Measurement Computing Medallion Rotate rev.2.3 - Manual (Page 35)

October 2000 Medallion Rotate Manual
35
3. Choose OK to close the Preferences dialog box.
4. Process the tachometer signal. See “Process a Tachometer Signal.”
Medallion Rotate creates the torsion file at the same time, then displays
the machine speed curve. Note this is the instantaneous speed in
degrees/second. The machine speed curve shows the torsional speed
changes as oscillations around the mean speed.
Hint: After processing, choose Preferences from the Edit menu. Clear the
check box for Create torsion file during tachometer processing unless
you are going to create more torsion files immediately. Creating the
torsion file during Tachometer processing can slow down Medallion
Rotate.
5. Close or minimize the machine
speed plot.
6. In the Channel List window, select
the torsion file (*.tor) and the
smoothed speed curve, then click
the Waterfall analysis button to
create a Waterfall plot. The
amplitude axis for the plot is in degrees/second.
Note that the torsional file includes a large DC component, equal to the
mean machine rotational speed. The amplitude of the DC component is much
greater than that of the higher order torsional vibration components, and must
be excluded.
7. Right click on the plot and select
Zoom. Then click and draw a
rectangle on the plot that excludes
the DC component. See “Zoom in
on the Time Waveform.”
8. Right click on the plot and choose
Properties. Select Viewed data
only in the Amplitude Axis tab of
the dialog box to scale the
amplitude axis to the zoomed part
of the plot. Note that the torsion
Waterfall plot shows the firing
order at 1.5 orders, and that in
general, the torsional component
driven by the firing orders is lower
at higher speeds. The first order is
the crankshaft imbalance, which increases with increasing speed. The
other peaks are harmonics of the firing order.
There is also a resonance as shown in the second plot.
Hint: To change between frequency and order cursors, right click the plot