ISO 20816-3:2022 is an international standard for measurement and evaluation of vibration on industrial machinery with power rating above 15 kW and operating speeds between 120 and 30,000 r/min. It supersedes ISO 10816-3 and ISO 7919-3.

What are vibration zones A, B, C, and D?

Zone A: Newly commissioned machines in optimal condition. Zone B: Acceptable for unrestricted long-term operation. Zone C: Not suitable for continuous operation; remedial action required. Zone D: Vibration severe enough to cause damage; immediate action needed.

How to classify machine as Group 1 or Group 2?

Group 1: Power > 300 kW or electric machines with shaft height H > 315 mm. Group 2: Power 15–300 kW or electric machines with shaft height 160 < H ≤ 315 mm.

What is the difference between rigid and flexible foundation?

A foundation is rigid if the lowest natural frequency of the machine-foundation system exceeds the main excitation frequency by at least 25%. All other foundations are flexible.

ISO 20816-3: Vibration Limits for Industrial Machines — Calculator & Guide

ISO 20816-3: Vibration Limits for Industrial Machines

Interactive calculator and comprehensive technical guide for vibration zone assessment of industrial machinery per ISO 20816-3:2022. Covers housing vibration, shaft vibration, measurement methodology, and field balancing with Balanset-1A.

⚙ Table A.1 — Group 1 Machines (Large: >300 kW or H>315 mm)

RMS vibration velocity (mm/s) and displacement (μm) · 10–1000 Hz · Non-rotating parts

Zone	Rigid — Vel. (mm/s)	Rigid — Disp. (μm)	Flexible — Vel. (mm/s)	Flexible — Disp. (μm)
A — Good	< 2.3	< 29	< 3.5	< 45
B — Acceptable	2.3 – 4.5	29 – 57	3.5 – 7.1	45 – 90
C — Limited	4.5 – 7.1	57 – 90	7.1 – 11.0	90 – 140
D — Dangerous	> 7.1	> 90	> 11.0	> 140

⚙ Table A.2 — Group 2 Machines (Medium: 15–300 kW or H=160–315 mm)

RMS vibration velocity (mm/s) and displacement (μm) · 10–1000 Hz · Non-rotating parts

Zone	Rigid — Vel. (mm/s)	Rigid — Disp. (μm)	Flexible — Vel. (mm/s)	Flexible — Disp. (μm)
A — Good	< 1.4	< 22	< 2.3	< 37
B — Acceptable	1.4 – 2.8	22 – 45	2.3 – 4.5	37 – 71
C — Limited	2.8 – 4.5	45 – 71	4.5 – 7.1	71 – 113
D — Dangerous	> 4.5	> 71	> 7.1	> 113

⚙ Annex B — Shaft Vibration Limits (Displacement)

Peak-to-peak shaft displacement S(p-p) in μm · Measured with proximity probes

Zone Boundary	Formula	@ 1500 rpm	@ 3000 rpm	@ 6000 rpm
A/B	4800 / √n	124	88	62
B/C	9000 / √n	232	164	116
C/D	13200 / √n	341	241	170

Balanset-1A full kit portable balancer and vibration analyzer

Devices

Portable balancer & Vibration analyzer Balanset-1A

Parts

Vibration sensor

Parts

Optical Sensor (Laser Tachometer)

Vibromera rotor balancing kit: carry case, multi-channel signal conditioner, handheld analyzer, magnetic base, vibration sensors, and coiled cables.

Devices

Balanset-4

Parts

Magnetic Stand Insize-60-kgf

Parts

Reflective tape

Balanset-1A kit contents with interface unit, sensors, tachometer and accessories

Devices

Dynamic balancer “Balanset-1A” OEM

Vibration Zone Assessment Calculator

Enter machine parameters and measured vibration to determine condition zone per ISO 20816-3

Machine Power Rating

Minimum 15 kW for this standard

Operating Speed

r/min

120 – 30,000 r/min

Shaft Height (electric machines)

IEC 60072 shaft centerline to mounting plane. Leave blank if unknown.

Foundation Type Based on lowest natural frequency of machine-foundation system

Measurement Type

Bearing Type

Measured Velocity (RMS)

mm/s

Broadband 10–1000 Hz (or 2–1000 Hz for ≤600 r/min)

Measured Displacement (RMS) — optional

μm

Required for low-speed machines (≤600 r/min)

Assessment Results

Machine Classification —

Foundation Type —

Measured Value —

Zone Boundaries Applied

Boundary	Velocity (mm/s)	Displacement (μm)
A/B	—	—
B/C	—	—
C/D	—	—

Shaft Vibration Limits (Calculated)

Boundary	Formula	S(p-p) μm
A/B	4800/√n	—
B/C	9000/√n	—
C/D	13200/√n	—

Zone: —

Recommendation: —

1. Scope & Applicable Equipment

ISO 20816-3:2022 establishes guidance for evaluating vibration condition of industrial equipment with power rating above 15 kW and rotational speeds from 120 to 30,000 r/min. Assessment is based on measurements of vibration on non-rotating parts and on rotating shafts under normal operating conditions.

This Standard Applies To:

Steam turbines and generators with power up to 40 MW
Rotary compressors (centrifugal, axial)
Industrial gas turbines with power up to 3 MW
Electric motors of all types with flexible shaft coupling
Rolling mills and rolling stands
Fans and blowers (see note below)
Conveyors, variable-speed couplings, turbo-fan engines

Notes on Specific Equipment

Steam/gas turbines >40 MW at 1500/1800/3000/3600 r/min → use ISO 20816-2. Gas turbines >3 MW → use ISO 20816-4. Fans: Criteria generally apply only to fans >300 kW or on rigid foundations. For other fans, agree criteria between manufacturer and customer (see also ISO 14694).

This Standard Does NOT Apply To:

Reciprocating machines → ISO 10816-6 / ISO 20816-8
Rotodynamic pumps with built-in motors → ISO 10816-7
Hydraulic power stations → ISO 20816-5
Positive displacement compressors, submersible pumps
Wind turbines → ISO 10816-21

Critical Limitation

Requirements apply only to vibration produced by the machine itself, not to externally induced vibration transmitted through foundations. Always verify and correct for background vibration.

2. Machine Classification

Machine vibration condition is assessed depending on machine type, rated power or shaft height, and foundation rigidity.

Classification by Power / Shaft Height

Group 1 — Large Machines

Power rating > 300 kW, OR electric machines with shaft height H > 315 mm
Typically equipped with journal (sleeve) bearings
Operating speeds 120 to 30,000 r/min

Group 2 — Medium Machines

Power rating 15 – 300 kW, OR electric machines with 160 < H ≤ 315 mm
Typically equipped with rolling element bearings
Operating speeds generally > 600 r/min

Classification by Foundation Rigidity

A foundation is rigid if the lowest natural frequency of the machine-foundation system in the measurement direction exceeds the main excitation frequency by at least 25%. All others are flexible.

Rigid criterion: f_{n(machine+foundation)} ≥ 1.25 × f_excitation

Direction-Dependent Classification

A foundation may be rigid in one direction and flexible in another. For example, rigid vertically but flexible horizontally. Evaluate each direction separately using appropriate limits.

3. Understanding Zones A–D

Four vibration condition zones are established for qualitative assessment and decision-making:

Zone A — New / Excellent

Newly commissioned machines typically fall here. Represents optimal dynamic condition. Not all new machines achieve Zone A — striving below A/B may yield minimal benefit at high cost.

Zone B — Acceptable

Suitable for unrestricted long-term operation. Continue routine monitoring. This is the normal operating condition for well-maintained equipment.

Zone C — Limited Operation

Not suitable for continuous long-term operation. Plan remedial action. May operate for a limited period until repair opportunity arises. Increase monitoring frequency.

Zone D — Dangerous

Vibration severe enough to cause damage. Immediate action required: reduce vibration or stop the machine. Continued operation risks catastrophic failure.

4. Evaluation Criteria

Criterion I — Absolute Magnitude

The maximum measured broadband RMS vibration (velocity for housing, displacement p-p for shaft) is compared with zone boundary values for the given machine group and support type. This criterion protects against excessive dynamic loads on bearings, unacceptable radial clearance consumption, and excessive vibration transmitted to the foundation.

Criterion II — Change from Baseline

Even if vibration remains in Zone B, a significant change from the established baseline indicates developing problems and requires investigation.

The 25% Rule

A vibration change is considered significant if it exceeds 25% of the B/C boundary value, regardless of current absolute level. This applies to both increases and decreases.

Example: For Group 1 rigid foundation, B/C = 4.5 mm/s. A change > 1.125 mm/s from baseline is significant and requires investigation.

Acceptance Criteria for New Machines

Zone boundaries are not acceptance criteria by default. Acceptance testing limits must be agreed between supplier and customer. Typical recommendation: new machine vibration should not exceed 1.25 × A/B boundary.

5. Measurement Best Practices

Sensor Location

Mount on bearing housings or pedestals — not on thin-walled covers or flexible surfaces
Use two mutually perpendicular radial directions at each bearing
For horizontal machines, one direction is typically vertical
Avoid locations with local resonances — compare readings at nearby points
If direct access to bearing impossible, use a point with rigid mechanical connection

Operating Conditions

Measure in steady-state operation at nominal speed and load
Allow rotor and bearings to reach thermal equilibrium (typically 30–60 min)
For variable-speed/load machines, measure at all characteristic operating points, use the maximum
Document conditions: speed, load, temperatures, pressures

Frequency Range

Application	Lower Limit	Upper Limit	Notes
Standard broadband	10 Hz	1000 Hz	Most industrial machinery (>600 r/min)
Low-speed (≤600 r/min)	2 Hz	1000 Hz	Must capture 1× running speed
Shaft vibration	—	≥ 3.5 × f_max	Per ISO 10817-1
Diagnostics	0.2 × f_min	2.5 × f_excit	Extended, up to 10,000 Hz

Background Vibration

25% Rule for Background

If stopped-machine vibration exceeds 25% of operating vibration OR 25% of Zone B/C boundary, corrections are needed:

V_machine = √(V_measured² − V_background²)

If background exceeds these thresholds, simple subtraction is invalid — investigate external sources.

6. Housing Vibration Limits (Annex A)

The primary monitored parameter is RMS vibration velocity. Zone boundary values for Groups 1 and 2 are presented in Tables A.1 and A.2 above. Key notes:

For machines with rotor speed below 600 r/min, both velocity and displacement criteria apply. The frequency band extends to 2–1000 Hz.
Group 1 displacement is derived from velocity at reference frequency 12.5 Hz
Group 2 displacement is derived from velocity at reference frequency 10 Hz
The worst-case zone (from velocity or displacement) governs

7. Shaft Vibration Limits (Annex B)

For shaft relative vibration measured with proximity probes, zone boundaries are expressed as peak-to-peak displacement S(p-p) in μm, inversely proportional to √n:

A/B: S(p-p) = 4800 / √n
B/C: S(p-p) = 9000 / √n
C/D: S(p-p) = 13200 / √n
where n = max operating speed in r/min, min 600 for calculation

Bearing Clearance Limitation (Annex C)

For journal bearings, shaft vibration zone boundaries must be checked against actual bearing clearance. If formula-calculated limits exceed clearance, use clearance-based limits:

A/B: 0.4 × clearance
B/C: 0.6 × clearance
C/D: 0.7 × clearance

8. WARNING & TRIP Alarm Levels

WARNING = Baseline + 0.25 × (B/C boundary), typically ≤ 1.25 × B/C

TRIP = within Zone C or D, typically ≤ 1.25 × (C/D boundary)

Level	Basis	Setting	Adjustable?
WARNING	Machine-specific baseline	Baseline + 25% of B/C	Yes — adjust with baseline changes
TRIP	Mechanical integrity	Within Zone C/D, ≤ 1.25 × C/D	No — same for similar machines

9. Transient Operation

Zone boundaries apply to steady-state operation. During run-up, coast-down, or passage through critical speeds, higher vibration is expected.

Speed % of Rated	Housing Limit	Shaft Limit	Notes
< 20%	See note	1.5 × C/D	Displacement may dominate
20% – 90%	1.0 × C/D	1.5 × C/D	Critical speed passage allowed
> 90%	1.0 × C/D	1.0 × C/D	Approaching steady-state

If vibration remains high after reaching operating speed, it indicates a persistent fault, not a transient resonance.

10. Physics & Signal Processing

Displacement–Velocity–Acceleration

For sinusoidal vibration at frequency f (Hz):

Velocity: V_peak = 2πf × D_peak
Acceleration: A_peak = (2πf)² × D_peak = 2πf × V_peak

At low frequencies (<10 Hz): displacement is the critical parameter
At mid frequencies (10–1000 Hz): velocity correlates with energy — frequency-independent
At high frequencies (>1000 Hz): acceleration becomes dominant

RMS vs Peak

V_RMS = V_peak / √2 ≈ 0.707 × V_peak
V_p-p = 2 × V_peak ≈ 2.828 × V_RMS

Broadband RMS (Overall)

V_RMS(total) = √(V²₁ + V²₂ + ... + V²_n)

This "Overall" value is what vibration analyzers display and what ISO 20816-3 uses for zone evaluation.

Low-Speed Problem (Annex D)

At constant velocity of 4.5 mm/s, displacement grows dramatically with decreasing speed:

Speed (rpm)	Freq (Hz)	Velocity (mm/s)	Displacement (μm peak)
3600	60	4.5	12
1800	30	4.5	24
600	10	4.5	72
120	2	4.5	358

This is why the standard requires both velocity and displacement criteria for machines ≤600 r/min.

11. Influence Coefficient Balancing

When unbalance is diagnosed (high 1× vibration, stable phase), the influence coefficient method calculates precise correction weights:

Influence coefficient: α = (V_trial − V_initial) / M_trial

Correction mass: M_corr = −V_initial / α

Single-Plane Procedure (3 runs)

Initial run: Measure A₀ = 6.2 mm/s at φ₀ = 45°
Trial weight: Add 20 g at 0°. Measure A₁ = 4.1 mm/s at φ₁ = 110°
Calculate: Software computes correction = 28.5 g at 215°
Apply & verify: Remove trial, add 28.5 g at 215°. Final: 1.1 mm/s → Zone A

The Balanset-1A performs all vector math automatically, guiding the technician through each step.

12. Case Studies

Case Study 1

Misdiagnosis Avoided Through Dual Measurement

Machine: 5 MW steam turbine, 3000 rpm, journal bearings.

Situation: Housing vibration = 3.0 mm/s (Zone B). But shaft vibration = 180 μm p-p. Annex B limit B/C = 164 μm → Shaft in Zone C!

Root cause: Oil film instability (oil whirl). Heavy pedestal damped housing motion. Relying only on housing measurement would have missed the condition.

Action: Adjusted oil supply pressure, re-shimmed bearing. Shaft vibration reduced to 90 μm (Zone A).

✓ Zone A achieved — oil whirl eliminated

Case Study 2

Balancing Saves a Critical Fan

Machine: 200 kW induced draft fan, 980 rpm, flexible coupling.

Initial: Vibration = 7.8 mm/s (Zone D). Plant considering emergency shutdown ($50,000, 3-day outage).

Diagnosis: FFT shows 1× = 7.5 mm/s. Phase stable → Unbalance, not bearing damage.

Action: Two-plane balancing with Balanset-1A, 4 hours on-site. Final = 1.6 mm/s (Zone A).

✓ $50,000 saved — avoided unnecessary shutdown

Case Study 3

Zone D Pump — Balancing Won't Help

Machine: 200 kW feed pump, rigid foundation. RMS = 5.0 mm/s → Zone D.

Diagnosis: FFT shows harmonic forest and high noise floor. 1× peak low relative to total. Not unbalance.

Root cause: Bearing degradation + cavitation. Required mechanical overhaul.

✗ Immediate shutdown required — mechanical failure

13. Common Mistakes

Critical Errors to Avoid

1. Wrong classification. A 250 kW motor with H=280 mm is Group 2 (not Group 1). Using Group 1 limits (more lenient) permits excessive vibration.

2. Wrong foundation type. Not all concrete foundations are "rigid." A turbogenerator on concrete may be flexible if system natural frequency is near running speed. Verify by calculation or impact testing.

3. Ignoring background vibration. A pump reading 3.5 mm/s with 2.0 mm/s from an adjacent compressor through the floor: actual pump contribution is only ~1.5 mm/s. Always measure with machine stopped.

4. Peak instead of RMS. ISO 20816-3 requires RMS. Peak ≈ 1.414 × RMS. Using peak values directly overestimates severity by ~40%.

5. Neglecting Criterion II. Fan jumps from 1.5 to 2.5 mm/s (both Zone B). Change = 1.0 mm/s vs threshold 1.125 mm/s (25% of B/C=4.5). Close to threshold — investigate!

6. Wrong frequency range. A 400 rpm mill with 10–1000 Hz filter: running frequency = 6.67 Hz is below the filter! Use 2–1000 Hz for machines ≤600 r/min.

7. Measuring on thin walls. Accelerometer on fan casing sheet metal gives 10× higher readings than actual bearing vibration. Always mount on bearing cap or pedestal.

14. Complete Assessment Workflow

Step-by-Step Procedure

Identify machine: Record type, model, rated power, speed range
Classify: Determine Group (1 or 2) from power rating or shaft height H
Assess foundation: Measure/calculate f_n of machine-foundation system vs f_run
Select zone boundaries from standard for group + foundation type
Set up instruments: Mount sensors on bearing housings, configure frequency range
Background check: Measure vibration with machine stopped
Operating measurement: Reach thermal equilibrium, steady-state, measure RMS velocity
Background correction: Apply energy subtraction if threshold exceeded
Zone classification (Criterion I): Compare maximum RMS to boundaries
Trend analysis (Criterion II): Calculate change from baseline, check 25% rule
Spectral diagnosis: If needed, use FFT to identify fault type
Corrective action: Zone A → baseline; B → monitor; C → plan repair; D → immediate action
Balance if unbalance diagnosed: Use Balanset-1A influence coefficient method
Document: Report with before/after spectra, zone classification, actions taken

🔧 Balanset-1A — Portable Vibration Analyzer & Field Balancer

The Balanset-1A is a precision instrument that directly supports ISO 20816-3 requirements for vibration measurement and assessment:

Vibration measurement: Velocity (mm/s RMS), displacement, acceleration — all ISO 20816-3 parameters
Frequency range: 5 Hz – 550 Hz (standard), expandable — covers 2–1000 Hz requirement
Single-plane and two-plane balancing: Reduce vibration to Zone A/B levels
Phase measurement: ±1° accuracy for balancing and vector analysis
RPM range: 150 to 60,000 rpm — fully covers ISO 20816-3 scope
FFT spectrum: Identify fault types (1×, 2×, harmonics, bearing defects)
Report generation: Document measurements for compliance records

Learn More About Balanset-1A →

15. Reference Standards

Normative References

Standard	Title
ISO 2041	Mechanical vibration, shock and condition monitoring — Vocabulary
ISO 2954	Requirements for instruments for measuring vibration severity
ISO 10817-1	Rotating shaft vibration measuring systems — Relative and absolute sensing
ISO 20816-1:2016	Mechanical vibration — Measurement and evaluation — General guidelines

ISO 20816 Series

Standard	Scope	Status
ISO 20816-1:2016	General guidelines	Published
ISO 20816-2:2017	Steam/gas turbines >40 MW, 1500–3600 r/min	Published
ISO 20816-3:2022	Industrial machinery >15 kW, 120–30,000 r/min	Published (this document)
ISO 20816-4:2018	Gas turbine driven sets	Published
ISO 20816-5:2018	Hydraulic power plants	Published
ISO 20816-8:2018	Reciprocating compressor systems	Published
ISO 20816-9	Gear units	In development

Complementary Standards

Standard	Title	Relevance
ISO 21940-11	Rotor balancing — Procedures and tolerances	Balance quality grades G0.4–G4000
ISO 13373-1/2/3	Vibration condition monitoring & diagnostics	FFT, analysis, fault signatures
ISO 18436-2	Vibration analyst certification (Cat I–IV)	Personnel competence
ISO 14694	Industrial fans — Balance quality and vibration	Fan-specific limits

GOST Correspondence (Annex DA)

ISO Standard	Correspondence	GOST Equivalent
ISO 2041	IDT	GOST R ISO 2041-2012
ISO 2954	IDT	GOST ISO 2954-2014
ISO 10817-1	IDT	GOST ISO 10817-1-2002
ISO 20816-1:2016	IDT	GOST R ISO 20816-1-2021

IDT = Identical standards.

Historical Context

ISO 20816-3:2022 replaces ISO 10816-3:2009 (housing vibration) and ISO 7919-3:2009 (shaft vibration), integrating both into a unified evaluation framework. The pioneer work by Rathbone (1939) established the foundation for using velocity as the primary vibration criterion.

16. Frequently Asked Questions

What is the difference between ISO 20816-3 and the old ISO 10816-3?

ISO 20816-3:2022 supersedes and replaces both ISO 10816-3:2009 and ISO 7919-3:2009. Main differences: integration of housing and shaft vibration criteria into one document, updated zone boundaries based on more recent operational experience, clearer guidance on foundation classification, and expanded guidance on low-speed machines. If your specifications reference ISO 10816-3, you should transition to ISO 20816-3.

Should I use velocity or displacement for assessment?

For most machines above 600 r/min, velocity is the primary criterion. Use displacement additionally when: machine speed is ≤600 r/min (displacement may be the limiting factor), significant low-frequency components are present, or measuring shaft relative vibration (always use peak-to-peak displacement). If in doubt, check against both criteria — the worst-case zone governs.

How do I determine if my foundation is rigid or flexible?

The most accurate method is to measure or calculate the lowest natural frequency of the machine-foundation system. Methods: impact test (bump test), operational modal analysis, or FEA calculation. Quick estimate: if the machine visibly moves on its mounts during startup/shutdown, it's likely flexible. If f_n ≥ 1.25 × running frequency → Rigid; otherwise → Flexible. Note: a foundation may be rigid vertically but flexible horizontally.

What if my machine is in Zone C — can I keep running?

Zone C means not suitable for continuous long-term operation, but doesn't require immediate shutdown. You should: investigate the cause, plan remedial action, monitor frequently for rapid changes, set a deadline for repair (next scheduled outage), and ensure vibration doesn't approach Zone D. The decision to continue depends on machine criticality and consequences of failure.

How can balancing help meet ISO 20816-3 limits?

Unbalance is the most common cause of excessive vibration at running speed (1×). Field balancing with the Balanset-1A can reduce vibration from Zone C/D back to Zone A/B. The instrument measures vibration velocity to ISO 20816-3 requirements, calculates correction masses, verifies results, and documents before/after levels for compliance records.

What causes vibration to increase suddenly?

Sudden increases (triggering Criterion II) may indicate: loss of balance weight, bearing damage, coupling failure, structural looseness (foundation bolt loosening), rotor rub, or process changes (cavitation, surge). Any change >25% of B/C boundary warrants investigation, even if absolute level is still acceptable.

What about housing vs shaft disagreement?

If housing vibration indicates Zone B but shaft vibration indicates Zone C, classify the machine as Zone C (the more restrictive assessment governs). There is no simple method to calculate housing vibration from shaft vibration or vice versa. Always use the worst-case zone from dual measurements.

Put it into practice

Related engineering calculators

Browse all 305 free engineering calculators →

Need to measure it for real?

Balanset-1A — portable balancer & vibration analyzer

Two-channel field balancing and vibration diagnostics — used by engineers in 50+ countries. Measure, balance and verify on-site, no disassembly.

€1,975 · in stock Learn more →