Single-Plane Field Balance Trial Weight

One baseline reading, one trial-weight reading, and the difference says how much weight to add and where. THE TRIAL WEIGHT IS NOT A GUESS AT THE CORRECTION, it is a probe -- it tells you how the rotor responds to a known weight at a known place. The effect vector is that response, obtained by subtracting the original reading from the trial reading as VECTORS rather than as magnitudes, and once you have it the correction is pure proportion: scale the trial weight by the ratio of the original vibration to the response, and rotate it so its effect points opposite the original. A fan reading 6.2 mils at 45 degrees, with a 10 g trial weight at 0 degrees taking it to 3.8 mils at 160 degrees, gives an effect of 8.53 at 201 degrees, a 7.27 g correction, and a 24 degree move from where the trial weight sat. Two rules keep it out of trouble. Size the trial weight to change the reading NOTICEABLY -- roughly 30% in amplitude or 30 degrees in phase; too small and the effect vector is buried in measurement noise and the answer is worthless, too large and the machine may be unsafe to run. And THE TRIAL WEIGHT COMES OFF when the correction goes on, unless the correction is deliberately computed as an adjustment to it: leaving both on is the most common way a first balance attempt makes things worse. The influence coefficient is reported because it is reusable -- on the same machine at the same speed it turns every future balance into a single reading with no trial run at all. This is the single-plane vector solve on readings the user takes. It assumes the rotor responds linearly to added weight, which holds for a rigid rotor below its first critical speed and fails near a resonance, where amplitude and phase move sharply with small speed changes and a balance done there will not hold. It does not handle two-plane or couple unbalance, which a long rotor needs and which single-plane balancing can make worse; it does not verify that the problem IS unbalance -- misalignment, looseness, a bent shaft, and a cracked rotor all show at 1x and none of them is cured by weight; and it does not address weight attachment, the safe placement radius, or whether the machine may be run in its present condition. The machine manufacturer's balancing instructions, the applicable balance quality grade, and a qualified balancing technician govern.

effect vector E = T - O by vector subtraction of the trial and original readings; correction weight = trial weight x |O| / |E|; the correction is placed by rotating the trial weight through the angle from E to the direction opposite O; influence coefficient = |E| / trial weight.

The single-plane trial-weight (influence coefficient) balance method as standard practice, by name. Linear response is assumed, which holds for a rigid rotor below its first critical speed and fails near a resonance. The machine manufacturer's balancing instructions, the applicable balance quality grade, and a qualified balancing technician govern.

Vector arithmetic on amplitude and phase readings the technician takes; no manufacturer procedure is reproduced.

Estimate. AHJ and licensed professional govern.

Field names used by the API: original_amplitude, original_phase_deg, trial_weight_g, trial_weight_angle_deg, trial_amplitude, trial_phase_deg, effect_magnitude, effect_angle_deg, correction_weight_g, correction_angle_deg, influence_coefficient

• Linear response assumed it fails near a resonance, where a balance will not holdbalancing practice
• Single plane only a long rotor needs two-plane, and single-plane can make couple unbalance worsebalancing practice
• It does not verify the fault IS unbalance misalignment, looseness and a bent shaft all show at 1xcondition monitoring practice