Balancing of Large Rotors:

The method explained in Section 19.4.1 for thin disc may be extended for the big rotors which are balanced in situ. In this case, there are two balance planes & two measurement planes.

We select two measurement planes say A & B and two convenient balancing planes say L & R. Consider L₁ and R₁ be the initial readings of vibration levels measured respectively with phase angles γ₁ and δ₁.

The phase angles are measured along same reference through the test. Figure 10(b) illustrated the values L₁ and R₁. In the second run a trial mass TR is located at a convenient position in plane R and assume the observation respectively be L₂ and R₂ at angles γ₂ and δ₂ in the left and right planes of measurement A & B as illustrated in Figure 10(c). The difference among the readings of first run and second run shall be the effect of trial mass. Consider   and  be the effect coefficients on the right and left planes for trial

The trial mass is eliminated from plane R and place another trial mass.  in the left plane and the test is repeated. Assume L₃ and R₃ by the observation respectively at angles γ₃ and δ₃. Consider the influence coefficient for this case be

After calculating these four influence coefficients, correct balance masses may be find out. Assume the correct balance masses are respectively and for right and left planes. As the initial reading R₁ and L₁ defined the unbalance in the machine, for correcting (- R₁ ) and (- L₁ ) balancing is needed

These masses may be calculated and mounted on the balancing planes for balancing.