data is collected as an "RMS" value ("Root Mean Square"). That is an ISO
convention and applies no matter what manufacturer's collector you may
value is calculated by simply multiplying the peak amplitude (shown in
the graphic below) by 0.707:
Peak x 0.707
But some analysts
prefer to display the amplitudes as a 'peak' amplitude (usually because
the vibration severity charts they are using are in peak amplitude values).
So how is that value calculated ?
|But is that
the RMS value of a pure sinusoid is equal to the area under
to (peak x 0.707) on a pure sinusoid.
are rarely encountered in the world of mechanical vibration.
Due to that, the
trend amplitude value is calculated by simply multiplying the peak amplitude
In some cases
- specifically the use of displacement amplitudes where the analyst wants
the total amount of bearing movement back and forth - the
'Peak to Peak' value is desired by the analyst. In that case, the peak
value is simply multiplied by 2. Velocity and acceleration units are not
typically displayed as peak to peak since the important piece of information
is what the maximum (peak) value is.
To calculate the
'Peak' amplitude, we divide the RMS value by 0.707.
For those of you
paying close attention, you may have noticed that, from start to finish,
the way a peak amplitude is calculated is:
Measure the peak
Multiply by 0.707
to obtain the RMS value.
Divide by 0.707
to obtain the Peak value.
|So let's summarize:
The highest (peak)
value of collected data is multiplied by 0.707 to obtain the ISO standard
of RMS amplitude. The majority of programs world-wide use this value.
For those programs
that wish to display the data as a 'peak' value, the RMS value is then
by 0.707 to obtain the peak amplitude.
For those situations
where peak to peak amplitudes are desired, the peak amplitude is simply
multiplied by 2.
It doesn't matter which value you use - RMS or Peak - so long as you are
(another very important convention) !! Amplitude is, after all,
simply a number from which we make certain generalizations about the machine
condition. There is no exact, precise number above which disaster awaits
and below which you are safe.
|Be aware of
the conversion if comparing values between programs that use RMS and Peak
values. This applies to spectrum plots as well.
look at the vibration sensors - transducers.