops their own analysis process.  Suggested steps at a minimum should include:

1. Open the spectrum (FFT) and locate the running speed peak and reset the reference speed to that speed.  Since all induction motors vary in speed based on the load,  this is necessary for accurate analysis, particularly at multiples of running speed.

2. Are there any peaks of interest?

3. Where is the primary energy located?
a. Is it sub-synchronous, synchronous, or non-synchronous?

4. Do the waveform patterns support the peaks in the spectrum (FFT)?

5. Remember that defects follow patterns.  Some defects happen at frequencies less than running speed (sub-synchronous) or at running speed or at multiples of running speed (synchronous), or at frequencies greater than running speed but not at whole integers (non-synchronous).

6. Learn pattern recognition and don’t overlook the obvious.

Vibration data collection on vertical turbine

Learn about our vibration analyzers

by Gary James CRL

Compressor Vibration Data Collection
VIBWORKS Vibration Analyzer – Photo courtesy of JetTech Mechanical LLC

In the bustling world of industrial operations, machines are the workhorses, tirelessly powering production lines and driving progress. But just like any workhorse, they need their health monitored to ensure they’re performing at their peak. Enter vibration data—the secret weapon of predictive maintenance. Below are the top benefits of harnessing this data:

  1. Early Problem Detection

Imagine your industrial machines as if they were cars. Just like a car makes certain sounds when something is wrong, industrial machines create vibrations that can tell us if something isn’t right. By collecting and analyzing these vibrations regularly, we can spot small problems before they turn into expensive repairs. This means we can fix things before they break down, saving time and money.

  1. Keeping Operations Smooth and Efficient

Industrial machines are the backbone of operations, and any disruption can send ripples through the entire process. Vibration data helps us ensure that these machines are running smoothly, minimizing downtime, and maximizing efficiency. Monitoring the condition of an asset regularly, whether with a handheld vibration analyzer or a permanently mounted solution, can send warning signals when there are elevated vibration levels so that the plant can make necessary adjustments to make sure everything runs like clockwork.

  1. Enhancing Safety and Preventing Accidents

Safety is paramount in any industrial setting. By monitoring vibration data, we can identify potential hazards before they escalate, preventing accidents and ensuring a secure working environment for plant employees and stopping potential environmental disasters that can affect the surrounding neighborhoods. It’s like installing Automated Emergency Braking (AEB) in a car—a proactive measure to protect the car, the driver, and its surroundings.

  1. Extending Equipment Lifespan

Just as regular exercise can prolong human life, proper maintenance can extend the lifespan of industrial equipment, with emphasis on proper. Vibration data enables us to detect and address issues early, keeping machines in optimal condition. This can also reduce the need for premature replacements, which often lead to infant mortality of rotating equipment. It’s an investment in longevity.

  1. Optimizing Resource Allocation and Decision-Making

Data-driven insights from vibration analysis empower informed decision-making. By pinpointing areas that require attention, organizations can allocate resources effectively, optimizing maintenance schedules and expenditures. It’s like having a GPS for maintenance—guiding us along the most efficient route.

In essence, vibration data is not merely a collection of numbers—it’s a roadmap to operational excellence, guiding organizations toward smoother operations, enhanced safety, and prolonged equipment lifespan. By harnessing its power, industries can navigate the complex terrain of maintenance with confidence and foresight.

Do you archive your historical vibration data or keep it around forever?

by Adam Stredel CRL

Setting the correct lines of resolution (LOR) can sometimes be challenging. In the example below we have a single-stage increasing gearbox.  The gearbox is designed with three individual shafts (input shaft, intermediate shaft, and output shaft), all enclosed within a single gearbox housing.

The speed of the input shaft is constant at 29.93 Hz (1796 rpm) and attached to this input shaft is a pinion gear with 88 teeth.  The pinion gear runs in mesh with a gear with 27 teeth which is mounted onto the intermediate shaft.  This results in a gear mesh frequency of 2633.84 Hz (158,030.4 cpm).  Now we need to determine the required Fmax. Therefore, we simply multiply our calculated gear mesh frequency times 3.25, which gives us an Fmax of 8559.98 Hz (513,598.8 cpm).  In the software, we can’t select the value 8559 Hz, so we’ll need to select the next higher value which results in a Fmax of 10kHz. The next step in the process is to determine what the speed of the intermediate shaft is, and we can do this by using the following formula:

Intermediate shaft speed = 29.93 Hz × 88 teeth = 2633.84 Hz / 27 teeth = 97.54 Hz, or 5852.4 cpm.

Shaft speed diagram

We now need to decide how many lines of resolution we are going to need since in this gearbox we have two closely spaced running speeds.  We have the intermediate shaft speed which is running at a constant speed of 97.54 Hz, and we have the output shaft speed which is variable. When the boiler feed water pump is operated at 100%, we have an output shaft running speed on the gearbox of 94.33 Hz or 5660 rpm.  There is only 3.21 Hz or 192.6 cpm between the two shaft speeds within the gearbox so our lines of resolution setting will need to be set high enough so that we separate them while performing analysis.  With a Fmax setting of 10kHz, we will need to have a minimum of 3200 lines of resolution so we would have two discrete peaks for the two shaft running speeds.

Fmax 10kHz / 3200 = 3.125 Hz, but to be on the safe side I would recommend selecting the next higher resolution setting [6400 line] which will allow a 1.56 Hz [96.3 cpm] resolution which is sufficient to easily see the two different shaft running speeds for accurate analysis.

Below are examples of the resolution, the first not being set high enough (top) and the second with the resolution set correctly (bottom).

Improper resolution settings resulting in a flat top peak for the output shaft speed:

Improper resolution setting for shaft speeds

Correct resolution setting (allowing for the separation of the two shafts turning speeds):

Correct resolution setting for shaft speeds

About Lines of Resolution for Vibration Analysis

by Diana Pereda

Everyone needs phase analysis. A phase study should be performed on problem machines when the source of the vibration is not clear, or when it is necessary to confirm suspected sources of vibration. A phase study might include points measured only on the machine bearings or it may include points over the entire machine from the foundation up to the bearings. The following are examples of how phase can help analyze vibration.

SOFT FOOT

The term soft foot is used to describe machine frame distortion. It can be caused by a condition where the foot of a motor, pump, or other component is not flat, square, and tight to its mounting, or many other things, such as pipe stress, machining errors, bent or twisted feet, and non-flat mounting surfaces. Soft foot increases vibration and puts undue stress on bearings, seals, and couplings. Soft foot on a motor distorts the stator housing creating a non-uniform rotor to stator air gap resulting in vibration at two times line frequency. A good laser shaft alignment system should be used to verify soft foot by loosening the machine feet one at a time. Phase analysis can be used to identify soft foot while the machine is in operation. Measure the vertical phase between the foot and its mounting surface. If the joint is tight, the phase angle is the same between surfaces. If the phase angle is different by more than 20 degrees, the foot is loose or the machine frame is cracked or flimsy. Download our Soft Foot Find-and-Fix infographic which outlines types of Soft Foot including causes and corrections.

Phase Measurement-Soft Foot

COCKED BEARINGS AND BENT SHAFTS

Phase is used to detect cocked bearings and bent shafts. Measure phase at four axial locations around the bearing housing. If the bearing is cocked or the shaft is bent through the bearing, the phase will be different at each location. If the shaft is straight and the bearing is not twisting, the phase will be the same at each location.

CONFIRM IMBALANCE

A once-per-revolution radial vibration usually means rotor unbalance. Use phase to prove imbalance is the problem. To confirm imbalance, measure the horizontal and vertical phase on a shaft or bearing housing. If the difference between the phase values is approximately 90 degrees, the problem is rotor unbalance. If the phase difference is closer to zero or 180 degrees, the vibration is caused by a reaction force. An eccentric pulley and shaft misalignment are examples of reaction forces.

Phase Measurement-Unbalance

LOOSENESS, BENDING, OR TWISTING

Phase is used to detect loose joints on structures and bending or twisting due to weakness or resonance. To check for looseness, measure the vertical phase at each mechanical joint. When joints are loose, there will be a phase shift of approximately 180 degrees. The phase angle will not change across a tight joint.

SHAFT MISALIGNMENT

Shaft misalignment is easily verified with phase. Measure each bearing in the horizontal, vertical, and axial directions. Record the values in a table or bubble diagram. Compare the horizontal phase from bearing to bearing on each component and across the coupling. Repeat the comparison using vertical then axial data. A good alignment will show no substantial phase shift between bearings or across the coupling.

OPERATIONAL DEFLECTION SHAPES

Instead of comparing the phase and magnitude numbers from a table or bubble diagram, operational deflection shape software (ODS) can be used to animate a machine drawing. An ODS is a measurement technique used to analyze the motion of rotating equipment and structures during normal operation. An ODS is an extension of phase analysis where a computer-generated model of the machine is animated with phase and magnitude data or simultaneously measured time waveforms. The animation is visually analyzed to diagnose problems. ODS testing is able to identify a wide variety of mechanical faults and resonance issues such as looseness, soft foot, broken welds, misalignment, unbalance, bending or twisting from resonance, structural weakness, and foundation problems.

Phase and magnitude were measured from permanently mounted X and Y displacement probes on a turbine generator. The values listed in the table were used in ODS software to animate a stick figure drawing of the high- and low-pressure turbine shafts and the generator shaft. The picture to the right of the table is a capture from the ODS animation showing the vibration pattern of each shaft and the relative motion between shafts at 3,600 cycles per minute (turning speed). Many machines vibrate due to deteriorated foundations, looseness, the resonance of the support structure, and other problems that occur below the machine bearings. A phase study might include hundreds of test points measured all over the machine and foundation. Good ODS software can make it easier to analyze phase and magnitude data from a large number of test points. Analysis of an ODS involves observation and interpretation of the machine in motion.

Why Do I Need to Use Phase Analysis?

by Diana Pereda

Vibration Data Collection Compressor
VIBWORKS Vibration Analyzer: Photo courtesy of JetTech Mechanical LLC

Consider how your vibration data collection instrument gathers information. This is a critical factor that can either streamline or prolong the data collection process within your facility. Typically, vibration analysts record and store an overall value (OA), spectrum (FFT), and time waveform (TWF) during each measurement. Some vibration hardware devices require separate measurements for each of these parameters. In contrast, modern day vibration data collectors offer the capability to capture all of these parameters and even more in a single measurement. This technological advancement has the potential to reduce your field data collection time by up to two-thirds. As a result, it not only boosts the performance of your Condition Monitoring team but also provides additional time for advanced troubleshooting methods, ultimately translating into cost savings for your organization.

Watch our Vibration Analysis Know-How: Quick Intro to Vibration Analysis video for a quick introduction to spectra, time waveform, and phase measurement.

The Importance of Vibration Analysis

by Diana Pereda

Vibration Data Collection Compressor
VIBWORKS Vibration Analyzer: Photo courtesy of JetTech Mechanical LLC

When acquiring new vibration equipment, it is important to delve into the genuine long-term cost of ownership, rather than fixating solely on the initial purchase price. The notion that the cheapest or most expensive option is always the wisest doesn’t hold true in this context.

To make an informed decision, it is imperative to account for expenses related to upgrades, support, calibration and servicing of the vibration analysis equipment. Equally critical is to factor in the cost of adapting or upgrading the equipment to evolving needs over time. Here are key questions to ponder, both for yourself and when engaging with potential equipment vendors:

  1. Upgradability: Can the equipment be upgraded, or does it necessitate complete replacement? Is on-site upgrading feasible, or does it require vendor intervention? What are the associated costs?
  2. Scalability: Is it possible to procure the equipment in a scalable manner? Opting for scalable equipment enables cost savings by allowing you to acquire the same device for all employees while customizing the features based on individual user requirements. This adaptability proves financially advantageous in the present and future.
  3. Alignment with Goals: Does the hardware and software align with your facility and corporate objectives? For instance, can the software generate essential matrix reports for tracking improvements over time? Does it adhere to corporate standards for alarms, measurement criteria, and the like? Can it seamlessly integrate with your CMMS software? Is data import from other technologies supported?

These questions are paramount for the sustained success of your reliability program and will ultimately define the genuine long-term cost of owning the vibration equipment under consideration.

Myths and Truths about Vibration Analysis

by Diana Pereda

Technician Mounting KappaX Vibration Sensor on Motor
Kappa X Wireless Vibration Sensor: Photo courtesy of Sensoteq

Selecting the appropriate machines for mounting wireless vibration sensors involves a thoughtful process that integrates criticality analysis and considerations of accessibility. Here’s a more detailed breakdown:

Criticality Analysis

Prioritize critical machines by identifying and prioritizing machines critical to your operational processes. These could be equipment with a significant impact on production, safety, or overall system functionality.

Evaluate the potential consequences of failure for each machine. Machines with higher risks and more severe consequences should be given priority for sensor deployment.

Accessibility

For hard-to-reach areas, where traditional wired setups may be impractical, wireless sensors such as the Kappa X offer a clear advantage. Consider places with limited physical access or spaces that pose safety challenges for personnel. Wireless sensors are also ideal for remote locations reducing the need for frequent on-site visits for vibration data collection.

Additionally, in potentially hazardous environments requiring explosion-proof measures, intrinsically safe wireless sensors provide a secure means for gathering both vibration and temperature data.

Historical Data and Maintenance Records

Examine historical data and maintenance records for each machine. If a machine has a history of recurring issues or maintenance needs, it may be a prime candidate for continuous monitoring using wireless vibration sensors.

By combining criticality analysis with considerations of accessibility, you can strategically select machines for wireless vibration sensor deployment. This approach ensures that the chosen machines align with the overall goals of predictive maintenance, providing valuable insights while maintaining operational efficiency.

5 Benefits of Wireless Vibration Sensors

by Diana Pereda

Kappa X and Pump
Kappa X Wireless Vibration Sensors: Photo courtesy of JetTech Mechanical LLC

One of the largest power plants in the United States experienced issues with two out of three recirculating pumps, which are critical for generating power. Despite regular monthly vibration route data collection, the pumps were running louder than normal, indicating a potential problem. To avoid a complete failure that would halt power generation, the plant implemented continuous monitoring using Sensoteq’s KAPPA X wireless vibration sensor from LUDECA on one of the recirculation pumps.

CHALLENGES

  • Criticality: The recirculating pumps are essential for generating power by providing DeIonized Water (DI Water) to produce steam for the steam turbines. A pump failure would result in a complete power outage.
  • Cost and Lead Time: Replacing a pump was estimated to cost $120,000 and would take approximately 16 weeks, causing significant financial and operational setbacks for the power plant. The ZLD area at which the pump operates is also critical to clean up the pond water to ensure the site also maintains zero liquid discharge from the facility, thus recycling all water and ensuring maximum sustainability of the most precious resource at any power plant, especially in the desert, that being water.

Click here to continue reading this case study and find out what steps were taken to get the project started and the results achieved after implementing continuous monitoring using the KAPPA X wireless vibration sensor!

5 Benefits of Wireless Vibration Sensors

by Diana Pereda

When monitoring the vibration data of a machine, an analyst will want to look at the Time Waveform (TWF) and the Frequency Spectrum or FFT (Fast Fourier Transform) output, as shown below.

Example of Time Waveform and the Frequency Spectrum
Example of a TWF and Spectrum

These two example plots are very useful for determining obvious failure modes, such as, an imbalance with a high amplitude value of Overall (OA) Velocity in the 1 X RPM band or a slippage between two components causing amplitude modulations or beat frequencies visible in the TWF.

For more complex analysis, analysts require further tools to diagnose better the issues. Playing the TWF as an audio file is a good way of listening to the vibration to potentially hear knocking, pinging or high frequency whistling, denoting a problem to further diagnose, as if you were actually beside the machine.

Time Waveform played as an audio file
TWF being played as an audio file

Auto-correlation and circular plots are two other useful techniques applicable to the TWF. Auto-correlation can be useful to remove noisy signals and determining the periodicity or repeating patterns in the vibration signal. The TWF below shows this before and after auto-correlation is applied.

Time waveform before auto-correlation
Before auto-correlation
Time waveform after auto-correlation
After auto-correlation

Finally, an additional step to visualize this better is to perform a circular plot. In the example below the three peaks indicate this application is a pump with three vanes. In this plot view using it can easily determine such failures as a broken fan blade, an imbalance on a vane, or rotor bar issues (if on a motor).

Circular time waveform plot
Example Circular Plot

So as a vibration analyst make sure you use all the tools available to you in your software platform for ease of your analysis.

Thank you Alan McCall with Sensoteq for sharing this informative article with us!

Frequency is Everything!

by Diana Pereda

Machines are like people. They all have certain similarities but are different in many ways. Two exact machines in the same operation may perform and respond quite differently.

Setting alarm values for your vibration measurements is critical for the success of your vibration monitoring program. Alarms will help the analyst identify when conditions on the machine have changed and assist in identifying specific fault conditions. All of this makes the analysis much more accurate and easier. Additionally, this can reduce the amount of time required to analyze the vibration data collected. However, for all this to work the alarms must be set up correctly.

Does the question become what alarm values do you use? Determination of alarm values is especially difficult for the inexperienced analyst, or when no historical data is available for the equipment.  Many sources have published generic alarms based upon specific equipment types and operational speeds. These published alarms can be very valuable in certain circumstances. However, as stated previously, machines are like people and are different in their performance and responses.  The best method is to collect data on the equipment for a period of time and set statistical alarms for each machine based on its unique operating characteristics, performance, and type.

This method will always provide the best results for your vibration program and increase the accuracy of your analysis.

Setting Alarm Values

Check out our VIBWORKS vibration analyzer.

Vibration Alarms Save Time!

by Trent Phillips

Wireless Vibration Sensor

  1. Accuracy: Choose sensors with high accuracy levels for reliable measurements. The Kappa X ensures remote monitoring with data acquisition every minute.
  2. Frequency Range: Ensure the sensors cover the required frequency range. Kappa X offers up to 10kHz Fmax and 6400 Lines of Resolution (LOR) for a comprehensive vibration spectrum view.
  3. Battery Life: Opt for sensors with long-lasting batteries. The Kappa X has a 5-year user-replaceable battery life.
  4. Wireless Range: Check the range and connectivity options. The Kappa X provides a 1,000 feet line-of-sight working distance from sensor to gateway.
  5. Data Storage and Transfer: Evaluate storage capacity and data transfer methods. The Kappa X communicates wirelessly through various gateways, storing data locally and sending it to the cloud based Analytix software.
  6. Durability: Look for sensors designed to withstand harsh environments. The Kappa X is rated IP69K, providing protection against dust, high temperature, and high-pressure water.
  7. Compatibility: Ensure compatibility with existing systems or software. The Kappa X data can be viewed on any device, integrated with routine monitoring efforts, and exported to PLC/DSC via MODBUS.
  8. Cost and Scalability: Consider the cost and potential for future expansion. The Kappa X offers easy installation, no wiring required, and the ability to monitor hard-to-reach areas for comprehensive coverage.

By considering these factors, you can make an informed decision when purchasing wireless vibration sensors that align with your monitoring goals, providing accurate and reliable data for proactive maintenance and equipment optimization.

Wireless Vibration Monitoring: How to benefit from an IoT Solution at your facility

by Diana Pereda

Lines of resolution

Lines of resolution (LOR) describes the number of lines of information that appear in the spectrum (FFT) acquired by the vibration data collector. LOR can be calculated by dividing the overall frequency range collected (Fmax) by the number of lines selected.

LOR represents the amount of detail in the collected data. Without sufficient detail in the collected data, multiple peaks may merge together. This may prevent the correct identification of machinery faults and lead to false conclusions. It is very important that the correct LOR and sensors (accelerometers) be selected for the specific equipment being monitored.

Learn more about our VIBWORKS vibration analyzer.

Setting the proper Lines of Resolution (LOR) is essential for effective vibration analysis

by Trent Phillips

Wireless Vibration Sensor

Wireless vibration sensors like Kappa X offer several benefits compared to traditional wired sensors, including:

  1. Remote monitoring: Wireless vibration sensors can transmit data wirelessly to a central monitoring system, allowing maintenance personnel to monitor equipment performance and detect issues remotely.
  2. Real-time alerts: Wireless vibration sensors can be configured to send real-time alerts via email or SMS text when vibration levels exceed preset thresholds, allowing maintenance personnel to take immediate action to prevent equipment failure.
  3. Flexibility: Wireless vibration sensors can be placed in locations that are difficult or impossible to access with wired sensors, providing more comprehensive monitoring coverage.
  4. Easy installation: Wireless vibration sensors are easy to install and do not require any cabling or wiring, which can reduce installation time and costs.
  5. Improved safety: Wireless vibration sensors can be used in hazardous or hard-to-reach locations, reducing the need for maintenance personnel to access these areas and improving overall safety.

Overall, wireless vibration sensors like Kappa X offer a range of benefits that can help businesses improve equipment performance, reduce maintenance costs, and enhance safety. By providing real-time data monitoring and alerts, wireless vibration sensors can help businesses to implement predictive maintenance strategies and prevent equipment failure, minimizing downtime and maximizing productivity.

Wireless Vibration Monitoring: How to benefit from an IoT Solution at your facility

by Diana Pereda

Trellis Line Graph of Baselines and Alarms for Vibration Monitoring

Importance of Setting up Alarms and Baselines in Machinery Vibration Analysis

Machinery vibration analysis is an essential tool for monitoring the health of industrial equipment. It involves measuring the vibration of machines and analyzing the data to identify potential issues. One of the critical aspects of vibration analysis is setting up alarms and baselines to detect abnormal machine behavior. Alarms and baselines act as reference points for measuring machine vibration. They help identify when the machine is operating normally and when there is a problem. Baselines are established by measuring the vibration of a machine when it is in good condition. The vibration levels recorded are used as a reference point for future measurements.

Alarms are set up to notify maintenance personnel when the vibration levels exceed a predefined threshold. The threshold levels are typically set based on industry standards, manufacturer recommendations, or the specific needs of the organization. By setting up alarms, maintenance personnel can take corrective action before the machine fails, reducing downtime and repair costs.

In addition to detecting problems, alarms and baselines are also essential for trending data. Trending data involves tracking the vibration levels of a machine over time. By comparing the current vibration levels to the established baseline, maintenance personnel can identify trends that indicate changes in machine behavior. This information can be used to predict when a machine is likely to fail, allowing for proactive maintenance.

In summary, setting up alarms and baselines is critical for effective machinery vibration analysis. They provide reference points for measuring machine vibration, help detect abnormal behavior, and are essential for trending data. By using this information, maintenance personnel can take proactive steps to prevent machine failures, reducing downtime and repair costs.

Testing Machines Under Repeatable Conditions for Machinery Vibration Analysis

Testing machines under repeatable conditions is another critical aspect of machinery vibration analysis. To obtain accurate and reliable data, machines must be tested under controlled conditions that can be repeated. This ensures that the vibration measurements are consistent and can be compared over time. When testing machines, it is essential to consider factors such as load, speed, and operating conditions. These factors can significantly impact the vibration levels of a machine. By testing machines under the same conditions, maintenance personnel can identify changes in vibration levels that may indicate a problem. Repeatable testing also helps establish baselines and set up alarms. By measuring the vibration of a machine under controlled conditions, maintenance personnel can establish a baseline for future measurements. This baseline can be used to set up alarms to detect abnormal machine behavior.

Furthermore, repeatable testing can help validate the effectiveness of maintenance activities. By measuring the vibration levels of a machine before and after maintenance activities, maintenance personnel can determine if the activities were successful in reducing vibration levels.

In conclusion, testing machines under repeatable conditions is critical for accurate and reliable machinery vibration analysis. It ensures that vibration measurements are consistent and can be compared over time. This information can be used to establish baselines, set up alarms, and validate the effectiveness of maintenance activities. By using this information, maintenance personnel can take proactive steps to prevent machine failures, reducing downtime and repair costs.

WANT TO LEARN MORE?

Alan Friedman dba Zenco offers machinery vibration analysis courses and certification in accordance with ISO 18436-2. You can see the live course schedule here: www.ZencoVibrations.com/events. You can connect with him on Linkedin. In addition to public classroom training and public virtual courses, Alan is also available for private courses virtually or on-site in addition to informal training and mentoring. Category I and II vibration are also available in Spanish.

Alan, aka the Vibe Guru, has over 30 years of vibration analysis experience, He has trained thousands of students around the world up to Category IV. One of the things that makes Alan a great teacher is his ability to teach people where they are at. Whether you are a math-challenged millwright, an engineer, or a PhD, Alan will challenge you without overwhelming you. If you are interested in condition monitoring you can also check out his book: Audit It. Improve It! Getting the Most from your Vibration Monitoring Program or hire him for an on-site program audit.

Did you know that Alan Friedman left Mobius and is now providing his own courses?

The value of wireless vibration monitoring

by Diana Pereda

Angular MisalignmentParallel Misalignment

Misalignment: High amplitude peaks will appear at 1×, 2×, and sometimes 3× the running speed. Look for a 180° (± 30°) phase change across the coupling in the axial direction (for angular misalignment) or radial direction (for parallel (offset) misalignment). Bearing misalignment (cocked bearing) will cause a twisting motion in the axial direction. Look for a 180° (± 30°) phase change from the top to the bottom of the bearing housing or from one side to the other.

Imbalance

Imbalance: A high amplitude peak will appear at 1× the running speed. Confirm that the phase difference from horizontal to vertical on the bearing is close to 90° (± 40°). The phase difference between left and right horizontal locations should be within 30° of the phase difference between left and right vertical locations. If the phase is unstable, there may be another reason for a large running speed vibration, e.g. looseness or misalignment.

You can investigate the degree of couple imbalance versus force imbalance by looking at the phase difference between the two sides of the machine—if there is little couple imbalance then only a single plane correction may be required to balance the rotor.

Resonance (flexible structures): High amplitude peaks will appear where natural resonance frequencies of the structure coincide with excitation frequencies (e.g. 1×, or other low orders of running speed, blade pass frequency, etc.) Look for a 0° phase change when both sensors are positioned in the same direction between two stationary points. The phase change will be 180° when there is a stationary point between the sensors.

Resonance (variable speed machines): To investigate resonance you can vary the machine speed. A phase shift of 180° will occur as machine speed is increased from below a resonance to above a resonance. A 90° phase shift will be present at the resonant frequency. If a machine is running close to resonance, any small speed variation will cause large phase shifts.

Resonance

Resonance (at a bearing): Look for a change from the normal 90° phase difference in the horizontal and vertical directions at 1×. When a natural frequency is close to 1× in either direction, that phase angle may well be on the way towards its 90° phase change so the two phases may no longer be 90° apart (assuming that the structure has a different natural frequency in either direction).

Eccentric Belt Pulley

Eccentric belt pulley: A high amplitude peak will appear at 1× the running speed of the pulley. Look for a phase change of either 0° or 180° between the horizontal and vertical readings, which indicates straight line motion instead of the usual 90° difference. This symptom is similar to bearing resonance (described above), however, in this case, the direction of maximum vibration will be in line with the two belts.

Mechanical Looseness

Mechanical looseness: High amplitude peaks will show up at many multiples of the running speed, and sometimes even multiples of 0.5× running speed, e.g. 1.5×, 2.5×, etc. Look for fluctuating phase readings at a location from one recording to the next, to the next. Also, compare the phase readings at 30° increments around a bearing housing—the phase will be significantly different at each angle.

Mechanical Foot Looseness

Mechanical foot looseness (soft foot): A high amplitude peak will show up at 1× the running speed. Look for a 90° to 180° phase change between the machine foot and its concrete base. The soft foot may also have a different phase measurement from the other feet.

Learn more about our VIBWORKS vibration analyzer.

Phase Measurement: What is it for? And how you can use it to diagnose failures in 2020.

by Diana Pereda

Order Based Setups

Frequency can be defined as how often an event occurs per unit of time.  A vibration spectrum is displayed as a horizontal and vertical plot (X and Y).  The horizontal (X) axis is the frequency axis and shows a representation of how often an event occurs.  Typically, the vibration analyst may use multiple units of reference for the frequency axis when doing vibration analysis.  The most common units used for the spectrum (FFT) are cycles per minute (CPM) and Hertz.  The least known unit for the spectrum frequency axis is “Orders” or multiples of shaft turning speed.  It is critical to understand the differences in the frequency units (Hz, CPM, and Orders).  It can be advantageous to view data in different units depending upon the machine and the problem being analyzed.

Orders are ratios of frequencies to multiples of a shaft turning speed.  For example, a 60 Hz motor turning 1780 RPM would also have a rotational speed of 29.66 Hz.  The rotational speed would be referenced as one (1) order. Two (2) orders would be twice the shaft turning speed (59.33 Hz) and so on.

Certain equipment defects occur based on multiple of turning speeds.  Looking at data based upon order references can make it easier to remember the specific defect frequencies and identify them during routine analysis.

An order-based analysis is a good way to set up and ensure that the correct frequency range is being monitored for variable speed machines, etc.  You can define your analysis setups in order and be ensured that the correct frequency ranges will be measured by your vibration data collector as the speed of the machine changes over time.

Most modern vibration analysis software and vibration data collectors support order-based data collection and analysis.  If you are unsure, then you should consult the provider of your vibration software and hardware and find out.

Watch our video Vibration Analysis Know-How: Understanding Resonance for a quick introduction to resonance and natural frequencies.

Case Study: Eliminating High Vibration Due to Natural Frequency

by Ana Maria Delgado, CRL

What is the difference between Brinelling and False Brinelling? What causes Brinelling and False Brinelling?

Brinelling

Brinelling is named after the Brinell scale of hardness.  In the Brinell hardness test, a small ball is pressed into the surface of a material using a specific amount of force. The size of the indentation that occurs in the material is a measure of its hardness. Brinelling is an indentation in the surface of a material; a permanent plastic deformation that occurs when the yield strength of the material has been exceeded.

Brinelling

Brinelling can occur in rolling element bearings when large static loads cause the balls or rollers to create indentations on the race; usually spaced the same distance apart as the balls or rollers. It can also be caused by a single impact or a repeated impacting. The main point is that the forces of the balls against the race exceed the yield strength of the material and result in a permanent dent. These excessive forces may occur during transportation, in storage, or during the bearing installation process. Special care must be taken when pressing or clamping bearings to avoid causing damage.

False Brinelling

False Brinelling in a stationary bearing creates a similar pattern of marks on the race separated by the distance between the balls or rollers. This wear pattern is called “fretting.” False Brinelling occurs when vibration pushes the oil out of the contact surface between the balls or rollers and the race. The loads in this case are not enough to cause permanent damage or indentations in the race, but the polishing of the race surface causes it to look like Brinelling – hence the name “false brinelling.” Because the races are polished by surface-to-surface contact in the absence of oil but are not actually damaged, the wear pattern will disappear after a short break in period.

False Brinelling

False Brinelling in a stationary bearing often occurs during transportation of bearings or when they are in storage if they are subjected to vibration from trains or forklifts passing by or other sources of vibration. It is also common in standby machines if they are not isolated from the vibration coming from other machines running nearby.

It’s also possible for false brinelling or fretting to occur in rotating bearings if the rotational speed causes the balls or rollers to make contact with only specific parts of the races over and over again. This causes a similar wear pattern however in this case the distance between the wear marks will not match the distance between the balls or rollers.

Take Care of Your Bearings!

The proactive approach to bearing care includes being careful about how bearings are shipped, stored, and installed. Brinelling and False Brinelling can be avoided by using correct packaging, rotating stationary shafts, and storing bearings in cabinets that are mounted on vibration isolators and that have damping material on the shelves.

WANT TO LEARN MORE?

Alan Friedman dba Zenco offers machinery vibration analysis courses and certification in accordance with ISO 18436-2. You can see the live course schedule here: www.ZencoVibrations.com/events You can connect with him on Linkedin. In addition to public classroom training and public virtual courses, Alan is also available for private courses virtually or on-site in addition to informal training and mentoring. Category I and II vibration are also available in Spanish.

Alan, aka the Vibe Guru, has over 30 years of vibration analysis experience, He has trained thousands of students around the world up to Category IV. One of the things that makes Alan a great teacher is his ability to teach people where they are at. Whether you are a math-challenged millwright, an engineer, or a PhD, Alan will challenge you without overwhelming you. If you are interested in condition monitoring you can also check out his book: Audit It. Improve It! Getting the Most from your Vibration Monitoring Program or hire him for an on-site program audit.

Did you know that Alan Friedman left Mobius and is now providing his own courses?

by Ana Maria Delgado, CRL

Wireless Sensors mounted on machine

Wireless vibration sensors have their place in a good reliability program and can benefit the maintenance team’s ability to monitor machine health reliably. When choosing a wireless vibration sensor, the battery life is a key parameter in its selection. Designers and manufacturers should perform battery capacity models to be confident in the performance and battery life alongside actual current consumption measurements.

When creating a battery capacity model to determine battery life within a wireless sensor, there are several main considerations:

  1. Battery chemistry: The type of battery chemistry used in the device can greatly impact the battery life. For example, lithium-ion batteries have a higher energy density than nickel-cadmium batteries and therefore can last longer. However, Lithium Thionyl Chloride (LTC) has a stable voltage over time and high current pulse capability for wireless transmissions. It also performs better over temperature than Lithium-ion.
  2. Battery capacity: The capacity of the battery is an important factor in determining battery life. A larger capacity battery will last longer than a smaller capacity battery under the same usage conditions. However, the larger the capacity, the larger the physical dimensions, so there needs to be a balance between the overall size of the sensor (& mass) and its application constraints.
  3. Operating conditions: The operating conditions of the device, such as temperature, humidity, and usage patterns, can greatly impact the battery life. The temperature being the biggest impact, since the sensor may have a wider operating range of -40⁰C to 80⁰C.
  4. Battery age: As batteries age, their capacity decreases, so the model should add this parameter as a %.
  5. Energy consumption: This can be the difficult part, as it needs to consider all the different operating modes of the sensor, such as sleep, measurement, and wireless transmissions. Each mode will consume different amounts of energy and for different durations. These duty cycles can be worked out over a fixed period of time and input into the model.
  6. Self-discharge rate: Batteries have a self-discharge rate over time, which means they lose capacity even when not in use, the model should take that into account in order to accurately predict the battery life. Battery chemistry has an impact on this too.
  7. Quality: The quality of the battery is important, manufacturers often have different quality standards, so it’s important to consider the quality of the battery being used in the model to make accurate predictions. As a product used in the reliability world, we need to rely on the sensor, easy to maintain, and of a high standard.

When performing actual measurements, multiple samples should be used and preferably samples from different manufacturing batches. This ensures that any production tolerances are understood. Testing over temperature and with different % depletion of batteries can give a good spread or standard deviation of the current consumption over life. Taking both the model and measurement inputs will give a solid indication of the battery life of your wireless sensor. In your condition monitoring or reliability program if you are planning on using wireless vibration sensors, please consider the above points in determining their battery life.

Thank you Alan McCall with Sensoteq for sharing this educational article with us! 

by Diana Pereda

Vibration data collection

 

Vibration Route Frequency

How often do you collect vibration data on your equipment?  Is it monthly, quarterly, or even yearly?  Most of the time management will allow data collection frequencies based upon the importance they assign to vibration analysis or available resources at the time.  Management may ask that vibration data be collected every month or even more frequently if the machine has failed recently.  Different companies and managers use different means to determine how often to collect vibration data or any other CM data for that matter.

Assigning arbitrary data collection frequencies (routes) to your equipment may do your reliability efforts a disservice.  The best method is to determine the failure intervals of the failure modes (bearing defects, etc.) in the equipment.  Assign data collection intervals short enough to identify these failures.  For example, a bearing may develop a failure on day one and run for ninety days before it causes the machine to fail.  If the machine is monitored with vibration analysis every ninety days, then your analyst may never identify the bearing failure condition in the machine.  The result is that your machine will most likely fail without anyone being aware of the issue.  If the same machine is monitored monthly with vibration analysis, then the bearing failure condition would most likely be identified with your vibration monitoring program.  This would alert the maintenance department of the issue and allow appropriate repair efforts to be budgeted and scheduled.

Watch our Reliability Matters: What Can I Do? video to learn the benefits of vibration monitoring to keep your equipment running efficiently.

Vibration Data Collection Pitfalls

by Trent Phillips

All electric motors can develop electrical and mechanical problems over time in operation. One common failure mode is caused by the motor’s stator being eccentric. Stator eccentricity problems will produce an elevated peak at the two times the electrical line frequency (2×LF) which in the United States is 120 Hz (7200 CPM.)

Stator eccentricity problems produce an elevated peak at the 2 times the electrical line frequency (2×LF) which in the US is 120 Hz (7200 cpm.)

The root of the problem is excessive stator eccentricity which results in an uneven air gap between the rotor and the stator.

For induction motors, this eccentricity shouldn’t exceed 5% and for synchronous motors, it should not exceed 10%.  All electric motors will produce some vibration at the 2×LF, however, it is recommended that the cause of an elevated 2×LF peak be investigated for amplitudes exceeding 0.1 in/s peak for motors that are already in service.

There is another cause which is mechanical in nature which also produces increased amplitudes at the 2×LF and is commonly known as “Soft foot”. The existence of a soft foot condition in a motor will cause the frame to become distorted when the foot bolts are tightened and will ultimately lead to premature bearing failure.

Soft foot increasing amplitudes at the 2×LF

A machine is determined to have a soft foot condition if the machine frame deflects by more than 0.002″ – 0.003″ when any machine foot is tightened or loosened while the other machine feet remain tight. This deflection produces an internal misalignment of the bearing bores, leading to shaft deflection, and will greatly increase the radial loading on the bearings, which in turn will lead to premature wear and failure.

Fortunately, the procedure for checking for soft foot is easy to perform using modern laser alignment systems and feeler gauges. Another method for checking soft foot on a motor that has been placed back in service and cannot be shut down is called a running soft foot check.

The first step to performing this check is to utilize a vibration analyzer that can stream data live. This is a feature certain vibration analyzers have which allows the user to continuously monitor the vibration spectrum while the machine is running.

CAUTION – This procedure requires “Extreme Caution”* since loosening a foot will most likely affect the shaft alignment. It is critical that only the foot being checked be loosened while all remaining machine feet remain tight. *See important note below

While the vibration analyst monitors the live vibration spectrum, one foot at a time is loosened (always with the other feet tight!) and then retightened. The best way to accomplish this check is to have a coworker loosen and then retighten each machine foot as the vibration analyst monitors the vibration spectrum. This process is then repeated until each of the machine feet has been checked.

The user will usually see a significant drop in the 2×LF amplitude and will also notice a change in the sound of the motor once the problem foot (or feet) have been loosened.

*Important Note: We mention this procedure for informational purposes since the practice is not uncommon throughout the industry. However, LUDECA does not advocate for this procedure given the safety risks involved.

Q&A Webinar: Detecting Misalignment using Vibration Analysis

by Diana Pereda

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