Why is three-gauge alignment generally used for machinery units, and what is the calculation method?

Large-scale units generally use sliding bearings for their drive motors; when aligning the rotor, the motor side of the bearing allows for axial movement, so three-indicator methods are used to compensate for this axial movement. The calculation methods are specified in the standards for machine installation. Such as SH3538－2005.

Using three gauges for alignment of the unit is mainly aimed at eliminating the effect of shaft play. Generally, the value for the upper-upper axis direction minus the value for the lower-lower axis direction divided by 2 gives the amount of opening; the values for the left and right sides are the same. The radial value can then be determined using the values from those two gauges. Once these values are obtained, they can be plugged into the alignment formula to complete the process.

I agree with what was said on the 2nd floor: for Table 3, align it in the center. Among the two axial tables, one serves as the main table while the other is the auxiliary table; the actual value is obtained by subtracting the value from the auxiliary table from that of the main table (this helps to eliminate axial movement that occurs during shaft rotation). :)

It’s hardly used these days; the three-meter method has certain errors that cannot be eliminated

Actually, using three instruments is quite reliable; on the contrary, using more advanced devices such as laser aligners results in greater errors. We usually first use a laser aligner to make the adjustments, and then verify them with the three instruments.

The three-gauge measurement method involves placing two dial indicators symmetrically at equal distances from the axis center. While measuring the radial and axial readings in one orientation, the axial reading is taken in the opposite orientation; by thus measuring the axial readings in both opposing orientations simultaneously, the effect of axial movement of the shaft during turning can be eliminated. Based on the measurement results, the average of the axial readings taken at the two measurement angles of 0°–180° and 180°–0° is calculated, namely s1 = (s1’ + s1’’) / 2 and s3 = (s3’ + s3’’) / 2. The average of the axial readings taken at the two measurement angles of 90°–270° and 270°–90° is also calculated, namely s2 = (s2’ + s2’’) / 2 and s4 = (s4’ + s4’’) / 2. These four averages, s1, s2, s3, and s4, serve as the axial readings for each measurement angle. Together with the four radial readings, a1, a2, a3, and a4, they are recorded in the same graph. By analyzing the data in this graph, the offset of the coupling can be determined, and adjustments can be made accordingly. This measurement method offers high precision and is suitable for precision or high-speed machines that require accurate alignment, such as steam turbines and centrifugal compressors. This post was last edited by domolee on 2009-3-1 at 19:50

:handshake Thank you, that’s very detailed

The three-table alignment method is relatively accurate for alignment, but it is essential to ensure the stiffness of the alignment frame during use.