Are the vibration values correct?

An axis that rotates at 10 RPM (0.16 Hertz) has been monitored with the SKF CMSS 2200 sensor; when looking at the Typical Frequency Response chart it is observed that 0.16 Hertz falls outside the minimum range (0.70 Hertz) of the curve, so my query is: is this transducer not valid for the velocity mode ?, if so, then the values of vibration obtained with this transducer are not correct ?.

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Original Post

– ±3 dB: 0,7 to 10 000 Hz • Resonance frequency, mounted,

jorgeluis-2000 posted:

An axis that rotates at 10 RPM (0.16 Hertz) has been monitored with the SKF CMSS 2200 sensor; when looking at the Typical Frequency Response chart it is observed that 0.16 Hertz falls outside the minimum range (0.70 Hertz) of the curve, so my query is: is this transducer not valid for the velocity mode ?, if so, then the values of vibration obtained with this transducer are not correct ?.

The spec reads ±3 dB: 0,7 to 10 000 Hz.  This means, if we look at a reference quantity of 1 unit, then -3 dB is a level of about 0.71.  +3 dB would be a level of about 1.41.  Fairly substantial errors as you can see but perhaps acceptable if you are trending information.  The errors at your 0.16 Hz (10 cpm) are so far outside acceptability that aren't stated.  Consider the device useless at that frequency.

Next problem "...so my query is: is this transducer not valid for the velocity mode".  The device is an accelerometer so some form of integration is necessary to get velocity.  Integration of low frequency signals like you have is exceedingly diffiult and usually creates integration noise, further making the low frequency signal content useless.

Look at one last thing, the device is usable up to 80 g's peak.  Do a simple calculation of equivalent displacement at 0.16 Hz only use 1 g peak.  The equivalent displacement at the 0.16 Hz, is almost 20,000 mm pk-pk.  As you can see that would be one machine in serious trouble.

Goodnight:

The shaft has two bearings and rotates at 10 RPM (0.16 Hz), the vibration values measured with this transducer were 2 mm/s and 1.5 mm/s in each bearing respectively, then these vibration values are not correct and should therefore be used another sensor to obtain the correct vibration values?

 

This case is related to application of the vibration system which usually requires knowledge of the vibration system and the machine being monitored.

Excellent comments have been already given by the previous replies but I would also add to consider the failure modes of your machine. If the "most important failures" are related to the shaft (1X), this vibration systems is risky to rely on. If the "most important failures" are related to other frequencies, you need to compare these frequencies to the chart in order to decide on the suitability of this vibration system.

I had a case with a huge seawater pump that was not correctly monitored because of pump's running frequency  (6 Hz) was way below the data collector's frequency span (10-1000 Hz). The machine was dancing at 1X while the data collector was sleeping.

Based on the information you provided, I would not use this sensor without receiving a meaningful justification.

Regards- Ali M. Al-Shurafa

Shurafa posted:

This case is related to application of the vibration system which usually requires knowledge of the vibration system and the machine being monitored.

Excellent comments have been already given by the previous replies but I would also add to consider the failure modes of your machine. If the "most important failures" are related to the shaft (1X), this vibration systems is risky to rely on. If the "most important failures" are related to other frequencies, you need to compare these frequencies to the chart in order to decide on the suitability of this vibration system.

I had a case with a huge seawater pump that was not correctly monitored because of pump's running frequency  (6 Hz) was way below the data collector's frequency span (10-1000 Hz). The machine was dancing at 1X while the data collector was sleeping.

Based on the information you provided, I would not use this sensor without receiving a meaningful justification.

Regards- Ali M. Al-Shurafa

Good evening, a consultation:
If the equipment is rotating at 60 RPM and the data collector shows a total vibration of 1.5 g on the screen, then the total real value of the vibration has been attenuated 1 dB according to the accelerometer Curve Typical Frecuency Response (accelerometer SKF_CMSS2200), this means that all the components vibration of the spectrum have been attenuated 1 dB or only the vibrating component of 60 RPM has been attenuated by 1 dB?.
I will appreciate your technical support.
Greetings and successes in this new year 2019.

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