Interactive tool. Apportions the rotor weight to the two correction planes for the tolerance criteria, from the mass center or the pedestal loads, and converts pedestal force readings to correction-plane unbalance vectors, or the reverse. SI or US units, with a printable record.
This calculator performs two computations from the geometry of a rotor on a hard-bearing balancing machine, entered once:
Plane weight: enter the rotor weight and the position of its mass center, or the two pedestal static loads, and it returns the pedestal loads and the portion of the rotor weight attributable to each correction plane, as a weight and as a share of the rotor weight, for use as the weight in the API 4W/N and ISO tolerance criteria.
Pedestal force conversion: enter the two pedestal force readings, magnitude and phase, and it returns the unbalance vectors in the two correction planes, or the reverse, together with the unbalance referred to each pedestal.
The calculator's results have been compared with those of a separately written program in 2,000 randomized cases, and every displayed value agreed with it to the last digit. Further tests confirmed that the plane weights sum to the rotor weight, that they equal the pedestal static loads when the correction planes lie at the pedestals, and that they are the calculator's own force conversion applied to those loads. The calculator also reproduced the results of two worked examples from a reference document.
Sample output
The calculator's output for its first example, Planes inside the span. Plane weight: a 120 kg rotor with its mass center 550 mm from pedestal 1 on a 1,000 mm span, with planes A and B 300 mm and 700 mm from pedestal 1, computed with the equations of the Each Plane's Portion of the Rotor Weight section of Low Speed Balancing Machines.
Result
Plane weight
Pedestal 1 static load W1 (kg | % of WR)
54 | 45
Pedestal 2 static load W2 (kg | % of WR)
66 | 55
Plane A weight WA (kg | % of WR)
45 | 37.5
Plane B weight WB (kg | % of WR)
75 | 62.5
Pedestal force conversion: pedestal forces of 12.366 N at 13.61° and 8.291 N at 289.14° at a balancing speed of 500 RPM, on the same geometry, converted with the equations of the Hard-Bearing Machines section.
Result
Plane unbalance
Plane A unbalance UA magnitude (g·mm)
8,000
Plane A unbalance UA phase (°)
30
Plane B unbalance UB magnitude (g·mm)
6,000
Plane B unbalance UB phase (°)
255
Unbalance referred to pedestal 1, F1/ω² (g·mm)
4,511
Unbalance referred to pedestal 2, F2/ω² (g·mm)
3,024
The printed record of the same example. Click the image to enlarge it.
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