The use of a strobe light or stroboscope is another tool in the toolbox of the analyst in the field of Reliability. This tool can be used for a variety of purposes including checking or verifying the rotational speed of a component if the shaft or coupling is accessible.
The user can inspect it without stopping or shutting down the equipment. If the model of stroboscope the user has is capable of being triggered from an external source for the flash rate the user can move the flashing strobe around the machine’s moving parts to see which one appears to stop which can indicate that this is the source for the triggering and therefore the source of vibration.
Most stroboscopes have an output that can send a signal to a vibration instrument to be used as a tachometer input to the instrument. Dynamic balancing can be performed using a stroboscope instead of a laser, optical or infrared tachometer.
A key safety consideration is that one must remember when utilizing a stroboscope that rotating structures (such as shafts or couplings) only appear to be frozen or stopped when the stroboscope flash rate is synchronized to the same frequency as the shaft’s rotational speed.
People who are not familiar with stroboscopes have reached out to touch what appears to be a stopped shaft and become seriously injured. When using a stroboscope and the machine has not been started the user can use a marker and place a horizontal mark on one side of the shaft and a vertical mark on the opposite side so when the machine is running and you adjust the internal oscillator in the stroboscope to match the rotating shaft’s frequency you will either see a vertical or a horizontal mark; if you see a plus sign then the flash frequency is either half or double the shaft frequency.
by Diana Pereda
A balancing tool is simply anything that serves the analyst for the purpose of statically or dynamically balancing a rotating piece of machinery.
Precision balancing should include:
- An instrument capable of reading data from different types of vibration sensors, including accelerometers, velocity sensors, and proximity probes among others.
- It should also be able to display the rotational speed of the machine and the phase angle of the unbalance. The instrument should have a tachometer or a stroboscope input to measure a target on the rotating component indicating the rotational speed in CPM/RPM/Hz.
- The analyst would also need to have a way of measuring the exact amount of weight that they may need to add or remove from the rotor for the purpose of balancing and a way of attaching those weights. These could include clamping with set screws or bolts, bolts and washers, welding of plate material, and here care must be taken to ensure the metallurgy of the machine is not compromised.
- The instrument the analyst is using should include a software program that the analyst is familiar with. The time to learn a balancing program is not in the field while trying to perform a balancing job. If the analyst does not have a program for balancing he or she should be able to graphically plot out the balance solution as necessary. This approach is usually slower and more error-prone.
- The cables that connect the sensors and the tachometer to the instrument should be of adequate length to be safely installed. There should also be thought about how to attach the sensors and tachometer to the equipment so they do not become detached during the balancing process.
- The analyst should also have a way to document the balancing process.
To help you implement balancing at your facility, download our 5-Step Balancing Procedure a simple and effective procedure for doing field balancing!
by Diana Pereda
While in Louisville, KY after the #SMRP19 conference, I took a tour of the Angel’s Envy bourbon distillery and was thrilled not only by their fine bourbon finished in port wine barrels but by their attention to safety and unique promotion of safety all around their clean facility. Their clever “Heaven can wait. Safety first” statement obviously applies to all maintenance activities but in this particular case, shown in my photo, it was used to emphasize the importance of lock-out and tag-out procedures, also known throughout our industry as LOTO.
Unlike ultrasound testing, acoustic lubrication or vibration analysis, all of which check machine or facilities condition while up and running, alignment and balancing require machines to be shut down and properly locked out, to adhere to all safety regulations. Only then can the components be mounted on the shafts. This ensures the safe rotation of the shafts and alignment corrections to be made without risk of injury to maintenance personnel.
I can’t stress enough the importance of safety during service or maintenance of machines and encourage you to develop more ingenious slogans like “Heaven can wait. Safety first” to draw more attention to this important concern within your plant.
Here are the six steps to follow for proper LOTO per OSHA 3120:
1. Prepare for shutdown;
2. Shut down the machine;
3. Disconnect or isolate the machine from the energy source(s);
4. Apply the lockout or tag-out device(s) to the energy-isolating device(s);
5. Release, restrain, or otherwise render safe all potential hazardous stored or residual energy. If a possibility exists for reaccumulation of hazardous energy, regularly verify during the service and maintenance that such energy has not reaccumulated to hazardous levels; and,
6. Verify the isolation and deenergization of the machine.
A personal note for Bourbon lovers: if you haven’t already, try pairing dark orange chocolate with your favorite bourbon, what a delicious combination! Heaven can wait. Please drink responsibly.
by Ana Maria Delgado, CRL
There are a lot of aspects that need to be taken care of in condition monitoring. Field balancing is one of those. There are two types of balancing: static and dynamic. The first one deals with balancing in a controlled environment and another one is balancing a piece of equipment in the field under field conditions. When you have balanced an asset against a number of parameters, you know when there’s an unbalance in the equipment. There are different defects that can be caught using a balancing frequency or other parameter. There are a lot of causes for unbalance such as corrosion, part damage, assembly error, and other machining tolerance errors.
The equipment that we need in the field includes: a balancing tool—whether it’s traditional or some modern device—that does the job of balancing the machine. When you are evaluating a machine, you can run different analyses to know what needs to be done to fix the unbalance found in the machine. The standard procedure could be a process starting with calculating the amplitude of the unbalance, then coming up with a correction weight that can be attached to the piece of the equipment to balance the machine. You can try this method until you get the desired results. Download our 5-Step Balancing Procedure – A simple and effective procedure for doing field balancing.
There are some standard specifications provided by ISO based on rotor weight and rpm of the machine. These provide general guidelines to check the balance of the machine but you can decide the specifications based on the evaluation of the rotor. When you are in the field, removing weight accurately is quite hard. It is very difficult to determine the exact weight you have taken out. Adding weight and keeping track of it is comparatively easy. Any person looking to start in field balancing should start with learning about graphic balancing and studying the tools.
Going with a proper alignment training course and field balancing training course would be the best choice, where you can learn to understand the problem, get to know the right tools, and learn from understanding the graphical examples. Customers always want to know the type of weights that you have used, their position, and how they are balancing the machine, so you should have that information at hand in the field. The technicians should know the resonance against different frequencies so that they can capture the right data and make decisions based on that to fix the issue right away.
A given piece of equipment doesn’t always need weight to balance it. Sometimes cleaning a dirty piece of equipment goes a long way. You have to make sure that the equipment is clean before you go about balancing the machine. You have to pay attention to your machine data, see what it is telling you, and then make an informed choice to eliminate the defects. You have to start with laying the groundwork first, like checking for soft-foot or rust that can throw off your readings. The best way to get it done is to let the programmers and providers work together to make necessary enhancement towards better field balancing.
Hear more from Gary James in this podcast by James Kovacevic and learn more about static & dynamic balancing differences, knowing resonance against different frequencies, and his advice and knowledge of field balancing.
by Diana Pereda
Sometimes unbalance can be caused by a shaft key being too long. When a shaft assembly goes to the balance machine, the assembly is normally balanced with a half key installed. The coupling and key have been removed and a half key installed into the keyway on the shaft. The straight portion of the shaft keyway is filled with a piece of steel; however its height is ground down so that it closely matches the outer radius of the shaft. In other words, it doesn’t stick out!
Electrical tape is then wrapped around the half key and shaft so that the half key doesn’t come flying out during the balancing operation. After the rotating assembly has been successfully balanced to within tolerance, the rotating assembly is returned to the technician for final reassembly.
In the following example, let’s assume that the actual length of the keyway in the shaft is 8 inches long and 3/8″ deep. The length of the coupling hub keyway is 4 inches long and it is also 3/8″ deep. If the technician installed a key that measured 8″ long × ¾” × ¾” and then mounted the coupling onto the shaft it would result in an excessive key length sticking out past the back edge of the coupling hub. The extra 4 inches × 3/8″ high key stock sticking out behind the coupling could be enough mass to cause the imbalance to exceed ISO balance tolerances.
The following method should be used to calculate the proper key length:
Source: Practical Solutions to Machinery and Maintenance Vibration Problems, Chapter 5, Unbalance, Section 16, Unbalance Due to Assembly Errors – Key Length Considerations by Update International
Our advanced field balancers can help you identify, correct and avoid the unwanted consequences of equipment unbalance. For more information, visit our website.
by Ana Maria Delgado, CRL
Vibration is everywhere! Vibration is a “back and forth” movement of a structure or component. Vibration can also be referred to as a “cyclical” movement. It can be inherent in a piece of equipment or can be induced by another form of energy. The real question is whether the vibration is detrimental to the equipment and its internal components.
Vibration is typically monitored through some form of analyzer, either online or offline such as the VIBWORKS analyzer.
What causes vibration? Here are just a few causes, but there are so more which can lead to elevated vibration levels. More importantly, if caught early enough, they can be corrected and thereby maximize the life of our equipment:
- Installation of the machines
- An improperly mounted bearing can cause severe vibration. This can lead to damage of the bearing as well as other components within the machine.
- Operation of the machine
- Pushing our machine beyond its recommended maximum output. Our machines respond by vibrating more than the recommended allowable limits and will eventually fail.
Watch our video ‘What’s Misalignment’ to learn more about the causes and effects of having misalignment in your rotating equipment
Some common machine problems that generate mechanical vibration:
- Misalignment is one of the most common issues that leads to high vibration and eventually failure of the machine. It can be easily detected and corrected. Take the time to laser align machines properly to the recommended tolerance.
- Unbalance is another easily missed problem that causes severe damage to our equipment. It can also lead to cracks of the housing itself. If not detected and corrected soon enough it can lead to dangerous catastrophic failure. Unbalance can be easily detected and corrected extending the life of equipment.
We never have enough time to do things right the first time but always find time to do them again.”
These few issues can be easily detected with properly set-up software. Often, the setup is incorrect and inaccurate. Invalid data is captured in the FFT. Please consult an expert to make certain you are utilizing your condition monitoring software to its fullest potential. Remember… If it’s Critical and Rotates it should be Aligned, Balanced and Monitored.
by Ana Maria Delgado, CRL
Just what does it take to be successful at balancing? Let’s start with some basics. First you need to have an understanding of the balancing process, next nomenclature: is it unbalance, imbalance, out of balance, or what? Use a consistent description and stick with it. Next, think about what the source of unbalance could be: is it uneven wear on parts? Voids within castings? Damage from impacting? Material buildup? Even though buildup is not usually a problem, when it begins to come off it rarely does so evenly thus creating an unbalance. In other words, unbalance is simply the uneven distribution of mass.
Simply review or collect data to ensure that the undesirable vibration is from unbalance and not some other issue such as a belt problem, misalignment, electrical issue, etc. Once you’ve determined that the vibration is indeed unbalance you need to inspect the object to be balanced. If it is not clean, clean it. Look for damaged or broken parts. On belt driven equipment inspect the belts as their frequency can be very close to running speed and can hinder the balance job. Make sure you have the proper tools for doing the balancing job, such as a balancing instrument capable of reading the vibration that is produced at running speed or what is commonly referred to as 1×or 1 times and capable of indicating the phase angle at 1×. This could involve utilizing an optical tachometer, laser tachometer, magnetic pickup or even a stroboscope. Some tachometers will require a piece of reflective tape on the shaft for the tachometer to read from and this might require stopping the machine if still in service.
Tip: I try to place the tape horizontally, or along the axis of the shaft, with the leading edge of the tape on the trailing edge of the key way. This can be helpful if you ever have to return for another balancing job on the same machine. You need to determine if you will be adding or removing material in order to balance the rotating component. If removing material, how will you determine how much you’ve removed;if adding weight, you need to make sure the weight you are adding is of a material that is compatible with the service the machine is exposed to. If adding material “weights”, how will they be attached? With set screws? Bolts? Clamps? Welded on? All this should be considered. One last tip: if after two runs you’re not there or almost there yet, you might need to stop and examine your process to ensure no mistakes have been made.
Download LUDECA’s 5-Step Balancing Procedure.
by Gary James CRL
As Published by Maintenance Technology Magazine September 2017 issue
If greater reliability and uptime are of any concern to you, then precision maintenance is a key component in achieving it. This means having clear and simple, yet meaningful, procedures in place for the different tasks involved. Two such tasks are precision alignment and balancing. LUDECA’s 5-Step Procedures will help guide your facility and maintenance staff to achieving precision maintenance.
The alignment and balancing procedures lay out the basic steps required to align and balance machines safely, reducing risk of injury and increasing likelihood of a quality outcome. Checklists simplify the workflow and serve to remind employees of the processes required to consistently and safely perform the precision maintenance task.
Well-aligned and balanced machines run more reliably, with a greatly reduced probability of failure. This allows for better maintenance planning, greatly reduced repair and maintenance expenses, increased uptime and more profits.
A good alignment procedure ensure that machines are aligned to the proper tolerances for the running condition of the machines, taking into account such things as thermal growth and anticipated positional changes. This ensures that the greatest efficiency is achieved in your running machinery, prolonging their health and reducing power consumption. Studies have shown that well-aligned machines result in a 3% to 10% reduction in power consumption. Noise and heat generation is reduced, producing a safer work environment.
- Production Quality
Good alignment and balancing result in better product quality since vibration is minimized, resulting in a more uniform and higher product quality. Unexpected breakdowns in production machinery may lead to costly waste from scrappage and high restart costs for the production line.
- Training & Procedural Consistency
Once implemented, a procedure ensures all employees involved in the activity face clear and consistent expectations and processes, leading to a better understanding between all staff in the facility. Training expense can be reduced since often only refresher training is required to update understanding of the technology utilized as updates are rolled out. Records should be kept that document employee training.
The next step in precision maintenance and reliability is the Implementation of formal specifications that detail every step in a task from safety to activity process to documentation, to ensure that anyone involved can follow the procedures and guidelines without confusion, and reach the desired outcome for all machinery types in the plant. Such specifications typically take from two to three months to develop and a further two to three months to roll out and fully implement. LUDECA has written a number of these specifications for customers worldwide. Let us help you as well.
by Alan Luedeking CRL CMRP
Guest Post by Bob Dunn from I&E Central, Inc.
A customer was having difficulty balancing the rotor shown above. They had made multiple corrections, some contradictory, and were worse than when they started. In that this is on a shop stand and controlled conditions, something was not right. Looking at the photo, I saw a couple of likely issues.
- The shaft is pretty reflective itself, it is doubtful that they were getting a good or consistent phase reading. I recommended they put a ring of black tape on the shaft, with the reflective tape on the black.
- The tach sensor is pointing at the shaft at about a 90 degree angle. Optical sensors and reflective tape works better if the sensor is aimed at an angle – 30 degrees or so.
- The tach sensor is pretty close to the rotor. In this case it is not too close, but you can be too close. A sensor like this will work from several feet away, if you are having problems, try moving the speed sensor further away.
The customer applied the tape and adjusted the tach position. The rotor was balanced in a single run.
by Yolanda Lopez
Proper equipment function requires a properly aligned and balanced machine. Allowing a machine to operate with an unbalance condition can result in bearing damage, cracks, loose components and many other costly maintenance issues. Loose debris can dislodge and impact the balance quality of a machine. Debris buildup on the impellers/blades, and other rotating parts can create unbalance conditions. Before balancing the machine it is very important that the rotating surfaces (blades, etc.) are cleaned of any debris. Removing buildup will help ensure that the machine can be properly balanced and remains in a balanced condition.
by Trent Phillips CRL CMRP - Novelis
The practice of reliability has many tools, processes and methodologies that can and should be implemented within a facility. Try as we may, it is usually not possible to implement and sustain all of them. So the challenge quickly becomes deciding which aspects of reliability to implement and in what order!
Implementation and enforcement of standardized work procedures is a very critical aspect of reliability and should be at the very top of your list of required reliability tools! Standard procedures focusing on fundamentals such as proper torquing, alignment, balancing, bearing installation, and equipment installation, should be in place. In addition, standard procedures for work request, work approval, planning, scheduling and work execution should be implemented as well.
Make sure that standard procedures are in place to execute the reliability methodologies at your facility. Otherwise, your site may always find it difficult to achieve sustainable and best practice maintenance and reliability.
Why? Unfortunately, people are usually the biggest obstacle we face in our jobs. People do not like to change, forget or misunderstand what needs to be done. Standard procedures will help ensure that reliability processes are routinely followed and things do not fall backwards to the unreliable way they have always been done. Additionally, it will provide the ability to track how well your facility or company is doing at implementing, executing and maintaining the reliability practices desired.
by Trent Phillips CRL CMRP - Novelis
- Right safety procedures before you balance.
- Right machines to balance.
- Right balancing procedure.
- Right balancing tool.
- Right balancing tolerances ISO or API.
- Right data collection
- Right weights.
- Right weights locations.
- Right corrections.
- Right balancing report.
Download [Infographic] 5-Step Balancing Procedure
by Ana Maria Delgado, CRL
Precision balancing is an essential part of a proactive reliability program as it can eliminate many machine failures and defects. This Infographic outlines an easy and effective way to balance your rotating equipment.
by Ana Maria Delgado, CRL
In today’s world, video platform is the way to accomplish effective visual knowledge and a learning mechanism in many organizations. With the use of video, one not only is able to promote products and services but one can also strengthen a culture and demonstrate how-to scenarios easily and quickly.
LUDECA believes in communicating visually to help customers educate and train their personnel on precision skills. For this reason, we are pleased to announce the release of our new microsite www.LudecaVideos.com, which features a Shaft Alignment Know-How series plus a Know-How series for Vibration Analysis and Balancing. The video site features basic terminology, fundamental concepts, advanced measurements as well as product demonstrations. The videos are indexed by category but also searchable by keyword.
We felt there was a need to go back to basics and help educate on precision skills and related technology to improve asset reliability. Following the Uptime Elements™ holistic approach to reliability, alignment and balancing are key components of your asset condition management (ACM) program. We are happy to offer these videos to our customers for their personnel to access and for use in their training programs. We hope this content assists them and others in either improving their reliability program or in getting one started and leads to world-class reliability programs,” —Frank Seidenthal, president of LUDECA.
We encourage you to visit www.LudecaVideos.com and see for yourself the value behind each video.
by Yolanda Lopez
The following blog relates to those who field balance using a photo or laser tach and reflective tape.
By far the most common pitfall to field balancing is a problematic tach signal. When one balances a rotor using one’s field balancing unit (VIBXPERT II, VIBXPERT or VIBSCANNER) the equipment is recording the energy displayed at the frequency of the signal from the tachometer. To help visualize the importance of a clear tachometer signal that is exactly 1 pulse per revolution, look at figure 1.
What amplitude will your equipment record if the tach pulses:
1. 1,195 times per minute?
2. 2,002 times per minute?
3. 2,006 times per minute?
4. 2,011 times per minute?
5. 2,013 times per minute?
We often start a balance job by haphazardly placing our tach and tape. Because both the tach and tape are well engineered, we may go on without a problem. But just a little attention to some of the common tach signal problems is usually all it takes to avoid having to restart a botched attempt at field balancing. What should be avoided when setting up a tachometer?
1. Don’t place your tach too close to the rotor. Most tachometers used in the field work by sending some type of light out and bouncing it back, so they have a sending function and a receiving function. The wavelength of the light is such that not just any light will be accepted by the receiver, but only that wavelength of light sent out by the sending unit. So the receiver counts a pulse every time that wavelength of light appears (or disappears, depending on whether you are triggering by leading or trailing edge). The receiver is no smarter than that, we must supply the rest of the intelligence. When we put the receiver too close to the rotor, even a poor reflector may be able to bounce back enough of the light signal to create a pulse. The balancing technician should determine the distance from the rotor to set up their tach with the understanding that they want a good signal bounced back from their chosen reflector, AND ONLY THEIR CHOSEN REFLECTOR! Most often, a 6 inch space is sufficient.
2. Don’t place your tach pointing perpendicular to the rotor. Earlier we stated that “both the tach and tape are well engineered”. One thing most of us field balancers take for granted is the reflective tape. This tape is actually a well-engineered tool. Reflective tape is faceted in such a way that light can strike it at an acute angle, and still be reflected right back along the axis from which it came. This allows the tach to be staged at such an angle that light will strike the rotor, even a rotor that is itself a good reflector, and be reflected off and away from the receiver UNTIL the tape comes into the line of the light, and then with its special faceting, it will bounce the light back to the receiver. This gives one clean pulse every time the tape comes around, and only when the tape comes around.
3. Don’t use old reflective tape that may not be in proper working condition. Make sure the tape is clean and in good shape. Reflective tape works very well when it is clean and in like-new condition, but can get dirty or even deteriorate if conditions are right. Replacing a small piece of tape is most often very quick, easy, and cheap compared to extra balancing runs or possibly even worse.
4. Don’t use a tach with dirty lenses. Make sure the tach lenses are clean and in good shape. When your lens is dirty, it forces you to do things (in order to get a strong enough signal to go through the dirty lens) that aren’t conducive to a clean, clear, once per revolution pulse; like move the tach too close to the rotor, or place it at a 90° angle to the rotor.
Doing everything we have suggested here could take all of 5 minutes (if you work slowly) at the beginning of a field balance job, but it could save a lot!
by Mike Fitch CRL
Recently I visited a customer’s facility to provide onsite training for the VibXpert vibration data analyzer they had recently purchased. Before we could get started collecting data, we needed to build the equipment hierarchy and measurement templates required. Once the database was created, we loaded routes into the VibXpert and proceeded to collect vibration data.
The first room we entered had two large belt driven overhung fans. At first glance it was obvious that one of the fans was running extremely rough. We collected vibration data on both fans and paused to review the results. We noticed that the 1× amplitude on the rough fan was over 1.0 inches per second peek. The local CM technician immediately commented that the fan should be balanced and his observation was correct when simply looking at the vibration data.
The room was full of clues which explained the cause of the fan unbalance. This facility processed and manufactured wood products. Large amounts of wood dust are produced and these fans were designed to ventilate a high dust area. Everything in the room was covered with wood particles and dust. The only question was how much had accumulated on the inside of these fans.
I asked if the fan could be stopped for a short period and the inspection door opened. My request was honored and the fan was shut down and locked out. Our examination revealed the fan blades had amassed substantial amounts of wood particles. The fan blades were cleaned and resulting in a pile of wood chips weighing about 5 lbs. The fan was placed back into operation and allowed to run for several minutes. Vibration data was recollected on the fan and the 1× amplitude had reduced to 0.1 inches per second.
Fans require corrective action to eliminate unbalance conditions from time to time. However, the cause of unbalance may simply be buildup of foreign matter on the blades. This fan was being allowed to beat itself to death due to product buildup. This facility learned a few lessons from the experience. First, inspections utilizing the human senses (touch, hearing, etc) could have been used to determine that this fan was in need of attention. Second, periodic vibration monitoring would have identified a need for maintenance on this fan. Third, if a fan is properly balanced, simply cleaning foreign matter buildup may reduce the vibration, prevent equipment damage and maintain the reliability of the equipment. Make sure that you utilize these three steps during your daily maintenance efforts on equipment.
by Dave Leach CRL CMRT CMRP
I have been using the VIBXPERT II Balancer for a year. I have balanced fans ranging in size from 10, 000 to 1 HP, mostly within 3 shots. My last customer had a contractor quoting a fan rotor replacement. Using the VIBXPERT II, the fan was balanced to 2 mils from 25 mils in 3 shots. The customer cancelled the fan replacement. The ability to acquire and view spectrum, review cost down data, and perform resonance testing are features not found in other balancers. —Victor Galanto, Fan Services Associates
by Ana Maria Delgado, CRL
If you want to find the secrets of the universe, think in terms of energy, frequency and vibration.” ? Nikola Tesla
Could Tesla’s secret be the energy wasted due to vibration at a frequency equal to shaft speed all caused by rotor unbalance?
Balanced rotors are critical for achieving production and profit goals. Unbalance creates high vibration, which leads to other faults resulting in decreased machine life, wasted energy and reduced efficiency. Smooth-running machines are required for producing products that meet customer specifications. The IOSR Journal of Mechanical and Civil Engineering states that rotor unbalance is the major cause of vibration problems. A good balancing process is essential for successful physical asset management.
Read my entire article Field Balancing Rigid Rotors at Reliable Plant.
by Bill Hillman CMRP
As more and more wind turbines are coming out of warranty, the industry is focusing on making sure that the assets they have in place are in proper running form. If it is the gearbox, the generator, and/or the rotor blades, they need to be inspected and/or checked.
In the case of the rotor blades, if they have had any sort of work performed on them such as repairs after lightning strikes, moisture in the blade, removal and/or addition of coating on the blades, etc. It is good practice to check the mass unbalance. By checking mass unbalance first and then performing the balance job, this will constrain the vibration levels to acceptable tolerances such as the VDI 3934. It will also help reduce the amount of wear on the rolling elements and gears.
by Alex Nino CRL
Is your equipment considered a slow running speed machine? If so, what speed do you consider slow? Is it 30 RPM? 60 RPM? 100? 200? 600?
No matter what you consider slow speed, the two most critical points to consider for slow running equipment are:
1) Does your vibration sensor (accelerometer) have the appropriate frequency range to measure low frequencies?
2) Does your vibration analyzer and/or online monitoring system measure down to those frequencies?
Unfortunately, some vibration analysis devices on the market are not truly capable of measuring slow speed equipment and providing a true mechanical diagnostic analysis. These devices can actually create a reactive maintenance result that the device was supposed to prevent.
For example, a motor shop in South Texas had completed a rebuild of a 100 HP motor. The motor is used in the oil and gas industry. It has an average running speed of 30 RPM. The customer tested the motor on their motor test stand. As it was in its test cycle, vibration was measured using a self-diagnostic vibration analyzer. The results and diagnostics the analyzer provided to the customer was “please replace bearing”. After several further tests running the motor on the test stand, the customer refused to accept those results and retested the motor using a VIBXPERT II analyzer with machine templates designed for slow running machinery and a VIB 6.147 low frequency accelerometer.
The final analysis revealed a high unbalance condition on the motor (11 mils peak-peak). The motor shop followed up with a balancing job (single plane) on the motor. The balancing was performed with the VIBXPERT II as well. Subsequent tests showed that the unacceptable low frequency amplitude that had been observed (11 mils pk-pk) prior to performing the balance job had now disappeared. Final mechanical diagnostics showed no problems and the bearings were in proper condition. A balance report was printed and the motor was ready to leave the shop.
If you want to increase your uptime and availability and reach your financial goals, a proper investment in Condition Monitoring and reliability will provide a positive return on your investment.
by Alex Nino CRL