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Converting rms, 0-Peak and Peak-Peak Overall Values

The information provided is for help with Commtest Instruments products:



Note: Applies to Ascent®/MAS VB 7.41 and earlier only.

QUESTION

How do I show the overall vibration value in rms, 0-peak or peak-peak?

ANSWER

Versions of Ascent/MAS VB 7.41 and earlier can only display overall values in rms.

Later versions of both the software and firmware (Ascent 8.00 and vb 3.00 upwards) can display overall vibration values in 0-peak and peak-peak (as well as rms). You can upgrade to the latest software and firmware versions by contacting your local reseller.

Alternatively, you can manually convert the rms values to 0-peak or peak-peak using paper, a calculator and the formula given at the end of this article.

When the vbSeries® products were being designed, we made the decision to show overall vibration in rms only. This is because the overall vibration value is calculated by literally using the 'Root Mean Squared' formula. The 0-peak and peak-peak values for overall vibration are artificially generated by using a scaling factor.

What is commonly called an 'overall 0-peak value' is calculated by multiplying the rms value by 1.41421356 (root 2).

What is commonly called an 'overall peak-peak value' is calculated by multiplying the rms value by 2.82842712 (2 times root 2).

The 'true' peak-peak value is calculated by measuring the difference between the highest and lowest peaks in the vibration waveform. There is no simple relationship between this value and the overall rms value for normal vibration waveforms. Very few vibration analyzers use this value for the overall vibration measurement.

If you are using overall 0-peak or overall peak-peak criteria for vibration levels you can convert your criteria levels to overall rms by multiplying by one of these scaling factors:

To convert overall 0-peak values to overall rms multiply by 0.707106781 (1 over root 2).

To convert overall peak-peak values to overall rms multiply by 0.35355339 (1 over 2 root 2).

FAQ ID: 11630 Last Reviewed: 12/02/2002