Up Time Magazine - December 2008/January 2009 - (Page 43) to line frequency, you can reverse calculate the number of rotor bars by highlighting the 2nd of the four peaks and clicking the estimate bars button on the screen. When using this feature to estimate the number of rotor bars you should always include a note with the test stating that the numbers of rotor bars is an estimate only until you can confirm the actual number of bars. the necessary information to make informed maintenance decisions concerning the severity of an air gap eccentricity. With the MCE RIC test and the EMAX eccentricity high frequency spectral analysis test, the MCEMAX provides one easy to operate package for comprehensive evaluation of air gap eccentricity during operation or when the motor is secured. Doug Swinskey joined the PdMA Training & Technical support team in June 2005. Prior to joining PdMA Doug spent over ten years MCEMAX Helpful Hints Rotor Influence Check • Slow motors require testing an additional pole face. When testing a slow speed motor, remember one pole face could equate to positioning the rotor 30 degrees or less. If there is an air gap eccentricity, a RIC, which only covers one pole face, will not have enough of a change mechanically in the rotor/stator relationship to cause the inductance readings to vary much, if at all. • Use the balance of inductance to determine if you should continue the test. The graph of inductance imbalance is produced during the RIC test to aid the operator in determining if a second pole face should be completed. If the balance of inductance changes by 2 or more, a second pole face should be performed. The extra data will facilitate the data interpretation. Eccentricity Test • For VFD powered motors, strobe/tach speed. The added difficulty in determining the speed of a VFD powered motor from the High/Low Resolution or ASA means it is always better to be absolutely sure of motor speed. An external tachometer or strobe should be used to confirm speed and if the number of bars is known, the data analysis becomes automatic. • The X16 scale will fit 4 peaks. When manually searching (scrolling down from the higher frequency of the spectrum) the X16 scale display of the spectrum will give you just enough “window” to see four peaks 120 Hz apart. Keep this in mind and the manual search will become quicker. with a leading manufacturer of electronic motor speed controls. Before he began his work with variable frequency drives, he was the proprietor of an electric motor rewind and pump repair shop. Since joining PdMA Doug has had the opportunity to conduct training on the MCEMAX all over the United States and as far away as the Canary Islands. With all his travel he still finds time to operate a successful photography studio in historic Ybor City in Tampa, Florida. You can reach Doug at 813-621-6463, ext. 2. Summary Eccentricities in the air gap will develop uneven magnetic pull between the stator and rotor during operation. This uneven magnetic pull will lead to increased vibration, mechanical wear and tear, and possibly pull-over to the point of a rotor/stator rub. It is important to have equipment that provides you with www.uptimemagazine.com 43 http://www.filterelement.com http://www.filterelement.com http://www.uptimemagazine.com
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