PRÜFTECHNIK VIBXPERT II, Operating Instructions Manual

Page: 132 / 176

5-12
VIBXPER
T II 05.2012
Shaft centerline plot
A shaft centerline plot records the movement of the shaft axis* in a
journal bearing while the machine is running up or coasting down
(e.g. turbine). Conclusions can be drawn from the shaft centerline
plot on the fault conditions - such as oil whirl or oil whip in journal
bearings.
A description of the measurement procedure with VIBXPERT can
be found in the Technical Information CM # 18 'Analysis of radial
shaft movement in journal bearings’ - available free on our website.
A shaft centerline plot can be set up via the following task:
2-
channel coastdown
-
phase
,
meas
.
quantity
:
displacement
Parameters set up in the measurement task manager (see below)
• As the measurement task, select 'Dual Amp. Startup/Coastdown
User' (see p. 5-7).
• As the measurement setup, select 'Dual Coast Down User'.
• Set the following parameters in the measurement setup:
- m
easurement quantity
= Vibration displacement
- l
ower frequency
= DC
• In the sensor setup, select the displacement sensors (e.g. VIB
6.640).
Requirements for correctly interpreting the results
- The sensors are installed at an angle of 90° to each other.
- The shaft always turns from sensor A to sensor B. The position of
the sensor relative to the direction of rotation can be adjusted after
measurement.
- The static shaft position can be displayed as an offset in the shaft
centerline plot.
* The movement of the shaft axis at a
constant
rpm is recorded with an orbit
plot (p. 5-16).
Channel A
Channel B
RPM
Shaft centerline plot
Setups in the task manager Parameters in the meas. setup Results display
Measurement tasks

Note