Calculation Parameters

ISO 1940 – Maximum permissible shaft vibration displacement




RPM






Calculation Results

Permissible Vibration Displacement:
—
Corresponding Velocity:
—
Maximum Bearing Clearance:
—
Frequency:
—

Displacement Severity Assessment:

Good: Less than 30% of calculated value
Acceptable: 30-70% of calculated value
Marginal: 70-100% of calculated value
Unacceptable: Above calculated value

How the Calculator Works

Vibration Displacement and Balance Quality

Vibration displacement is directly related to the balance quality grade through the formula:

S = (G × 1000) / (2πf)

where:

  • S — vibration displacement (μm peak-to-peak)
  • G — balance quality grade (mm/s)
  • f — rotation frequency (Hz)

Relationship Between Displacement, Velocity, and Acceleration

For sinusoidal vibration:

  • Velocity: v = 2πf × S
  • Acceleration: a = (2πf)² × S

Bearing Clearance Classes

Bearing clearances affect permissible displacement:

  • C2: Used for high precision applications
  • CN: Normal clearance for general applications
  • C3: Used when operating temperature is higher
  • C4/C5: For high temperature or heavy load applications

Measurement Types

  • Peak-to-Peak: Total displacement range (most common)
  • Peak: Maximum displacement from center position
  • RMS: Root mean square value (0.707 × peak for sine wave)

Application Guidelines

  • Lower speeds generally allow higher displacement values
  • Displacement measurement is most effective below 1000 RPM
  • Above 1000 RPM, velocity measurements are preferred
  • Above 10,000 RPM, acceleration measurements are recommended

Critical Considerations

  • Ensure probe is properly calibrated and positioned
  • Account for thermal growth when setting cold clearances
  • Consider shaft surface condition for eddy current probes
  • Monitor trends rather than absolute values for best results

Usage Examples & Value Selection Guide

Example 1: Large Slow-Speed Motor

Scenario: 500 kW motor driving a mill at low speed

  • Speed: 300 RPM
  • Balance Quality: G 6.3 (process machinery)
  • Shaft Diameter: 200 mm
  • Bearing Clearance: CN (normal)
  • Measurement: Peak-to-Peak
  • Result: S_max ≈ 126 μm p-p
  • Good condition: < 40 μm p-p
Example 2: Precision Spindle

Scenario: Machine tool spindle for precision grinding

  • Speed: 6000 RPM
  • Balance Quality: G 0.4 (precision)
  • Shaft Diameter: 60 mm
  • Bearing Clearance: C2 (small)
  • Measurement: Peak-to-Peak
  • Result: S_max ≈ 1.3 μm p-p
  • Critical: Requires precision measurement
Example 3: Turbine Generator Shaft

Scenario: Steam turbine with proximity probes

  • Speed: 3600 RPM
  • Balance Quality: G 2.5 (turbines)
  • Shaft Diameter: 400 mm
  • Bearing Clearance: C3 (hot running)
  • Measurement: Peak-to-Peak
  • Result: S_max ≈ 13 μm p-p
  • Alarm: Set at 80% = 10 μm

How to Choose Values

Speed Range Guidelines
  • < 600 RPM: Displacement measurement preferred
  • 600-1000 RPM: Either displacement or velocity
  • 1000-10000 RPM: Velocity measurement preferred
  • > 10000 RPM: Acceleration measurement recommended
Balance Quality Selection for Displacement
  • G 0.4: Precision spindles, gyroscopes (1-5 μm typical)
  • G 1: Grinding machines, small armatures (5-15 μm typical)
  • G 2.5: Machine tools, pumps, fans (15-40 μm typical)
  • G 6.3: General machinery (40-100 μm typical)
  • G 16: Large slow machines (100-250 μm typical)
Bearing Clearance Selection
  • C2:
    • High precision applications
    • Low operating temperatures
    • Light loads
  • CN (Normal):
    • General applications
    • Normal temperatures
    • Standard loads
  • C3-C5:
    • High temperature operation
    • Heavy loads
    • Thermal expansion concerns
Measurement Type Selection
  • Peak-to-Peak:
    • Standard for displacement
    • Total movement range
    • Direct bearing clearance comparison
  • Peak (0-Peak):
    • Half of peak-to-peak
    • Used in some standards
    • Stress calculations
  • RMS:
    • Energy content
    • 0.707 × peak (sine wave)
    • Statistical averaging
Probe Setup Tips
  • Gap voltage: Set to mid-range (-10V typical)
  • Probe location: 45° from vertical on each bearing
  • Surface prep: Ensure smooth, clean shaft surface
  • Runout compensation: Record and subtract electrical/mechanical runout