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An influence coefficient is a complex number that describes how a unit weight placed at a specific radius and angle affects the vibration of a rotor. It is the ratio of vibration change to the weight that caused it:

C = ΔV / W_trial

Once known, it can be used to calculate the exact correction weight needed to reduce vibration to zero (theoretically).

The process has three steps:

• Run 1: Measure the initial vibration amplitude and phase (V₀)
• Run 2: Attach a known trial weight, measure new vibration (V₁)
• Calculate: ΔV = V₁ − V₀, then correction = −m_t × V₀ / ΔV

Remove the trial weight, place the correction weight at the calculated angle, and verify with a final run.

This is normal and not a problem. An increase means the trial weight happened to be placed near the heavy spot, adding to the unbalance. The vector calculation still produces the correct correction.

However, if vibration increases by more than 3–4×, use a smaller trial weight for safety, especially on equipment with limited bearing capacity.

Yes, this is standard practice. After placing the correction weight:

• Measure the residual vibration
• Use the same influence coefficient for a trim run
• Calculate a small additional correction

Two to three iterations typically achieve the target balance quality. The influence coefficient remains valid as long as operating conditions don't change.

Key factors:

• Speed stability — measurements must be at the same RPM
• Phase reference — tachometer signal must be stable
• Thermal state — let the machine warm up consistently
• Trial weight size — should produce 20–50% vibration change
• Sensor mounting — rigid, repeatable sensor position
• Nonlinearity — very high vibration may introduce errors