Make sure you are getting good repeatable measurement data before you make corrections. This particular alignment, both shaft were hard to turn and we had to use an overhead crane on the generator shaft and a turn bar on the steam turbine shaft. Using a turning bar or crane to rotate the shaft can induce error into the reading because of shaft deflection.
I used pass mode for this application and not only do I check repeatability of measurements but also check the standard deviation of points taken(the standard deviation is a measure of how spread out numbers are from the mean). Rotalign sensors measure rotational centerlines by using many points that form an ellipse. If some of the points are corrupted the Rotalign Ultra iS’s intelligent sensing knows not to use those points as part of the measurement therefore making it more accurate. The Rotalign is the only system on the market that not only monitors standard deviation, it makes corrections to the points taken based on those values, making it the most accurate system on the market.
I try to get as much rotation as possible with roughly 10-15 degrees rotation between each measurement points taken. In order to get as much rotation as possible, try to use brackets with posts just tall enough to shoot over the coupling or you can use specialty bolt hole brackets. After the corrections were made, I made sure to leave the Rotalign Ultra iS in “Live Move” as we tighten the anchor bolts. The Rotalign Ultra iS in the only system on the market that allows you to watch both the horizontal and vertical planes in real time. By watching alignment conditions during final torque we can make sure that the alignment stays within tolerance.
Always take a final reading to confirm that the alignment is in tolerance. The only way to measure the rotational centerlines of shafts is to rotate them. Never trust the live move as your final result regardless of what laser alignment system you use!
Alignment completed to spec and full alignment report printed to PDF directly from the Rotalign Ultra iS to a thumb drive. All vibration levels were good during startup and another alignment completed using the Rotalign Ultra iS.
Much thanks to the Local Millwrights that assisted on this alignment. Some of the guys had over 20 years experience using versions of the Rotalign. The Rotalign is the tool of choice and it is what is taught at the Local Millwright Training Centers.