also provide the added benefit of a check for accuracy of readings. Figure 14 is an example of
the form used to record the readings.
Where plumb wires are being used, care should be taken to ensure there are no kinks in the wires.
With the weights installed, the entire length of each wire should be checked by feel for any bend
or kinks. If any kink can be felt, the wire should be replaced. While the wires don't have to be
an equal distance from the shaft, they should be within ½ inch so that they are within the range of
the micrometer head. The brackets for the oil buckets should be sturdy and secure to prevent
spilling oil while taking readings. The weights should be heavy enough to keep the wires very
taut but not so heavy as to consistently break the plumb wires. The weights, when suspended in
the oil, should be completely submerged, but they should not touch the bottom or the sides of the
bucket. The steel banding material placed around the shaft at the reading elevations should be
level, and the distance from the coupling should be rechecked occasionally during the alignment
process to make sure it corresponds with the dimensions used for plotting.
4.2 Hamar Laser System
The Hamar laser system uses a laser beam to replace the wire and a micrometer adjustable target
attached directly to the shaft with a magnetic base to measure the distance from the shaft to the
laser (photo 4). There are two photoelectric cells mounted next to each other in the target with
opposite polarity. When the laser beam is perfectly centered between the two cells, the voltage
output of the target is zero. Four rigid steel bases are installed 90 degrees apart around the shaft
in the turbine pit corresponding to north, south, east and west. Magnetic bases on the laser attach
it to the steel bases and precision levels in the base of the laser act as the reference for plumb.
The laser must be moved and releveled for each set of readings (north, south, etc.). The readings
are recorded and the shaft centerline plotted in the same manner as with the wires.
The foremost problem encountered with the Hamar laser system is vibration from the mounting
baseplate. Any vibration of the baseplate will be transferred to the laser and be magnified as the
laser beam projects upward, making the top reading very unstable. Very solid base plates, rigidly
attached to the head cover or the turbine bearing bracket, limit the vibration transferred to the
laser. To prevent errors from the laser not being perfectly verical, the same end of the laser
should always be pointed toward the shaft. In this way, any error in verticality will be subtracted
out in the worksheet the same way as a taper in the shaft is corrected.
Another critical item to observe is the level. The laser must be leveled precisely initially and
rechecked frequently to obtain accurate measurements.