Field Balancing: Single- and Two-Plane

The machine is not dismantled and production is not interrupted for disassembly. In its installed state, the vibration caused by rotor unbalance is measured and the mass, mounting radius and mounting angle of the correction weight are calculated. One or a few weight additions bring the vibration within the permitted range. Single-plane and two-plane modes cover short disc-type rotors and longer rotors.

When to balance: when 1× dominates the measured vibration (usually more than 60 % of the total), balancing is the most direct and fastest remedy — at installation and commissioning, after overhaul, or after a vibration alarm.

Consequences of unbalance

Unbalanced mass produces a centrifugal force during rotation and excites vibration at running speed. Long-term excessive 1× vibration causes:

1. Shorter bearing life: vibration reaches the bearings, rolling elements and races suffer alternating impacts and fatigue spalling occurs earlier.
2. Faster seal and coupling damage: vibration causes misalignment, seal rubbing and diaphragm coupling fatigue.
3. Excessive noise: 1× vibration produces low-frequency noise affecting the workplace.
4. Variable product quality: spindle and precision equipment vibration appears directly in surface roughness.
5. Structural fatigue and safety risk: prolonged resonance or severe unbalance can lead to blade fracture and other serious failures.

Value of field balancing

• No disassembly: the rotor is not removed for a balancing machine, avoiding realignment and added errors.
• Short downtime: usually two to four starts and stops, saving time and cost compared with factory balancing.
• Quantified correction: the result states how many grams to add and at which angle.
• Documented result: balance quality is evaluated to the standard and can be accepted and archived.

Unbalance and 1× response

A rotor with unbalance U (in g·mm, mass × radius) produces a centrifugal force proportional to the square of speed and excites vibration at running speed. In the linear range, the 1× vibration vector V at a measurement point is proportional to U:

V = α × U

α is the influence coefficient: the 1× vibration (amplitude and phase) at the measurement point per g·mm of unbalance. With α known, the unbalance and the correction weight follow.

Influence coefficient method: single plane

1. Record the original 1× vibration V0 (amplitude and phase).
2. Add a known trial weight T (g·mm, mass × radius, at a known angle) in the correction plane and record the 1× vibration V1.
3. The change caused by the trial weight is V1 − V0, giving the influence coefficient and the correction vector.

α = (V1 − V0) / T Uc = −V0 / α

The software gives the mass, radius and angle of the correction weight, with a choice of removing or keeping the trial weight (when it is kept, the target vector automatically subtracts the installed trial weight).

Influence coefficient method: two planes

On a long rotor the two correction planes interact: a weight in plane 1 changes the vibration at both points A and B (cross-coupling). A 2 × 2 influence coefficient matrix describes this:

[V_A; V_B] = [α11 α12; α21 α22] × [U1; U2]

Three runs — original, trial weight 1 and trial weight 2 — give the complete matrix. The linear equations are solved together for the correction of each plane, which removes the coupling mathematically. The predicted residual vibration of both planes is shown for checking.

Tachometer phase reference

The angle of the unbalance needs a common 0° reference, provided by a tachometer sensor aimed at reflective tape or a keyway on the shaft. For every frame, the software detects the position of the tachometer pulse edge and converts the vibration phase to a common coordinate system with the tachometer at 0°. This ensures:

• A consistent phase reference for every measurement and every start, so data can be compared and subtracted.
• An automatic speed consistency check; abnormal frames are rejected before the calculation, preventing absurd results.
• Automatic detection of a wrongly connected tachometer channel (for example a vibration signal), with a message.

This is the key to accurate and stable field balancing.

Balance quality grade and permissible residual unbalance (ISO 21940-11)

With rotor mass m (kg), maximum service speed n (rpm) and target grade G (for example G2.5):

e_per = 9549 × G / n (µm, permissible eccentricity) U_per = e_per × m (g·mm, permissible residual unbalance)

Example: rotor mass 50 kg, speed 1480 rpm, grade G2.5: e_per = 9549 × 2.5 / 1480 ≈ 16.1 µm and U_per = 16.1 × 50 ≈ 806.5 g·mm. After the grade and rotor mass are entered, the permissible residual unbalance is shown; after the calculation, residual unbalance ≤ permissible value means the rotor meets the grade.

Split-weight installation plan

In the field the calculated weight often cannot be installed as one piece, for example because it is too heavy or the position is obstructed.

• Select 1 to 4 weights and the target vector is divided automatically, with mass, radius and angle for each.
• Target, current and remaining values update as any weight's mass, radius or angle is edited.
• Double-click to recalculate: if a weight can only be mounted at 45°, double-click the mass field to get the mass required at 45°.
• In two-plane balancing, separate plans are given for plane 1 and plane 2.

The plan turns the calculation directly into installation instructions and reduces conversion errors and wrong angles.

1. Guided procedure: record original, add trial weight, calculate correction, install and verify — beginners can follow the steps without balancing machine experience.
2. Stable results: frame-by-frame phase alignment, speed consistency checks and tachometer miswiring detection keep repeated measurements consistent.
3. Single and two planes in one system, with cross-coupling resolved, so long rotors are balanced without a separate two-plane instrument.
4. Split-weight plans: 1–4 weights, divided automatically and recalculated for site constraints.
5. Virtual rotor demonstration for training and customer demonstrations without a rotor.
6. Standard built in: ISO 21940-11 permissible values calculated automatically for reports and acceptance.
7. Eight-channel acquisition platform shared with T8 vibration and acoustic analysis — vibration meter, spectrum analyzer and balancer in one.
8. Every step recorded in tables, with report output for customers and audits.

Preparation

1. Sensors: mount the vibration sensor (acceleration, velocity or displacement) by magnet or stud on the bearing housing, radial horizontal or vertical, and do not move it during the procedure. Two-plane balancing needs two points in the same direction (both horizontal or both vertical), each near the bearing closest to its correction plane.
2. Tachometer: aim the optical sensor at reflective tape (or a keyway) to produce one pulse per revolution; the tape position is 0°.
3. Wiring: point A to channel A, point B to channel B for two planes, and the tachometer to the tachometer channel (any channel can be assigned).

Settings

Single-plane procedure

1. Record the original vibration once the machine runs steadily; the table records 1× amplitude and phase.
2. Stop and add a known trial weight in the correction plane. It should change the vibration by at least 30 % of the original (the software suggests a trial mass). Enter mass, radius and angle (measured counter-clockwise from the tachometer 0°).
3. Record again and calculate the correction; the correction mass and angle appear with the vector diagram and parameter table.
4. Install the correction according to the selected method (remove or keep the trial weight; if kept, it is already subtracted), record again and compare the residual vibration with the permissible value.

Two-plane procedure

1. Record the original vibration at both points.
2. Stop, add trial weight 1 in plane 1, run and record, stop and remove trial weight 1.
3. Add trial weight 2 in plane 2, run and record, stop and remove trial weight 2.
4. Calculate; the software solves both planes together and gives the correction mass and angle for each (values marked * are equivalent single-plane estimates; use the two-plane results for the correction).
5. Install both corrections in their planes and record again to verify. A rotor diagram shows the trial and correction positions in both planes and updates with the result.

Using the split-weight plan

1. After the calculation the installation plan appears; select the number of weights (1–4) and the target vector is divided automatically.
2. Edit any weight's mass, radius or angle; current and remaining values update, and “balanced” is shown when the remainder approaches zero.
3. If the angle is restricted on site, change it to a possible angle and double-click the mass field; the software calculates the mass needed at that radius.
4. In two-plane balancing, switch between plane 1 and plane 2 at the top of the panel.

Virtual rotor (training)

With the virtual rotor enabled, the software generates a rotor with a random initial unbalance; trial and correction weights affect the response according to real physics, including two-plane coupling. The complete sequence — record, add trial weight, calculate, apply the simulated correction and verify the drop in residual vibration — can be practiced without equipment. Reset the rotor to start again.

A fan rotor of 50 kg at 1480 rpm (24.67 Hz) with grade G2.5 is used as the example. The software shows the following items:

Interpreting the result

• Residual unbalance ≤ permissible value: the rotor meets the grade and the report can be issued.
• At constant speed the phase should be stable (typically within ±5° after tachometer alignment); if it fluctuates strongly, check the reflective tape and sensor alignment first.
• If the trial weight changes amplitude and phase by less than 10 %, the trial weight is too light and the influence coefficient is unreliable; use a heavier trial weight and measure again.
• If 1× drops clearly after correction but the total vibration stays high, other faults such as misalignment or looseness are present; continue with the spectrum and diagnosis functions of the platform.