Questions and Answers of Rotating Machinery Reliability

Give three reasons why the ICP accelerometer is the chosen transducer for vibration analysis.
Which industrial transducer does not require a power supply (selfgenerated signal)?
True or False: The resonant natural frequency of a seismic transducer is in its lower useful range.
What are the negative aspects of using a seismic transducer?
What can be used for a velocity output without the negative aspects of a seismic transducer?
What type of signal is the output of a non-ICP accelerometer?
Why is an ICP accelerometer better than a non-ICP accelerometer?
What is the most accepted input power required for an ICP accelerometer?
True or False: The larger the accelerometer crystal, the lower the maximum frequency range.
What are the pros and cons of measuring and trending demodulated spectra?
What does the unit GSE™ represent on a demodulated spectrum? Is it relevant to other vibration parameters?
Where is a proximity probe use essential to identifying a problem?
What does a field technician need to be aware of when disconnecting the BNC connector on a proximeter of a loaded, running machine?
A proximity probe has a useful frequency range related to what operating parameter?
What is the optimal distance a proximity probe should be mounted from the shaft of interest?
What does a technician measure to set a proximity probe into a machine for the most useful range?
A proximity probe, with a sensitivity of 200 mV/mil, yields a reading of 1 volt. What is the shaft displacement at this probe?
What parameter in a vibration spectrum is most important for separating individual fault frequencies?
What are two key measurements a field technician can see at a proximity probe readout?
True or False: The rotor vibration of an electric motor cannot be read without proximity probes.
True or False: Accelerometers must be used instead of proximity probes to see gear mesh frequencies.
Why is it important to know which parameter you are reading on a proximity probe panel meter?
What will happen to the vibration level of a rotating shaft if there is a mass change at one radial location?
What type of mounting for an accelerometer yields the highest frequency range transmissibility?
What conditions must be met for stud mounting an accelerometer?
A pure sine wave has a maximum peak value of 1.2 V. What is the area under the curve?
True or False: The RMS can be calculated for a nonperiodic time waveform.
True or false: RMS stands for relative mean squared.
True or false: Zero to peak and peak readings are the same thing.
True or false: Peak-to-peak readings are used for displacement only.
True or false: The relationship between displacement, velocity, and acceleration is linear.
What is the value of g in English units?
What do digital spectrum analyzers use to prevent the low-frequency ski slope?
What is a beat frequency?
Does a beat frequency increase or decrease as the frequencies get closer to each other?
What is the beat frequency of two motors, side by side, at 3,585 and 3,580 rpm, respectively?
How many times a minute will a technician “feel” this beat rise and subside?
Power plants need extremely accurate speeds on their turbine generators. One customer had two generators running side by side, and the time between maximum beats was 2 hours. Calculate the beat
Give a list of descriptive labels for the bearings of a motor-driven fan.
Because both radial readings on the top of a vertical motor are horizontal, how can you differentiate them?
Why is there only one axial reading on a given machine?
Two sine waves that are out of phase could still have the same two parameters. What are they?
What is the major drawback of analog-frequency analyzers?
What is the minimum frequency analysis rate for a given maximum frequency range of interest?
What is the minimum horsepower for trending to extend the life of the machine if it’s noncritical?
What is the answer if you add the ball pass frequencies of the inner and outer races?
What is the most important vibration parameter for monitoring machinery overall health?
What key parameter in the data collector and/or route setup must be checked to ensure proper collection of data with an accelerometer?
Motor speed and fan speed are both higher in frequency than what on a belt-driven machine? What is the formula for calculating belt frequency?
Time waveform collections should have settings that ensure how many full cycles of 1× running speed?
What is the best analysis path for breaking down a spectrum with a large number of peaks?
What critical piece of information is required to post analyze variablespeed machinery?
Report writing is very time-consuming. What should be added to a trending database to quickly interrogate vibration data yet yield a quality report?
What alarm type can assist in differentiating between a “good” and a “bad” machine where there are multiple machines of similar design and operation (for example, six pumps of similar
What is the most valuable commodity from a trending program that must be communicated to management of a given facility?
What is the most important item that should be trended on an oil-filled gearbox?
What are the wo most important software features that should be implemented for a successful vibration trending program?
True or False. Gathering data is all that is required for a successful trending program.
True or False. It is best to provide a customer with every piece of recorded data for a final report.
True or False. The analyst should provide at least one plot from their instrumentation in the report that substantiates their findings.
True or False. There is no need for trending of bearings. Bearings have a calculatable performance life, known as the L10 life, and the decision to replace them can be automatically timed by a
True or False. A technician should always be accompanied by an electrician from the customer’s site to open and test electrical equipment and never open “live” electrical cabinets.
True or False. Thermography can provide an analysis of the condition of load carrying connections in motors and Motor Control Cabinets.
Bearings that are oil lubricated can be stationary sumps or can be fed by oil pumps. Where should the oil level be in a bearing with a slinger ring?
True or False. A bearing is grease lubricated. Since grease is good for the bearing, more grease is always better.
What is the most important aspect of using Automatic Lubers for grease application to a bearing?
Electrical testing of motors is a very important Predictive Maintenance procedure. However, cutting away the insulating tape inside the motor terminal box for testing and then re-taping the
A PI (Polarization Index) Test of a motor winding is performed and the 10-minute ratio is 3.0. The curve is a perfect parabolic shape. What is the verdict?
True or False. AC HI pot testing of motor winding systems provides the highest stress available for the evaluation of the winding insulation system. It should therefore be performed ONLY on a new
Troubleshooting charts are an excellent tool and should be used in what context?
Corrective measures should be engineered to eliminate the problem but also concentrate on minimizing what?
Vibration spectra can have many frequency peaks. What is key to simplifying the analysis of the number of peaks of interest?
Unbalance is a fundamental cause of vibration in machinery. What frequency of interest identifies the unbalanced condition of a rotor?
A new pump installation is in process. The key fills the entire keyway in the pump shaft. That keyway is 2 inches long. The keyway in the pump coupling is 1 inch long. Does the key need to be cut,
True or False: It’s completely acceptable to balance a fan with cracks and/ or significant dirt buildup.
A trial weight is added to one end of a long rotor. The vibration level decreases on that end but increases on the other end, and the phase stays the same. What caused this result?
How much weight is added to a rotor by using two full ⅛-inchdiameter welding rods to attach a final weight?
True or False: Welding on a fan blade requires the welding grounding clamp to be placed on the fan impeller itself.
Balance of a customer rotor calls for a balance tolerance of G 0.4. What does the G stand for, and what is the significance of the 0.4 level?
True or False: A rotor that has been balanced down to the G specification is considered ready to ship.
A customer has sent a rotor to your shop for balancing. The balance specification calls for “less than 1 mil vibration.” How would you proceed?
True or False: A rotating assembly with multiple parts can achieve an acceptable balance by balancing all the components separately and then putting all of them together.
Balancing a fan on a motor-driven machine has not dropped the overall vibration sufficiently. What is the next step?
Wheels on a passenger train car have a balance tolerance of G 40. Why is this acceptable?
A balance run using a trial weight placed at a 6-inch radius has called for a final weight of 210 g. The final weight is to be welded to the face of the fan at a radius of 18 inches using a ⅛-inch
A fan and shaft are sent to a shop for bearing replacement. The shop balances the fan in a hard bearing machine operating at 450 rpm. The fan is high speed, being directly driven in the field by a
Electric motors generate heat in their rotor. What is the average time for a loaded motor to reach stable temperature?
A new induction motor is put into operation. The initial vibration is acceptable, but after 1 hour of loaded operation, the 1× vibration has increased to an unacceptable level. The motor is
Trial weight runs have been completed, and the final weight calls for approximately 150 g. Using ¼-inch plate steel, what size piece should be cut if a ⅛-inch welding rod is to be used for
A trial weight should generate a force equal to 10% of the rotor weight in order to establish the location and amount of imbalance. The rotor weighs 100 lb and has an operating speed of 3,600 rpm.
A newbie is out in the field getting ready to balance a fan. The vibration level is severe and predominantly 1× running speed in the radial direction. A trial weight is placed on the fan, and there
The same newbie changes the trial and runs the fan for a new reading. The calculations call for the trial weight to be increased from 100 to 400 g. What should the newbie do?
True or False: Phase information is always required to balance a rotor.
True or False: Trial weights can be attached to the outer edge of a fan wheel just using the clamping bolt.
True or False: A rotor that has been installed in the field, experiences a rise in vibration levels and the ends are in phase. Eventually, the vibration levels call for the machine to be taken off
What setting should the technician use to capture the maximum vibration at every speed during a coast-down?
What setting can the technician change in the data collector or while viewing the data in the historical database to ascertain whether the reason for a large vibration peak is the proximity to a
True or False: The only thing that can cause a high vibration at 1× running speed is unbalance.
True or False: Balancing a rotor suspected of running near a resonant frequency calls for care when increasing the size of the trial weight indicated by a balance program.
The case study that involved balancing a gas turbine that could not pass through its first critical frequency called for use of the existing proximity probe outputs input into a digital FFT using

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