Predictive Maintenance Technology Conference
September 19-22, 2005
Atlanta, Georgia

• Improving Motor Reliability with Advanced Instrumentation
• Identifying Motor Defects Through the Six Fault Zones
• AC Motor Testing
• Developing a Motor Management Program
• Multiple Discriminant Analysis
• Alignment 101
• The Shock Pulse Method For Condition Monitoring
• Motor Electrical Predictive Maintenance & Testing Workshop

+ 30 other condition monitoring short courses, workshops and learning zone sessions

+ Every PdM-2005 attendee has a chance to win an Alienware Laptop

Bring 3 PdM Team Members and get the 4th free - a 25% discount

To register for PdM-2005 please call 888-575-1245 or…

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Bias Output Voltage Indicates Accelerometer Faults

Most accelerometer faults can be diagnosed by measuring the Bias Output Voltage (BOV) of the sensor amplifier. If the BOV is within correct limits, the sensor is most likely operating properly. Most cabling faults can also be isolated by measuring the BOV.

The BOV is normally 12VDC, although this may vary depending on sensor manufacturer and design. The specification sheet for the accelerometer will provide information on the BOV for each model of accelerometer. The BOV is determined by the amplifier design and is not adjustable. The BOV will remain the same regardless of the input power to the accelerometer, as long as the input power is within the specified range. Most two-wire sensors produce an 8-14 Volt bias. The BOV should be measured periodically to check sensor operation.

Open Bias Fault (18-30 Volts)
When the measured BOV equals the supply voltage, the sensor amplifier is disconnected or reverse powered. In most cases, the problem is in the connector or cabling.

Short Bias Fault (Near 0 Volts)
When the BOV measures zero Volts, power failure or a system short is usually the problem. If the power supply is on, there is usually a short in the cabling.

Low Bias or High Bias Fault
Out of specification BOV readings other than those above usually indicate sensor damage. Common sources of sensors damage are exposure to excessive temperature, excessive shock, mis-powering, and electrostatic discharge.

Erratic Bias
The BOV should remain stable and unchanging. Shifting BOV indicates a very low frequency signal that is not filtered out by the bias meter. In rare cases, this indicates an actual low frequency signal, however in most cases this indicates a fault. Primary causes of erratic BOV are thermal transients, poor connections, ground loops, and signal overload. Each of these faults will also be visible in the time waveform as an erratic jumping or spiking of the signal.

For more information on Bias Output Voltage, read Wilcoxon’s Technical Note 14: “Troubleshooting Industrial Accelerometer Installations.” This Tech Note from Wilcoxon’s extensive online Knowledge Desk explains BOV, gives examples of sensor readings and the faults they indicate, and includes a Trouble shooting chart for sensors.

Wilcoxon’s Technical Note 14: “Troubleshooting Industrial Accelerometer Installations.”

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Maintenance Planning and Effective Communication

Successful organizations are built around effective communications between all functions within the organization. When we ask the question “How effective are we in our communications”? In most cases the answer is poor. The first place to start making improvement is between the maintenance planner and the first line supervisor. In most cases, these individuals are not, will not or do not see a need to communicate. This combination has to become a synchronized team that anticipates each other’s needs. To accomplish this relationship daily dialog is essential. This dialog has to center on improving and/or maintaining the reliability of the equipment or process. Morning and afternoon communications have to take place which typically focus on current work progress, work request scope clarification, labor availability and scheduling issues. Development of this close relationship requires commitment from both parties. The success of this relationship results in everyone being aware of the true maintenance issues and their impact on the overall reliability of the equipment or processes. Once this first step of effective communication is in place and ingrained into the daily routine, the exchange of information will carry over to the maintenance personnel. Reliable equipment and processes are dependent on effective communications between operations and maintenance as well. Everyone contributes to effective communications.

Tip provided by Life Cycle Engineering
http://www.lce.com
Tel: 843.744.7110 x267

Best Practice Maintenance Planning

Check Tank Levels Using Your Infrared Camera

The storage of liquid and bulk materials in tanks and silos is common at many industrial sites. While likely instrumented with sophisticated tank level monitoring equipment, many storage tank levels can be quickly determined under the right conditions using your infrared camera.

The volume in a tank is filled with a material and any remaining headspace. During the day the tank and its contents absorbs the sun’s energy. Obviously the mass of the material and the headspace are very different. Since thermal cameras are very sensitive (usually to less than 0.1°C) it is easy to take advantage of the daily changes in a tanks volume temperature. Earlier in the day the headspace will heat up faster than the stored material, resulting in an image that shows the empty volume as warmer than the filled volume. After sunset the headspace will cool more quickly than the filled volume causing the filled space to be warmer than the headspace. Sometime during this period an event called thermal crossover will take place when the two volumes are at the same temperature. Because this is a transition state the duration of near equilibrium conditions is determined by many factors but should last less than one hour.

This technique works best on painted tanks that are not too reflective. If viewing highly reflective vessels it is recommended to view these at early evening when the influence of ambient scene reflection is minimized.

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When analyzing phase data to check for force unbalance, the horizontal inboard and outboard readings will most likely be very similar to the vertical inboard and outboard readings. But if couple unbalance is the culprit, the horizontal readings on the inboard and outboard readings will be approximately 180 degrees out of phase.

Tip provided by LUDECA, INC.
ALIGNMENT * VIBRATION * BALANCING
http://www.ludeca.com
Tel: 305-591-8935

IQ Quiz Vibration Basics Part 2

The 10% Rule of Preventive Maintenance

Many organizations use the metric “PM Compliance” as a measurement of their maintenance department’s performance. This metric is seen many times by professionals as a joke because if your PM Compliance is high but you continue to have many reliability issues then the metric has no meaning. I have seen organizations that report 100% PM Compliance but have over 10% downtime due to reliability issues. Of course many different issues could contribute to this problem.

I wanted to focus on a solution to the PM Compliance Metric in order to make it believable and truly help you feel confident that this metric is a true measurement of compliance to your PM Program. I have tested and proven that if you were to manage your PM Program as a “Controlled Experiment” then you would be able to control reliability with more reliable accuracy.

Now in order to have “Controlled Experiment” we must control the variables such as time. Most PM’s are time based and thus controlling the variance in your PM schedule would allow you to control reliability better and help you make better decisions.

I believe in the 10% Rule of Preventive Maintenance and it simply states:

“that a time based PM must be accomplished in 10% of the time frequency or it is out of compliance”

That statement is a tough one to follow. If you were to apply the 10% Rule to all of your time based PMs immediately, your PM compliance might be less than 5%. Let’s look at this example before we go any further:

Let’s say you have a monthly PM that must be accomplished. Would you agree that:

• If you postpone a PM until the end of the month would you say you completed the PM on time?(yes)
• Next month you complete the same PM at the beginning of the month. Would you say you completed the PM ontime? (yes)
• Next month you complete the same PM task at the end of the month. Would say you completed the PM? (Yes)
• Now what, is the affect of performing time based PM this way? Is this really a monthly PM or an out of control PM? ( I say the PM schedule is out of control and probably so is the reliability of your equipment)

My recommendation is to focus the 10% Rule on time based PMs you are performing on your critical assets first. These critical assets are the ones that will get you in trouble if their reliability is low. I would measure their PM compliance separately from the rest of the equipment. I would also measure equipment capacity on this equipment in order to see the affect of the 10% Rule.

One company I know went from 100% PM Compliance to 50% over night because they decided to measure PM Compliance using the 10% rule on all assets, but equipment uptime went from 89% to 94% as a result of following this process in as little as 3 months. We have been taught by everyone that 100% is the best but I say the “number is the number” whatever it may be as long as capacity or uptime continues to rise.

Tip provided by Ricky Smith, CMRP

http://www.maxzor.com

Click here to view an I-Presentation on this topic