Good morning, please provide your support regarding the following query:
How Much is Too Much at Specific Vibration Frequencies for Various Machine Types?
- At Operating Speed (1x RPM)
- At 2x RPM
- At 3x RPM
- At 2x Line Frequency in an Induction Motor
- At 1x and 2x Rotor Bar Pass Frequency in an Induction Motor
- At Blade Pass Frequency and Harmonics
- At Gear Mesh Frequency and Harmonics
- At Belt Frequencies and Harmonics
- At Rolling Element Bearing Frequencies and Harmonics
Greetings and success.
A useful reference is Narrowband Spectral Alarm Envelopes by Technical Associates of Charlotte.
Vibration limits for the frequencies you list vary. In general, the limits in the ISO 10816-x series of standards would apply, depending on the type of machine, to the extent that they contribute to the overall vibration amplitude. (ISO 10816-3 only provides limits for overall amplitude, not for individual frequencies.) (See the list below). An important exception is vibration at "Rolling Element Bearing Frequencies and Harmonics". If peaks in a spectrum are identified as originating from a rolling bearing, the bearing has already developed a fault and is in a failure stage, regardless of the amplitude of the peaks. There is more to the analysis of rolling bearing faults in the spectrum than can be covered in an email, but a single peak in the spectrum that matches with a calculated bearing fault frequency is very likely not originating from a rolling bearing fault; there will almost always be peaks at the fault frequency harmonics and often sidebands of 1xRPM and FTF frequencies.
In addition to the ISO 10816 standard, there are vibration limits provided for electric motors in the EASA AR100 standard for electric motors. These limits are reflective of the those in the NEMA MG1-Part 7 standard for new motors being tested no load on a resilient base, (durometer pads). Vibration at 2x line frequency (2xlf) on induction motors is given special treatment in that NEMA standard. When there is a beat frequency present between vibration at 2xRPM and 2xlf, the rms average of the beat amplitude is applied to the limit. Again, these NEMA and EASA AR100 limits apply only to motors tested no load on a resilient base and not to motors connected to a load in situ.
For vibration peaks in the spectrum that are identified as rotor bar pass frequencies, the limits in ISO 10816-3 are applicable, to the extent that they contribute to the overall vibration amplitude. (ISO 10816-3 only provides limits for overall amplitude, not for individual frequencies.) Vibration at rotor bar pass frequencies are always present on induction motors, usually at very low amplitude. Only when these peaks increase over time, (weeks, months), are they an indication of a possible rotor cage fault. Vibration is not a good indicator of rotor cage faults and any suspected fault should be confirmed with other tests such as a motor current signature analysis.
The Hydraulic Institute provides overall vibration limits for various types of pumps that could be an alternate to the limits in ISO 10816-3, that would cover blade pass frequency on pumps.
Blade pass frequencies on fans, blowers and similar machines would be covered by ISO 10816-3, as would vibration at belt frequencies and gear mesh frequencies.
I hope that is helpful.
Gene Vogel, EASA Pump & Vibration Specialist
Here is a list of the currently published ISO 10816-x standards:
ISO 20816-1:2016 - Mechanical Vibration - Measurement And Evaluation Of Machine Vibration - Part 1: General Guidelines
ISO 20816-2:2017 - Mechanical Vibration - Measurement And Evaluation Of Machine Vibration - Part 2: Land-Based Gas Turbines, Steam Turbines And Generators In Excess Of 40 MW, With Fluid-Film Bearings And Rated Speeds Of 1 500 R/Min, 1 800 R/Min, 3 000 R/Min And 3 600 R/Min
ISO 20816-3:2022 Mechanical vibration - Measurement and evaluation of machine vibration - Part 3: Industrial machinery with a power rating above 15 kW and operating speeds between 120 r/min and 30 000 r/min
ISO 20816-4:2018 - Mechanical vibration - Measurement and evaluation of machine vibration - Part 4: Gas turbines in excess of 3 MW, with fluid-film bearings.
ISO 20816-5:2018 - Mechanical vibration - Measurement and evaluation of machine vibration - Part 5: Machine sets in hydraulic power generating and pump-storage plants
ISO 10816-6 - MECHANICAL VIBRATION - EVALUATION OF MACHINE VIBRATION BY MEASUREMENTS ON NON-ROTATING PARTS - PART 6: RECIPROCATING MACHINES WITH POWER RATINGS ABOVE 100 KW
ISO 10816-7:2009 - Mechanical vibration - Evaluation of machine vibration by measurements on non-rotating parts - Part 7: Rotodynamic pumps for industrial applications, including measurements on rotating shafts
ISO 10816-8:2014(en) - Mechanical vibration - Evaluation of machine vibration by measurements on non-rotating parts - Part 8: Reciprocating compressor systems
ISO/DIS 20816-9(en) - Mechanical vibration - Measurement and evaluation of machine vibration - Part 9: Gear units
ISO/AWI 20816-10 - Mechanical vibration - Measurement and evaluation of machine vibration - Part 10: Turbomachinery
At 1x and 2x Rotor Bar Pass Frequency in an Induction Motor
It is often necessary to look at up to 4- 6 RPM frequencies here, because the side frequencies are not visible in the first two or three RPM harmonics .
Problems with the rotor cage will often be seen like one big peak in the early stage at 1 or 2 x the number rotor bars x RPM frequency with two side peaks at 100Hz .
That is why it is a good recommendation to count bars at the rotor cage when overhauling electric motor
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