Abstract

This report presents a comprehensive analysis of international regulatory requirements for the vibration condition of industrial equipment defined in ISO 10816-1 and its derivative standards. The document reviews the evolution of standardization from ISO 2372 to the current ISO 20816, explains the physical meaning of the measured parameters, and describes the methodology for evaluating the severity of vibration conditions. Special attention is given to the practical implementation of these rules using the portable balancing and diagnostic system Balanset-1A. The report contains a detailed description of the technical characteristics of the instrument, algorithms of its operation in vibrometer and balancing modes, and methodological guidelines for performing measurements to ensure compliance with reliability and safety criteria for rotating machinery.

Chapter 1. Theoretical Foundations of Vibration Diagnostics and Evolution of Standardization

1.1. Physical Nature of Vibration and Selection of Measurement Parameters

Vibration, as a diagnostic parameter, is the most informative indicator of the dynamic condition of a mechanical system. Unlike temperature or pressure, which are integral indicators and often react to faults with a delay, the vibration signal carries information about the forces acting inside the mechanism in real time.

The ISO 10816-1 standard, like its predecessors, is based on measuring vibration velocity. This choice is not accidental and follows from the energetic nature of damage. Vibration velocity is directly proportional to the kinetic energy of the oscillating mass and therefore to the fatigue stresses that arise in machine components.

Vibration diagnostics uses three main parameters, each with its own field of application:

Vibration displacement (Displacement): The oscillation amplitude measured in micrometers (µm). This parameter is critical for low-speed machines (below 600 rpm) and for evaluating clearances in journal bearings, where it is important to prevent rotor-to-stator contact. In the context of ISO 10816-1, displacement has limited use because at high frequencies even small displacements can generate destructive forces.

Vibration velocity (Velocity): The surface point velocity measured in millimeters per second (mm/s). This is the universal parameter for the frequency range from 10 to 1000 Hz, which covers the main mechanical defects: unbalance, misalignment, and looseness. ISO 10816 adopts vibration velocity as the primary assessment criterion. The standard specifies the RMS (root mean square) value, which characterizes the average energy of vibration.

Vibration acceleration (Acceleration): The rate of change of vibration velocity measured in meters per second squared (m/s²) or in g units (1 g = 9.81 m/s²). Acceleration characterizes inertial forces and is most sensitive to high-frequency processes (from 1000 Hz and above), such as early-stage rolling bearing defects, gear mesh problems, and electrical faults in motors.

1.2. Historical Context: From ISO 2372 to ISO 20816

Understanding current requirements requires analyzing their historical development. The evolution of vibration standards spans more than five decades:

This report focuses on ISO 10816-1 and ISO 10816-3, because these documents are the main working tools for about 90% of industrial equipment diagnosed with portable instruments such as Balanset-1A.

Chapter 2. Detailed Analysis of ISO 10816-1 Methodology

2.1. Scope and Limitations

ISO 10816-1 applies to vibration measurements carried out on non-rotating parts of machines (bearing housings, feet, supporting frames). The standard does not apply to vibration caused by acoustic noise and does not cover reciprocating machines (they are covered by ISO 10816-6) which generate specific inertial forces due to their operating principle.

A critical aspect is that the standard regulates in-situ measurements — in real operating conditions, not only on a test stand. This means that the limits account for the influence of the real foundation, piping connections, and operating load conditions.

2.2. Equipment Classification

A key element of the methodology is the division of all machines into classes. Applying Class IV limits to a Class I machine may cause an engineer to miss a dangerous condition, while the opposite may lead to unjustified shutdowns of healthy equipment.

Table 2.1. Machine Classification According to ISO 10816-1

Problem of Identifying Foundation Type (Rigid vs. Flexible)

The standard defines a foundation as rigid if the first natural frequency of the "machine–foundation" system is above the main excitation frequency (rotational frequency). A foundation is flexible if its natural frequency is below the rotational frequency.

In practice this means:

• A machine bolted to a massive concrete shop floor usually belongs to a class with a rigid foundation.
• A machine mounted on vibration isolators (springs, rubber pads) or on a light steel frame (for example, an upper-tier structure) belongs to a class with a flexible foundation.
• The same physical machine can change class if moved from one foundation to another — this is critical to remember when relocating equipment.

2.3. Vibration Evaluation Zones

Instead of a binary "good/bad" evaluation, the standard offers a four-zone scale that supports condition-based maintenance:

2.4. Vibration Limit Values

The table below summarizes the limit values of RMS vibration velocity (mm/s) according to Annex B of ISO 10816-1. These values are empirical and serve as guidelines if the manufacturer's specifications are not available.

Table 2.2. Zone Boundary Values (ISO 10816-1 Annex B)

Visual Comparison: Zone Boundaries by Machine Class

Analytical interpretation. Consider the value 4.5 mm/s. For small machines (Class I) this is the boundary of the emergency condition (C/D), which requires shutdown. For medium-sized machines (Class II) this is the middle of the "requires attention" zone. For large machines on a rigid foundation (Class III) this is only the boundary between "satisfactory" and "unsatisfactory" zones. For machines on a flexible foundation (Class IV) this is a normal operating vibration level (Zone B). This progression demonstrates the risk of using universal limits without proper classification.

2.5. Two Evaluation Criteria: Absolute Value vs. Relative Change

ISO 10816-1 defines two independent evaluation criteria that should be applied simultaneously:

Criterion I — Vibration Magnitude: The absolute broadband RMS vibration velocity compared against the zone limits. This is the primary criterion described in the tables above.

Criterion II — Change in Vibration: A significant change (increase or decrease) in vibration level relative to the established baseline, regardless of whether the absolute level crosses a zone boundary. A sudden change of more than 25% in vibration level may indicate a developing fault even if the machine remains in Zone B. Conversely, a sudden decrease may indicate that a coupling has failed or a component has broken off.

Chapter 3. Complete Overview of the ISO 10816 / 20816 Series

The ISO 10816 standard was published as a multi-part series, where Part 1 provides the general framework and subsequent parts define specific requirements for different machine types. Understanding which part applies to your specific equipment is essential for correct evaluation.

Table 3.0. Full List of ISO 10816 Parts and Their ISO 20816 Replacements

3.1. ISO 7919 Series (Shaft Vibration) — Now Part of ISO 20816

While ISO 10816 focused exclusively on housing vibration, the parallel ISO 7919 series addressed shaft vibration measured using non-contact proximity probes (eddy current sensors). For critical rotating machinery such as large steam turbines, gas turbines, and generators, shaft relative vibration is often the more informative parameter because it directly measures the motion of the rotor within its bearing clearances.

The unification of these two series into ISO 20816 reflects the modern understanding that comprehensive condition monitoring of critical machines requires both housing vibration (for structural assessment) and shaft vibration (for rotor dynamic assessment).

3.2. Related International Standards

ISO 10816 does not exist in isolation. Several companion standards define sensor specifications, balancing quality, and measurement methodology:

3.3. Relationship Between ISO 1940 Balance Quality and ISO 10816 Vibration Zones

One of the most common questions in practice is how the balance quality grade (G value per ISO 1940) relates to the vibration zones in ISO 10816. While no exact mathematical formula links them (the relationship depends on bearing stiffness, machine mass, and support dynamics), there is a general correlation:

• Balance grade G2.5 (typical for fans, pumps, motors) generally achieves Zone A or B on properly installed machines.
• Balance grade G6.3 (general machinery) typically achieves Zone B, but may be in Zone C for rigid, lightweight structures.
• Balance grade G16 (agricultural equipment, crushers) usually corresponds to Zone C or worse per ISO 10816.

The Balanset-1A system can achieve balance quality G2.5 and better, which directly contributes to meeting ISO 10816 Zone A requirements.

Chapter 4. Specifics of Industrial Machines: ISO 10816-3

While ISO 10816-1 defines the general framework, in practice most industrial units (pumps, fans, compressors above 15 kW) are governed by the more specific Part 3 of the standard (ISO 10816-3). It is important to understand the difference because Balanset-1A is often used to balance fans and pumps covered by this part.

4.1. Machine Groups in ISO 10816-3

Unlike the four classes in Part 1, Part 3 divides machines into two main groups:

Group 1: Large machines with rated power above 300 kW, or electrical machines with shaft height greater than 315 mm, operating at speeds between 120 rpm and 15,000 rpm.

Group 2: Medium-sized machines with rated power from 15 kW to 300 kW, or electrical machines with shaft height from 160 mm to 315 mm, at operating speeds between 120 rpm and 15,000 rpm.

4.2. Vibration Limits in ISO 10816-3

The limits depend on foundation type (Rigid / Flexible), which remains the same definition as in Part 1.

Table 4.1. Vibration Limits According to ISO 10816-3 (RMS, mm/s)

Data synthesis. Comparing ISO 10816-1 and ISO 10816-3 tables shows that ISO 10816-3 imposes stricter requirements on medium-power machines (Group 2) on rigid foundations. The boundary of Zone D is set at 4.5 mm/s, which coincides with the limit for Class I in Part 1. This confirms the trend toward stricter limits for modern, faster, and lighter equipment. When using Balanset-1A to diagnose a 45 kW fan on a concrete floor, you should focus on the "Group 2 / Rigid" column of this table, where the transition to the emergency zone occurs at 4.5 mm/s.

4.3. Additional Requirements of ISO 10816-3

ISO 10816-3 adds important provisions beyond the basic zone limits:

• Acceptance testing: For newly installed or repaired machines, vibration should be in Zone A. If it falls in Zone B, an investigation is recommended to determine the cause.
• Operational alarms: The standard recommends setting two alarm levels — ALERT (typically at the B/C boundary) and DANGER (at the C/D boundary). These can be implemented in continuous monitoring systems.
• Transient conditions: The standard acknowledges that during startup and shutdown, vibration may temporarily exceed steady-state limits, particularly when passing through critical speeds (resonances).
• Coupled machines: For coupled equipment (e.g., motor-pump sets), each machine should be evaluated individually using the limits appropriate to its group classification.

Chapter 5. Hardware Architecture of the Balanset-1A System

To implement the requirements of ISO 10816/20816, you need an instrument that provides accurate and repeatable measurements and matches the required frequency ranges. The Balanset-1A system developed by Vibromera is an integrated solution that combines the functions of a two-channel vibration analyzer and a field balancing instrument.

5.1. Measurement Channels and Sensors

The Balanset-1A system has two independent vibration measurement channels (X1 and X2), which allows simultaneous measurements at two points or in two planes.

Sensor type. The system uses accelerometers (vibration transducers that measure acceleration). This is the modern industry standard because accelerometers provide high reliability, wide frequency range, and good linearity.

Signal integration. Because ISO 10816 requires evaluation of vibration velocity (mm/s), the signal from the accelerometers is integrated in hardware or software. This is a critical signal processing step, and the quality of the analog-to-digital converter plays a key role.

Measurement range. The instrument measures vibration velocity (RMS) in the range from 0.05 to 100 mm/s. This range fully covers all ISO 10816 evaluation zones (from Zone A < 0.71 to Zone D > 45 mm/s for the largest machines).

5.2. Frequency Characteristics and Accuracy

The metrological characteristics of Balanset-1A fully comply with the requirements of the standard.

Frequency range. The basic version of the instrument operates in the 5 Hz – 550 Hz band. The lower limit of 5 Hz (300 rpm) even exceeds the standard ISO 10816 requirement of 10 Hz and supports diagnostics of low-speed machines. The upper limit of 550 Hz covers up to the 11th harmonic for machines with a rotational frequency of 3000 rpm (50 Hz), which is sufficient to detect unbalance (1×), misalignment (2×, 3×), and looseness. Optionally, the frequency range can be extended to 1000 Hz, fully covering all standard requirements.

Amplitude accuracy. The amplitude measurement error is ±5% of full scale. For operational monitoring tasks, where zone boundaries differ by hundreds of percent, this accuracy is more than sufficient.

Phase accuracy. The instrument measures phase angle with an accuracy of ±1 degree. Although phase is not regulated by ISO 10816, it is critically important for the balancing procedure.

5.3. Tachometer Channel

The kit includes a laser tachometer (optical sensor) that performs two functions: measures rotor speed (RPM) from 150 to 60,000 rpm (in some versions up to 100,000 rpm), making it possible to identify whether vibration is synchronous with rotational frequency (1×) or asynchronous; and generates a reference phase signal (phase mark) for synchronous averaging and calculating correction mass angles during balancing.

5.4. Connections and Layout

The standard kit includes sensor cables 4 meters long (optional 10 meters). This increases safety during in-situ measurements. Long cables let the operator stay at a safe distance from rotating machine parts, which meets industrial safety requirements for working with rotating equipment.

Table 5.1. Balanset-1A Key Specifications vs. ISO 10816 Requirements

Chapter 6. Measurement Methodology and ISO 10816 Evaluation Using Balanset-1A

6.1. Preparation for Measurements

Identify the machine. Determine the machine class or group (according to Chapters 2 and 4 of this report). For example, a "45 kW fan on vibration isolators" belongs to Group 2 (ISO 10816-3) with a flexible foundation.

Software installation. Install Balanset-1A drivers and software from the supplied USB drive. Connect the interface unit to the laptop's USB port.

Mount the sensors. Install sensors on bearing housings — not on thin covers, guards, or sheet metal casings. Use magnetic bases and ensure the magnet sits firmly on a clean, flat surface. Paint or rust under the magnet acts as a damper and reduces high-frequency readings. Maintain orthogonality: perform measurements in vertical (V), horizontal (H), and axial (A) directions at each bearing. Balanset-1A has two channels, so you can measure V and H simultaneously at one support.

6.2. Vibrometer Mode (F5)

Balanset-1A software has a dedicated mode for ISO 10816 evaluation. Run the program, press F5 (or click the "F5 - Vibrometer" button in the interface), then press F9 (Run) to start data acquisition.

Indicator analysis:

• RMS (Total): The instrument displays overall RMS vibration velocity (V1s, V2s). This is the value you compare with the standard's tabulated limits.
• 1× Vibration: The instrument extracts the vibration amplitude at rotational frequency (synchronous component).

If the RMS value is high (Zone C/D) but the 1× component is low, the problem is not unbalance. It may be a bearing fault, cavitation (for a pump), or electromagnetic issues. If RMS is close to the 1× value (for example, RMS = 10 mm/s, 1× = 9.8 mm/s), unbalance dominates and balancing will reduce vibration by approximately 95%.

6.3. Spectral Analysis (FFT)

If overall vibration exceeds the limit (Zone C or D), you must identify the cause. The F5 mode includes a Charts tab with FFT spectrum display.

• A dominant peak at 1× (rotational frequency) indicates unbalance.
• Peaks at 2×, 3× indicate misalignment or looseness.
• High-frequency "noise" or a forest of harmonics indicates rolling bearing defects.
• The blade passing frequency (number of blades × rpm) indicates aerodynamic problems in a fan or hydraulic problems in a pump.
• 2× line frequency (100 Hz or 120 Hz) indicates electrical faults in motors (stator eccentricity, broken rotor bars).

Balanset-1A provides these visualizations, which turns it from a simple "compliance meter" into a full diagnostic tool.

6.4. Measurement Points and Directions

ISO 10816-1 recommends measuring vibration in three mutually perpendicular directions at each bearing location. For a typical two-bearing machine, this means up to six measurement points (3 directions × 2 bearings). In practice, the most important measurements are:

• Vertical (V): Most sensitive to unbalance. Typically gives the highest readings because bearings have less stiffness in the vertical direction.
• Horizontal (H): Sensitive to misalignment and looseness. Horizontal vibration that significantly exceeds vertical vibration often indicates a soft foot or loose bolts.
• Axial (A): Elevated axial vibration (more than 50% of radial vibration) suggests misalignment, bent shaft, or unbalanced overhung rotor.

The highest reading among all measurement points and directions is typically used for the ISO 10816 evaluation. Always record all measurements for trend analysis.

Chapter 7. Balancing as a Correction Method: Practical Use of Balanset-1A

When diagnostics (based on 1× dominance in the spectrum) indicate unbalance as the main cause of ISO 10816 limit exceedance, the next step is balancing. Balanset-1A implements the influence coefficient method (three-run method).

7.1. Balancing Theory

Unbalance occurs when the rotor's center of mass does not coincide with its axis of rotation. This causes a centrifugal force F = m · r · ω² that generates vibration at rotational frequency. The goal of balancing is to add a correction mass (weight) that produces a force equal in magnitude and opposite in direction to the unbalance force.

7.2. Single-Plane Balancing Procedure

Use this procedure for narrow rotors (fans, pulleys, disks). Select F2 mode in the program.

Run 0 — Initial: Start the rotor, press F9. The instrument measures the initial vibration (amplitude and phase). Example: 8.5 mm/s at 120°.

Run 1 — Trial Weight: Stop the rotor, mount a trial weight of known mass (for example, 10 g) at an arbitrary location. Start the rotor, press F9. Example: 5.2 mm/s at 160°.

Calculation and correction: The program automatically calculates the mass and angle of the correction weight. For example, the instrument may instruct: "Add 15 g at an angle of 45° from the trial weight position." Balanset functions support split weights: if you cannot place the weight at the calculated location, the program splits it into two weights for mounting, for example, on fan blades.

Run 2 — Verification: Install the calculated correction weight (removing the trial weight if required). Start the rotor and confirm that residual vibration has dropped to Zone A or B according to ISO 10816 (for example, below 2.8 mm/s for Group 2 / Rigid).

7.3. Two-Plane Balancing

Long rotors (shafts, crusher drums) require dynamic balancing in two correction planes. The procedure is similar but requires two vibration sensors (X1, X2) and three runs (Initial, Trial weight in Plane 1, Trial weight in Plane 2). Use F3 mode for this procedure.

Chapter 8. Practical Scenarios and Interpretation (Case Studies)

Chapter 9. Relationship Between Vibration Parameters: Displacement, Velocity, Acceleration

Understanding the mathematical relationship between the three vibration parameters is important for converting between them and for understanding why ISO 10816 chose velocity as its primary metric.

For a simple harmonic motion at frequency f (Hz):

• Displacement: D = D₀ · sin(2πft), measured in µm (peak or peak-to-peak)
• Velocity: V = 2πf · D₀ · cos(2πft), measured in mm/s
• Acceleration: A = (2πf)² · D₀ · sin(2πft), measured in m/s²

The key relationships (for peak values at frequency f):

• V_peak (mm/s) = π · f · D_p-p (µm) / 1000
• A_peak (m/s²) = 2πf · V_peak (mm/s) / 1000

This explains why displacement is dominant at low frequencies and acceleration is dominant at high frequencies, while velocity provides a relatively flat (frequency-independent) representation of vibration severity across the typical machine speed range. A constant velocity value represents constant stress in the structure regardless of frequency — this is the fundamental reason ISO 10816 uses velocity.

Table 9.1. Practical Conversion Examples at 50 Hz (3000 rpm)

Chapter 10. Common Measurement Errors and How to Avoid Them

Even with a properly calibrated instrument like the Balanset-1A, measurement errors can lead to incorrect conclusions. Here are the most common pitfalls:

10.1. Sensor Mounting Errors

Problem: Sensor mounted on a guard, thin cover, or loose structure instead of the bearing housing. This causes false high readings due to structural resonances of the cover, leading to unnecessary shutdowns.

Solution: Always mount directly on the bearing housing. Use magnetic mounting on a clean, flat, metallic surface. For surfaces with paint thicker than 0.1 mm, scrape a small area to bare metal.

10.2. Wrong Machine Classification

Problem: Applying Class I limits to a 200 kW compressor (which should be Group 2 per ISO 10816-3) results in premature alarms.

Solution: Always identify the machine's power rating, speed, and foundation type before selecting the applicable standard and group.

10.3. Ignoring Operating Conditions

Problem: Measuring vibration during startup or at partial load. ISO 10816 limits apply to steady-state operation at normal operating conditions.

Solution: Allow the machine to reach thermal equilibrium and normal operating speed/load before recording measurements. For electric motors, this typically means at least 15 minutes of operation.

10.4. Cable and Electrical Noise

Problem: Running sensor cables alongside power cables introduces electromagnetic interference, causing artificially elevated readings especially at 50/60 Hz and harmonics.

Solution: Route sensor cables away from power cables. Use shielded cables where possible. The Balanset-1A cables are shielded by design, but proper routing remains important.

10.5. Single-Point Measurements

Problem: Measuring only one direction at one bearing and concluding "the machine is fine."

Solution: Measure in at least two directions (V and H) at each bearing. Use the highest reading for the ISO 10816 evaluation. Significant differences between directions can indicate specific faults (e.g., horizontal > vertical often indicates structural looseness).

Frequently Asked Questions (FAQ)

Conclusion

ISO 10816-1 and its specialized Part 3 provide a fundamental basis for ensuring industrial equipment reliability. The transition from subjective perception to quantitative assessment of vibration velocity (RMS, mm/s) lets engineers objectively classify machine condition and plan maintenance based on actual data rather than arbitrary schedules.

The four-zone evaluation system (A through D) provides a universally understood language for communicating machine condition between maintenance teams, management, and equipment vendors. When combined with spectral analysis, this methodology enables not just detection of problems but also identification of root causes — unbalance, misalignment, bearing wear, looseness, and electrical faults.

Instrumental implementation of these standards using the Balanset-1A system has proven effective. The instrument provides metrologically accurate measurements in the 5–550 Hz range (fully covering standard requirements for most machines) and offers the functionality required to identify the causes of elevated vibration (spectral analysis) and eliminate them (balancing).

For operating companies, implementing regular monitoring based on the ISO 10816 methodology and instruments such as Balanset-1A is a direct investment in reducing operating costs. The ability to distinguish Zone B from Zone C helps avoid both premature repairs of healthy machines and catastrophic failures caused by ignoring critical vibration levels.

End of report