Section 3 — Sensors
41
• In addition to the existing Tach Trigger and Off tachometer
modes, it is possible to set the mode to RPM Only for all
instruments and threshold levels (standard and Keyphasor). You
can use the RPM mode when you need the tachometer to
record machine running speed, but do not require tach
triggering (e.g. when you take coast-down recordings on a
machine with rolling element bearings). The disadvantage of
selecting Tach Triggering is that spectral averaging will average
away the non-synchronous peaks. This is not ideal when you
are trying to find rolling–element bearing faults. Additionally, in
Tach Trigger mode, the tach signal must be present. This means
the recording cannot be completed if the tach is disconnected
or faulty. In contrast, RPM Only mode records the speed if this is
available. Consequently, if the tach signal is not present, the
recording is still completed and its RPM value is set to the
machine’s default speed.
The additional Keyphasor thresholds are available for the following
measurement types:
• Spectrum/Waveform
• Demodulation
• Time synchronous Averaging
• Bump Test
• Coast Down/Run-up
• Long Time Waveform
• Orbit Plot
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