The list of web-based CMMS companies is too extensive and the feature sets are too varied for this column; however, a comprehensive directory of CMMS vendors is published at www.mt-online.com/selection/cmmguide.html. Check with your CMMS vendor to learn more about its Internet options for hosting, accessing, and supporting your CMMS software.

Whether you are a single user, network user, or an Internet user of CMMS, there are a number of independent Internet resources that can help you increase software productivity.

Maximo-users.net is not connected with the publishers of Maximo software. It was designed originally to assist Maximo users in connecting with each other to provide advice and exchange ideas for productivity. It has grown into a very impressive resource site for any CMMS user. Visit the download area for free failure code templates, RCM analysis codes, PM descriptions, report templates, MTBF tracker, and more.

Sapcenter.com offers support specifically for users of SAP, the giant German enterprise software supplier for many of the world's largest corporations. SAP is one of the most powerful enterprise software systems available, and it is also one of the most reviled because of the software's complexity. Click the SAP CD tab to learn more about SAP training for the Plant Maintenance module. A list of helpful SAP resource links is also part of this specialized site.

Maintenancebenchmarking.com is running an online CMMS benchmarking survey with a goal of collecting data from 1000 CMMS users. It has logged over 250 responses and is growing daily. Survey participants get access to the benchmarking results in real time and in summary form to compare their CMMS productivity to others from around the world.

CMMSCity.com is an independent CMMS site with a wide variety of white papers, book excerpts, and presentations on various aspects of CMMS/EAM. Articles range from practical topics such as "ROI Calculation for CMMS Projects" to IT-related issues such as ".Net and the Future of Enterprise Asset Care."

Perspective CMMS is a British CMMS consultant's site that gives away many of his secrets online at no cost. It also offers a CMMS audit by e-mail.

We hope you find these CMMS resources useful and that you will share useful maintenance sites with us for future columns. Please send your comments, suggestions, and web sites. MT

Reliability Centered Maintenance (RCM) is not new. Airline Maintenance Steering Group (MSG) Logic, the predecessor to RCM, has existed since the early 1960s. F. Stanley Nowlan and Howard Heap of United Airlines introduced formal RCM to the commercial aviation industry in 1978. Airline reliability is primarily based on this work. The vision is as relevant today as it was when the first edition of Reliability Centered Maintenance was published in 1978.

Today, almost everyone in a manufacturing, power generating, or technological environment is familiar with the concept of RCM. However, the perceived degree of familiarity with RCM may be deceiving. RCM is simple in concept but also sophisticatedly subtle in its application.

As with many processes, a simplistic and limited understanding of RCM may prove more problematic than beneficial. The false comfort level of naïvely believing that a superficial implementation of the process will become a panacea for plant equipment problems and then depending on that process to produce significant reliability results is unrealistic.

Analyzing a system
The simple understanding of RCM consists of identifying system functions, functional failures, consequences of those failures, etc. However, Nowlan and Heap gave great importance to understanding hidden failures which are not widely understood and are often overlooked when performing an RCM analysis.

The true reliability benefits of RCM become evident only with a thorough understanding of how to functionally analyze a system. Understanding hidden failure modes, understanding when a single-failure analysis is not acceptable, and understanding when run-to-failure (RTF) is acceptable, are the real cornerstones of RCM. Additionally, the subtle but important distinction between true redundancy and redundant components fulfilling a backup function is also a key to reliability success.

Many utilities and other industries have implemented an RCM program only to find that they continued to have fundamental reliability issues that were not addressed by their analysis. The primary reason is the lack of a grass-roots philosophical understanding of the principles governing the analysis.

Identifying important equipment
Optimizing a preventive maintenance program consists of three phases: Phase 1, identifying equipment that is important to plant safety, operation, and asset protection; Phase 2, specifying the requisite PM tasks for the equipment identified in Phase 1; and Phase 3, properly executing the tasks specified in Phase 2.

At the very least, identifying equipment important to plant safety, operation, and asset protection consists of three programmatic principles that must be well understood before commencing an RCM analysis.

1. Understand the cornerstones for developing an effective RCM program.
2. Identify the defensive strategies for maintaining an effective RCM program.
3. Identify when a component can be classified as RTF and understand the limitations governing RTF components.

A look at each of these principles in detail will illustrate the key areas for successfully achieving plant reliability and maximizing cost containment efforts.

Understand the cornerstones
There are three cornerstones that must be understood for developing an effective RCM program:

• Know when a single-failure analysis is not acceptable.
• Identify hidden failures.
• Know when a multiple-failure analysis is required.

A single-failure analysis is not acceptable when the occurrence of the failure is hidden. When a component is required to perform its function and the occurrence of the failure is not evident to operating personnel, that is, the immediate overall operation of the system remains unaffected in either the normal or demand mode of operation, then the failure mode is defined as hidden.

A multiple-failure analysis is required when the occurrence of a single failure is hidden. Addressing hidden failure modes is a key aspect for maintaining plant reliability.

Identify the defensive strategies
There are three distinct lines of defense for maintaining an effective RCM program. The first strategy for defending a plant against unplanned equipment failures is identifying critical components. These are components where a single failure will result in one or more consequences similar to the following:

• A direct impact to personnel or plant safety.
• A plant trip or shutdown of a manufacturing facility.
• A power reduction, down power, or the loss of a facility’s operational capability.
• An inadvertent actuation of a safety system.
• An unplanned forced outage.
• Other (depending on specific type of plant or industry)

The second line of defense for protecting a plant or facility is to identify what this author refers to as potentially critical components. These are components which, if they fail when called upon to function, the failure is hidden and will not have an immediate effect on the plant. However, the hidden failure in combination with one or more additional failures will result in consequences similar to the following:

• A direct impact to personnel or plant safety.
• A plant trip or shutdown of a manufacturing facility.
• A power reduction, down power, or the loss of a facility’s operational capability.
• An inadvertent actuation of a safety system.
• An unplanned forced outage.
• Other (depending on specific type of plant or industry)

Note the similarities between critical and potentially critical components. The only difference is that critical failures manifest themselves immediately while failures of potentially critical components are hidden and will not manifest themselves until a second, multiple failure occurs.

To better understand the concept of potentially critical components (which is totally different from the potential failure of a given component) consider the following example.

When two or more components (valves, pumps, motors, etc.) operate in parallel flow paths to supply a function but only one component is required to fulfill the function, and there is no indication of failure for each component individually, then a failure of one of the components will be hidden (there will be no indication the component has failed) and the failure will not result in a plant effect. However, if the second component should fail, then a plant-effecting consequence would occur. Hence, the component is considered to be potentially critical.

Another example involves a pump discharge check valve. If there are two pumps operating at the same time, a failure of the check valve in the open position will be hidden. Only when one pump fails will the unwanted reverse flow path through the failed open check valve become evident.

How prevalent are hidden failures? Extremely. Just a few examples include main turbine overspeed components, many check valves, diesel generator fuel oil pumps, and emergency diesel generator shutdown components. Identifying potentially critical components affords perhaps the greatest degree of reliability protection for a plant or facility.

Hidden failures are typically failures of one or more components aligned in parallel with no indication of failure for each individual component. In Fig. 1 for example, one of the two components could fail but since each one by itself can satisfy the function, only when the second one fails will the functional failure become evident; therefore, the failure of the first component is potentially critical.

How important is this concept? Very. There are many examples in industry where a designer intentionally builds in multiple redundancy to ensure reliable system operation. Unfortunately, if the redundancy has no way of manifesting itself when it fails, a plant-effecting consequence can occur with the second failure.

There is a vast difference between a component operating in a backup function and one that is not (Fig. 2). In Example 2, the component is an RTF component while the component in Example 4 is critical.

The third line of defense to protect a plant is to identify economically significant components. These are components whose failure will not be critical or potentially critical, but will result in one or more of these economic concerns:

• An unacceptable cost of replacement or restoration.
• An unacceptable corrective maintenance history.
• A long lead time for replacement parts.
• An obsolescence issue.
• Other (depending on specific type of plant or industry)

Failures of economic components have no effect on plant safety or operability. Economic failures will result only in labor and/or parts replacement costs. It is important to keep this economic categorization separate from critical and potentially critical components to enable a prioritization of work.

Note: If a failure occurs to a major piece of equipment (even if it is economically significant) but it results in an effect on plant safety, operation, or a plant outage, it would be more than merely an economic consideration. It would be captured as either a critical or potentially critical consequence of failure.

Identify RTF components, understand limitations
RTF in its most basic definition means PMs are not required prior to failure. This does not imply that the component is unimportant and never needs to be fixed. Corrective maintenance is required in a timely manner after failure to restore the component to an operable status. RTF components are understood to have no safety, operational, commitment, or economic consequences as the result of a single failure. Also, the occurrence of failure must be evident to operations personnel.

RTF components are designated as such because a failure is evident and there is no significant consequence from a single failure. If it does not matter whether a failed component is ever restored to an operable status, one would question why that component is even installed in the plant.

The heart of reliability is a sound preventive maintenance program and RCM provides the most prudent approach for establishing an effective PM program. MT

Neil Bloom is program manager, RCM and preventive maintenance programs, at Southern California Edison’s San Onofre Nuclear Generating Station. He previously worked in the commercial airline industry in both maintenance and engineering management positions. He can be reached at Mail Unit K-50, P.O. Box 128, San Clemente, CA 92672; (949) 368-6378

From the very start, the implementation of a computerized maintenance management system (CMMS) is a long and arduous process. One of the largest concerns is how to effectively get the correct data into the system in the first place, and then, how to get useful information out.

What follows can provide a method to get better data into the CMMS with every work repair request. The yield is more and better data for analysis, which is the all important question in the long-term successful evaluation of the implementation—is this information tool providing useful information?

There is no replacement for a good, integrated implementation plan that covers the setup of the database, training, data design and collection, etc. Consider this as an enhancement to be added to the existing plan.

Repair data
Basic repair data fields come in four categories:

• Origination
• Planning
• Scheduling
• Results

Origination data includes the emergency flag, the original observer of the problem and how the person can be reached, the equipment experiencing the problem, and a problem description. This data must be obtained to effectively get labor and materials assigned to the job.

Although it is most important to get all data consistently and correctly into each field, most problems occur at work order origination and multiply as the work order is processed. See accompanying section "Work Order Data Fields."

The two most important fields at the origination of a repair are the equipment number and the problem description. The equipment number is needed to get the person to the correct equipment, as well as to insure charges are posted back to that piece of equipment for historical detail as well as summary analysis of its department, process, unit, etc.

The importance of the problem description cannot be understated. Whenever a CMMS is implemented, every person who may originate a work order should be trained to call in (type in, write in, etc.) the problem description. This should include what was observed that prompted the call. Sample bad problem descriptions:

• "It’s not working" or "It’s down."
• "It’s broken."
• "It sounds like it is going to fail."

Bad problem descriptions do not provide enough descriptive data and they lead to bad descriptive results such as:

• "It’s working" or "It’s up."
• "It’s fixed."
• "Sounds OK to me, just a little noisier than normal."

If the historical records within the system contain descriptions similar to these, plan to retrain everyone immediately and include a sample of these records to show how useful (or not) they are for historical analysis.

More effective descriptions would be based on what the observer/originator of the problem sensed:

• Saw a leak
• Heard excessive gear grinding or a pop in the disconnect panel
• Smelled something unusual burning
• Felt excessive vibration at normal run speed
• Tasted like there was too much syrup, but the controls indicate the proper mix

These are oversimplified examples, but a trained mechanic can identify a starting point and promote a response that is more descriptive of the cause. For historical purposes, this can be invaluable in looking at repetitive problems and working toward engineering them out of existence.

Using a basic repair order
Better understanding of why proper problem descriptions should be used is probably the biggest and most inexpensive way to make a major leap in repair data capture.

A basic repair work order has room for free form text, but also specific codes that can be selected to help sanitize what is reported about the work, specifically to enhance analysis, expedite reporting, and, at the same time, not overburden the mechanic with paperwork.

Results data should at a minimum include the skill/trade that completed the work, work time, a work description (what was done), materials used and/or costs, a cause code, downtime, and an assessment of the repair.

The skill should have an associated wage (or wage plus burden) rate so that hours may be converted to costs for charging back to each piece of equipment, and the associated grouping codes (department, unit, etc.), when combined with the work time. The work description should explain the action taken on what part of the equipment.

If recording downtime, it must be defined and all personnel must be familiar with how it is charged and used. The most common discrepancy comes when a machine is out of service for a maintenance reason during a nonoperating shift for that piece of equipment. Is it down?

Get materials costs
Materials used and their costs are helpful for keeping inventory up to date and charging materials to each piece of equipment.

Having the material identified by its tracking number in the inventory control system (whether or not this is a module in the CMMS) is essential for documenting proper part usage and tracking and bill of material building. This is one of the first areas of potential interface when the nonproduct material is maintained by an organization/system outside of maintenance.

This type of interface would allow documentation of the part number, and then the cost could be brought over from the parts inventory control system if it is not in the CMMS.

This cost is especially important in light of the fact that many materials costs can exceed labor costs significantly, and both are necessary to properly assess the maintenance requirements and history of a given piece of equipment.

Assess the repair, use codes
Although additional comments about a job may not be entered, it is a good idea to get the mechanic’s assessment of the repair at least to the point where the repair is identified as "temporary" or not. A temporary repair is most often done to get the operation through the shift, and subsequently a relatively permanent repair is completed at a more convenient time.

For each repair, an assessment should be provided by the mechanic. This comment may indicate the repair was temporary, and if so, it should be followed by a recommendation indicating what needs to be done to make it more permanent.

Last, and not least, is some type of repair cause code. The reason a code is used instead of a description is to begin to categorize the repairs for easier analysis. Once statistical analysis is completed, the more significant individual items can be further analyzed by review and evaluation of their details.

Codes in the CMMS represent a great potential advantage for accelerating recording of repairs, as well as their analysis, but can be extremely dangerous if overused. There should not be so many code fields, and/or codes per field, that it requires a separate page to list the possibilities, and someone must read through them for each repair.

For example, a CMMS may contain fields for problem, failure, cause, root cause, solution, or action verb/noun combinations, etc. For each field, there may be 40 or 50 possibilities, and probably more. This just makes it take longer to complete the work order and often leads to more specific codes being added, thus making the recording process even more complicated.

An important aspect to documenting work is simplifying the process. Use codes that are broad in nature, and relevant to the process environment wherever possible. An invaluable source of these codes is a review of historical activities that probably exist on manual records. Causes can be derived from work descriptions entered even if they are only to categorize parts problems from electrical, leaks, adjustments, etc.

Multi-line work order
The basic work order example is considered the workhorse for capturing planned and unplanned work, and provides areas to document extensions when the work is carried over for virtually any reason (scheduling, availability of materials, etc.).

A multi-line work order that mechanics would have at the beginning of their shift is typically used to capture work that is often unplanned and would be completed during the shift. Items carried over are typically referenced from here and transferred to the basic work order form for future execution.

The better and more consistently recording of repair activities is done, the greater potential for yielding greater and more specific information about the operation, in both qualitative and quantitative terms. The more quickly this can be done, the sooner actual activities will be reported into the CMMS, and a useful history will be built that can be more easily analyzed through statistical methods. MT

Christopher N. Winston is an independent professional in the Detroit, MI, area contracted to HSB Reliability Systems Group, 1701 N. Beauregard St., Alexandria, VA 22311. He has more than 18 years’ CMMS implementation and business system analysis experience and has a bachelor of science degree in mechanical engineering.

Machine conditions change from the time the machine is off line to when it is running under normal operating conditions. Some of these changes are due to process forces (e.g., fluid pressures, airflow, etc.). The most notable of these changes is the change in the temperature of the machine bearings and supports. This is called the machine's thermal growth.

Thermal growth is the change in the length of a particular metal as a result of the change in temperature of that metal. Typically, when a metal bar is heated, it will get longer. These changes can be very small (0.0005 in.) or they can be very large, depending on the length of the piece of metal and its coefficient of linear expansion.

Formula for thermal growth

The formula used for this calculation is often referred to as the T x L x C formula. T represents the change in the material's temperature in degrees Fahrenheit, L represents the length in inches of the material, and C represents the material's coefficient of linear expansion. Different materials have different C values. Using the formula, we can anticipate the change in a machine's shaft alignment based on the expected changes in machine temperature. Fig. 1 is a chart of the most common machine materials and their C values.

Consider the following example: A motor with a starting temperature of 70 F is perfectly aligned to the pump shaft it will be driving. For this exercise, the temperature of the pump will not change; however, the temperature of the motor will increase to 120 F under normal operating conditions. The motor end bell's material is cast iron with a C value of 0.0000059. The distance from the bottom of the motor feet to the center of the shaft is 15 in. We now can calculate the change in position of the motor from off line to running by multiplying the T, L, and C values. T x L x C = growth (120 F  70 F) x 15 in. x 0.0000059 = 0.0044 in.

Based on this information, the motor will grow 0.0044 in. or 4.4 mils. If the growth of the motor is the same for both ends, the result will be a change in the offset alignment of 4.4 mils but the angular alignment will not change. This motor shaft should be aligned 4.4 mils lower than the pump shaft which will allow the machine to grow into an aligned condition.

Temperature changes unequally
That was a fairly simple example and does not accurately reflect what will happen to an actual machine. In reality, the temperatures of all the machine supports will change; however, they will almost never change equally.

Using the above machine example, consider the change in shaft alignment if the outboard end (OE) bearing temperature changed by 20 F and the drive end (DE) bearing temperature changed by 50 F. The drive end bearing would grow by 4.4 mils; however, the outboard bearing would grow only by 1.8 mils. The result will be a change in both the offset and angular alignment. If the motor feet are 20 in. apart, the change in the angular alignment will be 0.13 mil/in. [(4.4  1.8)/20 = 0.13] open at the top of the coupling. Changes in the temperature of machines from off line to running can have a significant impact on the shaft alignment.

These changes in the shaft alignment can be accommodated in a few different ways. One way is to align the machines to zero and then remove or add the amount of shim under the machine feet as determined by the temperature data. Another way is to gather the alignment data, graph the results, and predetermine the actual shim corrections based on the graph.

With today's modern laser alignment technology, accounting for thermal changes at the machine feet is actually a simple evolution. Most alignment systems on the market today have within them a function that allows the user to program the foot targets of the machine being aligned. For the previous example, the front foot target would be -4.4 mils and the back foot target would be -1.8 mils. After programming the determined foot target values at the machine feet, the user aligns the machines to zero on the display unit. The shaft alignment system will automatically calculate the required foot corrections to leave the feet at the prescribed positions. As the machine heats up, the shaft centerlines will grow into a properly aligned condition.

Gearboxes are difficult
Thermal changes in gearboxes can be especially difficult to calculate. Often the input shaft temperatures will be different from the output shaft temperatures. This causes the gearbox shaft alignments to change in the horizontal plane as well as the vertical plane.

Force-lubricated systems with an oil cooler also can have an effect on the final alignment condition of a machine. Higher oil temperatures out of the cooler will result in a hotter operating condition of the machine, therefore creating a more drastic change in the running alignment condition. A 10 F change in the operating temperature of a turbine from 105 F to 115 F can change the foot positions as much as 2-4 mils. The alignment condition of turbines and compressors that operate at very high speeds can be adversely affected by these relatively small temperature changes.

Pipe strain
Another condition that changes is the increase or decrease in temperatures of the suction and discharge piping attached to pumps and compressors. Some compressors may actually form ice on the suction end while the discharge piping is too hot to touch. Conditions such as these can force major changes in the operational alignment condition of machines.

While original equipment manufacturers might be able to anticipate the nominal changes in operating temperatures of a piece of equipment, they cannot accurately anticipate the effects of the piping configurations of the final machine installation or the changes in the temperature of the piping runs. Piping runs are typically very long and can have a tremendous impact on the change in the shaft alignment from off line to running condition. In addition, piping connections act as fixed (or restraining) points with respect to the tendency of machines to move/grow when on line. The effect of these fixed points on the final position of the machines is almost impossible to calculate or predict.

Depending on the piping configuration, these changes may be in the vertical plane or in the horizontal plane and are extremely difficult or impossible to accurately calculate based on the TLC formula above.

Consider two identical boiler feed pumps (BFP) as shown in Fig. 2. BFP #1 feeds boiler #1 which is 20 ft away and BFP #2 feeds boiler #2 which is 60 ft away. The length of the discharge piping on BFP #2 will be approximately three times longer than that on BFP #1. This will result in the two "identical" machines showing drastically different alignment changes from off line to running. A great deal of care must be taken when calculating the changes in the alignment condition of these machines. Just because two machines appear identical and serve the same function does not ensure they will exhibit the same operational characteristics.

Determining alignment changes
In the past, there have been several methods used to attempt to measure the changes in the shaft alignment of two or more machines. One of these methods involves measuring the changes in machine temperatures at each machine support and performing the target alignment based on mathematical calculations.

Another method relies on tooling balls mounted on machine bearings. Typically an optical transit (scope) is used to measure the off line positions of the tooling balls. Once the machine is at operating conditions, another set of measurements is made; the positional changes are compared to the "stationary" tooling balls. These changes are triangulated to calculate the change in the position of the shafts.

There is a variant to the above technique, the Acculign method, which involves installing tooling balls in the foundation as well as at the bearings. The distance between the fixed tooling balls (mounted in the foundation) and the bearing-mounted tooling balls is measured off line and then on line. Precise measurements of the distances and angles are required to make the calculations of the growth.

Doing hot alignment checks
Another way to gather this data is to perform a hot alignment check of the affected piece of equipment. The procedure for this is relatively simple. The machine is aligned off line and the results of the alignment are documented (horizontal angularity, horizontal offset, vertical angularity, and vertical offset). The machine then is placed on line and allowed to reach normal operating conditions. At this point, the machine is shut down and allowed to stop rotating.

The alignment system is remounted on the machine and the shaft alignment is remeasured and documented. Now the machine may be aligned hot by reshimming and repositioning the moveable machine as quickly as possible. One drawback of this method is that the machine will begin to cool as soon as it is shut down, adversely affecting the accuracy of the hot alignment check.

If the two sets of alignment readings were documented, a set of cold alignment targets can be calculated. Alignment results (hot)  alignment results (cold) represents the change in the alignment condition of the machine from cold to hot. The alignment targets for this machine will be the opposite of the changes in the alignment parameters.

While this is currently a widely used method of hot-aligning machines, it will measure only the changes in the shaft alignment due solely to the changes in the machine's temperatures. Discharge pressure, shaft torque, multiple machines operating in parallel, electrical loading of a generator, etc., also can play a large role in the change in the alignment condition from off line to running. These changes most often will be seen in the horizontal plane, but could affect the vertical alignment as well.

Yet another factor to consider is the location of the machine. If a machine is located indoors in a controlled environment, the operating characteristics should be relatively constant throughout the year. A machine that operates outdoors and is exposed to large changes in temperature also could exhibit extreme changes in its shaft alignment as the temperature changes (as in the change of seasons).

On line positional change measurements
One method used to measure the change in the alignment of two pieces of machinery is to document their bearing cap positions in both the horizontal and vertical planes relative to some fixed points in space while the unit is off line. After the data has been documented, the machine is started and placed on line. When the machine has reached its normal operating temperature, the positions of the bearing caps are measured again and compared to the points that are stationary. The movement of the machines and the changes in the shaft alignment then can be either calculated or graphed.

In the past, there have been problems obtaining on line readings using this method. A nominal amount of vibration can make an optical scale very hard to read through a transit or theodolite. Care must be taken that the scale is placed back in the exact location for each measurement at each point. Bearing caps are not typically precision machined on the outside surfaces. A very small deviation in the position of the detector can lead to a very large error if the surface that is being measured is not flat and smooth.

Modern laser-based measurement systems designed to measure flatness and surface parallel also can be used in this manner. One benefit of the laser-based positional measurement systems is that the data can be averaged, eliminating the potentially large errors when measuring machines that are running. When the laser beam strikes a vibrating detector surface the data will appear to bounce slightly. A simple function in the display unit will sample the data for the desired amount of time, locate the maximum and minimum values on the detector, and average the data accordingly. Since vibration, by definition, is cyclic and repeatable, very good results can be obtained.

Laser measurement systems
In the 1980s, a laser-based system became available that mounted to the drive end bearings of a machine to monitor the changes in the machine's alignment from cold to hot or from hot to cold. Two laser transmitter/detectors are mounted on the stationary machine drive end bearing. One of these transmitter/detectors must be positioned in the 12 o'clock position (to monitor vertical changes) and the other must be positioned in the 3 o'clock position (to monitor horizontal changes). The transmitter/detectors are positioned coaxially with the stationary shaft centerline and level. Corresponding prisms are mounted on the moveable machine drive end bearing. They are positioned to reflect the laser beam back to the detectors mounted on the stationary machine.

The transmitter/detectors are hooked up to a computer running the measurement software. The user now can program the alignment monitoring equations into the software and have the system monitor all four alignment parameters simultaneously. The values are auto-zeroed and the data collection begins. When the machine is started and the alignment changes, it is recorded in the system software. When the machine reaches normal operation, the data collection is stopped and the alignment changes calculated. The results are displayed as a graphical trend.

The cold alignment targets will be opposite of the measured change in the machine alignment if the data collection was started when the machine was cold. If the cool down was monitored, the targets are equal to the values displayed in the software. While this system can be very effective for diagnosing alignment problems, it also can be very time consuming and frustrating to set up and monitor. Any change in the bracket position during the data collection will introduce errors into the results. This system also requires the user to purchase a PC to use for the data collection. MT

Contributors to this article include Rich Henry, Ron Sullivan, John Walden, and Dave Zdrojewski, all of VibrAlign, Inc., 530G Southlake Blvd., Richmond, VA 23236; (804) 379-2250; e-mail info@vibralign.com

COMMON MATERIALS AND THEIR C VALUES

Fig. 1. Different materials have different C values (coefficient of linear expansion).

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