Measurement Computing Medallion Rotate rev.2.3 - Manual (Page 29)

October 2000 Medallion Rotate Manual
29
RPM
FROM
W
ATERFALL
The RPM from Waterfall function in Medallion Rotate Plus allows you to
determine the machine speed from a waterfall file. If you do not have a
tachometer signal, or the signal is extremely noisy, you can use other data to
create an RPM curve that describes the speed of the machine over time.
Medallion Rotate can use this smoothed speed curve in the same ways as
a speed curve generated from a tachometer signal. You can use this speed
curve to diagnose some problems directly. You can also use the speed curve
along with other data, such as vibration, as an input for additional
sophisticated Medallion Rotate analysis techniques.
A
PPLICATIONS
The RPM from Waterfall function is applicable when you have a time
waveform from a data channel, but no tachometer signal or a noisy signal.
There may not be a tachometer available, or it may be impractical to use a
tachometer or other speed sensor on the machine. In some cases, the RPM from
Waterfall function may produce a better speed curve than a tachometer.
I
NPUT
When collecting the non-tachometer data (vibration, temperature, …), note
the following:
• If you want to see low frequency data in the Waterfall analysis, make
sure that the high pass filter setting in your analyzer is not excluding
the desired low frequencies.
• The sample rate in the analyzer must be at least 2.5 times the maximum
frequency of interest to avoid aliasing.
• The choice of window function for analysis depends on the type of
resolution you need (amplitude or frequency resolution). Since the
RPM from Waterfall function depends more on the position of the
spectral peaks than on the amplitude, the Hamming window is a good
default choice.
E
XAMPLE
This example uses the RPMFromWaterfallDemo.wat file included with
Medallion Rotate Plus. You can also use any waterfall file generated by
Medallion Rotate using Waterfall analysis (see “Waterfall Analysis” ).
1. In the Channel List Window select
the RPMFromWaterfallDemo.wat
file, then select the waterfall
channel. You can display the
Waterfall by clicking on the Plot
button.