What Is ISO 20816-1?

ISO 20816-1:2016 (full title: "Mechanical vibration — Measurement and evaluation of machine vibration — Part 1: General guidelines") is the current international standard providing the framework for how machinery vibration should be measured and evaluated. It was published in 2016 and replaces two older foundational standards that had been in use since the 1990s.

The most significant change is the unification of two previously separate measurement philosophies into a single, cohesive document:

• ISO 10816-1 — covered vibration measured on non-rotating parts (bearing housings, machine casing) using seismic sensors (accelerometers).
• ISO 7919-1 — covered vibration measured on rotating shafts using non-contact proximity probes.

ISO 20816-1 combines both approaches into one framework, recognizing that comprehensive machine assessment often requires both types of measurement. A machine might have acceptable casing vibration but dangerous shaft movement (indicating a rotor-dynamic problem), or vice versa (indicating a structural/foundation issue). Only by evaluating both can you get the full picture.

What the Standard Covers

1. Scope and measurement types — defines both casing and shaft vibration measurement methodologies
2. Instrumentation requirements — sensor types, frequency ranges, calibration, mounting standards
3. Evaluation criteria — the two-criterion approach (absolute limits + change from baseline)
4. Evaluation zones — the four-zone classification system (A, B, C, D)
5. Combined assessment and acceptance — how to use both measurement types together, acceptance testing vs. operational monitoring

The Complete ISO 20816 Series

ISO 20816 is a multi-part standard. Part 1 provides the general framework; other parts provide specific numerical limits for different machine categories.

Measurement Types

ISO 20816-1 formally unifies two fundamentally different measurement approaches. Understanding the distinction is critical for correct application.

Casing Vibration (Non-Rotating Parts)

• What: Vibration of the stationary machine structure — bearing housings, pedestals, frames, casing.
• Sensor: Seismic transducers — piezoelectric accelerometers (most common) or velocity transducers — mounted on the bearing housing per ISO 5348.
• Parameter: Broadband RMS velocity in mm/s (or in/s in some regions).
• Frequency range: 10–1000 Hz standard; 2–1000 Hz for low-speed machines (<120 RPM).
• What it tells you: The vibration energy being transmitted into the machine structure. Reflects the forces acting on bearings and the structural response. Directly correlates with bearing fatigue and structural damage risk.
• Equipment: The Balanset-1A measures broadband RMS velocity in its Vibrometer mode (F5), making it directly suitable for ISO 20816 casing assessment.

Shaft Vibration (Rotating Parts)

• What: Dynamic displacement of the shaft relative to the bearing housing — how much the shaft actually moves within its bearing clearance.
• Sensor: Non-contact eddy-current proximity probes, typically installed in orthogonal pairs (X-Y) at each bearing per API 670.
• Parameter: Peak-to-peak displacement in μm (micrometers) or mils (1 mil = 25.4 μm).
• Frequency range: Primarily shaft synchronous (1×) and sub-synchronous components.
• What it tells you: The actual rotor dynamic behavior — orbit shape, whirl direction, rub contact. Critical for detecting shaft bow, oil whirl, seal contact, and misalignment that may not transfer efficiently to the casing.
• Equipment: Permanently installed proximity probes (not typically portable instruments). Primarily used on large turbo-machinery with fluid-film (journal) bearings.

Instrumentation Requirements

The standard specifies that the entire measurement chain — transducer, cabling, signal conditioning, and analyzer — must be calibrated and capable of accurately measuring over the required frequency range. Key references:

• Accelerometer mounting: Per ISO 5348 — stud mount preferred, magnetic acceptable for routine monitoring, adhesive for permanent installation.
• Proximity probe installation: Per API 670 — probe gap, target surface finish, orthogonal pair orientation, and cable routing requirements.
• Calibration: Regular calibration of the entire chain against traceable standards. The Balanset-1A ships factory-calibrated and can be verified against known vibration sources.

Evaluation Zones A, B, C, D

The four-zone system is the most recognized feature of the ISO vibration standards. It provides a universal, color-coded framework for classifying vibration severity and determining appropriate action.

Zone Boundary Values — Casing Vibration (ISO 20816-3)

These are the specific numerical limits for broadband RMS velocity on bearing housings, applicable to industrial machines with power above 15 kW and speeds from 120 to 15,000 RPM. These values were originally established in ISO 10816-3 and are carried forward with minor updates in ISO 20816-3:2022.

Zone Boundary Values — Shaft Displacement (ISO 20816-2)

For turbo-machinery with proximity probes, shaft displacement limits are speed-dependent. The standard uses a formula based on the square root of speed ratio.

The Two Evaluation Criteria

ISO 20816-1 mandates that vibration assessment must consider both criteria simultaneously. Using only one gives an incomplete picture.

Criterion 1 — Absolute Magnitude

Compare the measured vibration value against the fixed zone boundaries from the applicable part of ISO 20816. This tells you the machine's condition relative to the general population of similar machines.

• Use for: Acceptance testing of new/repaired machines, baseline assessment, setting trip alarms, comparing machines across a fleet.
• Limitation: A machine that has always been at 4.0 mm/s (Zone B for Group 1) might be perfectly healthy — that's its normal operating level. Criterion 1 alone doesn't tell you if something has changed.

Criterion 2 — Change from Baseline

Compare the current vibration to an established reference (baseline) value. The baseline is typically measured after commissioning, after maintenance, or as a statistical average over a stable operating period.

• Use for: Trend-based predictive maintenance, early fault detection, detecting deterioration regardless of absolute level.
• Key insight: A significant change in vibration — even if the absolute value is still in Zone A or B — is often the earliest and most reliable indicator of a developing fault.

Machine Groups (ISO 20816-3)

ISO 20816-3 (and its predecessor ISO 10816-3) classifies machines into four groups based on power rating and foundation type. The zone boundaries are different for each group because larger machines on flexible foundations naturally have higher vibration than small machines on rigid foundations.

Alarm and Trip Setpoints

The practical application of ISO 20816 in monitoring systems requires setting Alert (alarm) and Danger (trip) setpoints. The standard provides guidance for both absolute and relative setpoints.

Absolute Setpoints (from Criterion 1)

• Alert = B/C zone boundary value. When vibration exceeds this, increase monitoring, investigate root cause, plan corrective action.
• Trip = C/D zone boundary value. When vibration exceeds this, automatic shutdown (if available) or immediate manual action to prevent damage.

Relative Setpoints (from Criterion 2)

• Relative Alert = Baseline × multiplier (typically 2.0–2.5×). A doubling or more of vibration from baseline indicates a developing fault.
• The effective alert setpoint should be whichever is lower between the absolute alert and the relative alert. This ensures the first criterion to be violated triggers the alarm.

Acceptance Testing vs. Operational Monitoring

ISO 20816-1 clearly distinguishes between two assessment contexts:

Acceptance Testing

Used when commissioning new machines or accepting machines after overhaul. The requirement is typically that vibration falls within Zone A or Zone B. This is a strict pass/fail criterion — a new machine delivered in Zone C would normally be rejected.

• Measurement conditions must be tightly controlled (stable speed, full load, thermal equilibrium).
• Multiple readings at each measurement point.
• Results documented in a formal acceptance report.

Operational Monitoring

Used for ongoing condition assessment of in-service machines. The focus shifts from pass/fail to trending and change detection (Criterion 2). Alert and trip setpoints are the primary tools.

• Portable route-based data collection (Balanset-1A) or permanent online monitoring.
• Consistent measurement points, conditions, and procedures for valid trend comparison.
• Action decisions based on both absolute zone and trend direction.

Migration from ISO 10816 to ISO 20816

Many facilities still reference ISO 10816 in their procedures, monitoring databases, and specifications. Here's what you need to know about the transition.

Practical Application with Balanset-1A

The Balanset-1A portable vibration analyzer directly supports ISO 20816 casing vibration assessment through its built-in measurement modes.

Vibrometer Mode (F5)

Measures broadband RMS velocity — the exact parameter specified by ISO 20816 for casing vibration. Display shows:

• V1s (overall vibration) — compare directly with zone boundaries
• V1o (1× RPM component) — indicates how much of the total vibration is from unbalance
• Both channels simultaneously — near and far bearing in one measurement

Spectrum Analyzer (F1 / F8)

Displays the FFT frequency spectrum, allowing you to identify the source of high vibration (unbalance at 1×, misalignment at 2×, bearing defects at characteristic frequencies). See the Vibration Analysis Guide for spectrum interpretation.

Balancing Mode

If vibration is diagnosed as unbalance (dominant 1× RPM peak), the Balanset-1A can immediately proceed to field balancing to correct it — reducing vibration from Zone C or D back to Zone A or B. See the Field Dynamic Balancing Guide for the complete procedure.

Frequently Asked Questions

What is the difference between ISO 20816 and ISO 10816?

ISO 20816 replaces ISO 10816 by combining casing vibration (formerly ISO 10816) and shaft vibration (formerly ISO 7919) into a unified standard. The zone boundary values for casing vibration in ISO 20816-3 are very similar to those in ISO 10816-3. The main improvement is the integration of both measurement philosophies in one document.

Is ISO 10816 still valid?

ISO 10816 parts have been formally withdrawn as they are superseded by corresponding ISO 20816 parts. However, the vibration limits are widely embedded in existing monitoring systems and contracts. The numerical values for casing vibration are essentially unchanged, so existing ISO 10816-based programs remain technically valid in practice.

Which parameter should I measure — velocity or displacement?

For general industrial machines with rolling-element bearings measured externally (portable instruments): RMS velocity in mm/s. For large turbo-machinery with journal bearings and installed proximity probes: peak-to-peak shaft displacement in μm. If both are available, evaluate both — they provide complementary information.

How do I determine the machine group?

Two factors: power rating (above or below 300 kW) and foundation type (rigid or flexible). A 75 kW motor bolted to a concrete pad = Group 2. A 500 kW compressor on a steel platform = Group 3. See the Machine Groups section above.

Can a machine in Zone B still have a developing fault?

Yes — this is exactly why Criterion 2 exists. If a machine's baseline was 0.8 mm/s and it rises to 2.2 mm/s, it's still in Zone B for Group 2 (below 2.8 mm/s), but the 2.75× increase from baseline indicates a significant developing problem.

What vibration level should I target after balancing?

After field balancing, aim for Zone A (below the A/B boundary for your machine group). For a Group 2 machine, this means below 1.4 mm/s. The Balancing Guide covers the procedure in detail.

What frequency range does the broadband RMS velocity cover?

Standard range is 10–1000 Hz per ISO 20816-1. This captures the most common fault signatures: 1× to ~60× for a machine running at 1000 RPM (~17 Hz), or 1× to ~20× for a machine at 3000 RPM (50 Hz). Low-speed machines (<120 RPM) use an extended range of 2–1000 Hz.

Do I need to buy the ISO 20816-1 document to use the zone values?

ISO 20816-1 itself does not contain specific zone values — it only defines the methodology. The zone boundary numbers are in ISO 20816-3 (for general industrial machines). For the complete official documents with all procedures and annexes, purchase from ISO Store. The zone values published in this guide are from publicly available references and widely used in industry.

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