Comprehensive Analysis of ISO 20816-3: Measurement, Evaluation, and Instrumental Implementation via the Balanset-1A System

Sažetak

The industrial landscape has witnessed a significant paradigm shift in the standardization of machinery health monitoring. The introduction of ISO 20816-3:2022 represents a consolidation and modernization of previous methodologies, specifically merging the evaluation of housing vibration (formerly ISO 10816-3) and rotating shaft vibration (formerly ISO 7919-3) into a single, cohesive framework. This report provides an exhaustive analysis of ISO 20816-3, dissecting its chapters, normative annexes, and physical principles. Furthermore, it integrates a detailed technical evaluation of the Balanset-1A portable vibration analyzer and balancer, demonstrating how this specific instrument facilitates compliance with the rigorous demands of the standard. Through a synthesis of signal processing theory, mechanical engineering principles, and practical operational procedures, this document serves as a definitive guide for reliability engineers seeking to align their condition monitoring strategies with global best practices using accessible, high-precision instrumentation.

Part I: The Theoretical Framework of ISO 20816-3

1.1 Evolution of Vibration Standards: The Convergence of ISO 10816 and ISO 7919

The history of vibration standardization is characterized by a gradual movement from fragmented, component-specific guidelines toward holistic machine evaluation. Historically, the assessment of industrial machinery was bifurcated. The ISO 10816 series focused on the measurement of non-rotating parts—specifically, the bearing housings and pedestals—using accelerometers or velocity transducers. Conversely, the ISO 7919 series addressed the vibration of rotating shafts relative to their bearings, primarily utilizing non-contact eddy current probes.

This separation often led to diagnostic ambiguity. A machine might exhibit acceptable housing vibration (Zone A according to ISO 10816) while simultaneously suffering from dangerous shaft runout or instability (Zone C/D according to ISO 7919), particularly in scenarios involving heavy casings or fluid-film bearings where the transmission path of vibration energy is attenuated. ISO 20816-3 resolves this dichotomy by superseding both ISO 10816-3:2009 and ISO 7919-3:2009.1 By integrating these perspectives, the new standard acknowledges that the vibrational energy generated by rotor-dynamic forces manifests differently across the machine structure depending on stiffness, mass, and damping ratios. Consequently, a compliant evaluation now requires a dual perspective: assessing both the absolute vibration of the structure and, where applicable, the relative motion of the shaft.

The Balanset-1A system enters this landscape as a tool designed to bridge these measurement domains. Its architecture, which supports both piezoelectric accelerometers for housing measurements and direct voltage inputs for linear displacement sensors, mirrors the dual-nature philosophy of the ISO 20816 series.3 This convergence simplifies the technician’s toolkit, allowing a single instrument to perform the comprehensive assessments now mandated by the unified standard.

1.2 Scope and Applicability: Defining the Industrial Machinery Landscape

Chapter 1 of ISO 20816-3 meticulously defines the boundaries of its application. The standard is not a catch-all; it is specifically calibrated for industrial machines with a power rating above 15 kW and operating speeds between 120 r/min and 30,000 r/min.1 This wide operational envelope covers the vast majority of critical assets in the manufacturing, power generation, and petrochemical sectors.

The equipment specifically covered includes:

• Steam Turbines and Generators: Units with outputs less than or equal to 40 MW are covered here. Larger units (above 40 MW) typically fall under ISO 20816-2, unless they operate at speeds other than the synchronous grid frequencies (1500, 1800, 3000, or 3600 r/min).6
• Rotary Compressors: Including both centrifugal and axial designs used in process industries.
• Industrial Gas Turbines: Specifically those with outputs of 3 MW or less. Larger gas turbines are segregated into separate parts of the standard due to their unique thermal and dynamic characteristics.1
• Pumpe: Centrifugal pumps driven by electric motors are a core constituent of this group.
• Elektromotori: Motors of any type are included, provided they are coupled flexibly. Rigidly coupled motors are often assessed as part of the driven machine system or under specific sub-clauses.
• Fans and Blowers: Critical for HVAC and industrial process air handling.6

Exclusions: It is equally important to understand what is excluded. Machines with reciprocating masses (like piston compressors) generate vibration profiles dominated by impacts and varying torques, requiring the specialized analysis found in ISO 20816-8. Similarly, wind turbines, which operate under highly variable aerodynamic loads, are covered by ISO 10816-21.7 The Balanset-1A’s specific design features, such as its rotation speed measurement range of 150 to 60,000 rpm 8, align perfectly with the standard’s 120–30,000 rpm scope, ensuring that the instrument is capable of monitoring the full spectrum of applicable machinery.

1.3 Machine Classification Systems: The Physics of Support Stiffness

A critical innovation retained from previous standards is the classification of machinery based on support stiffness. ISO 20816-3 divides machines into groups not just by size, but by dynamic behavior.

1.3.1 Group Classification by Power and Size

The standard categorizes machines into two primary groups to apply appropriate severity limits:

• Grupa 1: Large machinery with a rated power above 300 kW, or electrical machines with a shaft height exceeding 315 mm. These machines typically possess massive rotors and generate significant dynamic forces.9
• Grupa 2: Medium-sized machinery with a rated power between 15 kW and 300 kW, or electrical machines with shaft heights between 160 mm and 315 mm.10

1.3.2 Support Flexibility: Rigid vs. Flexible

The distinction between “rigid” and “flexible” supports is a matter of physics, not just construction material. A support is considered rigid in a specific measurement direction if the first natural frequency (resonance) of the combined machine-support system is significantly higher than the main excitation frequency (typically the rotational speed). Specifically, the natural frequency should be at least 25% higher than the operating speed. In contrast, flexible supports have natural frequencies that may be near or below the operating speed, leading to resonance amplification or isolation effects.10

This distinction is crucial because flexible supports naturally allow higher vibration amplitudes for the same amount of internal exciting force (unbalance). Therefore, the allowable vibration limits for flexible supports are generally higher than for rigid supports. The Balanset-1A facilitates the determination of support characteristics through its phase measurement capabilities. By performing a run-up or coast-down test (using the “RunDown” chart feature mentioned in software specs 11), an analyst can identify resonant peaks. If a peak occurs within the operating range, the support is dynamically flexible; if the response is flat and linear up to the operating speed, it is rigid. This diagnostic capability allows the user to select the correct evaluation table in ISO 20816-3, preventing false alarms or missed faults.

Part II: Measurement Methodology and Physics

Chapter 4 of ISO 20816-3 lays out the rigorous procedural requirements for data acquisition. The validity of any evaluation depends entirely on the fidelity of the measurement.

2.1 Instrumentation Physics: Transducer Selection and Response

The standard mandates the use of instrumentation capable of measuring broad-band root-mean-square (r.m.s.) vibration velocity. The frequency response must be flat over a range of at least 10 Hz to 1,000 Hz for general machinery.12 For lower-speed machines (operating below 600 r/min), the lower limit of the frequency response must extend down to 2 Hz to capture the fundamental rotational components.

The Balanset-1A Technical Compliance:
The Balanset-1A vibration analyzer is engineered with these specific requirements in mind. Its specifications list a vibration frequency range of 5 Hz to 550 Hz for standard operations, with options to extend measurement capabilities.8 The 5 Hz lower limit is critical; it ensures compliance for machines running as slow as 300 rpm, covering the vast majority of industrial applications. The upper limit of 550 Hz covers the critical harmonics (1x, 2x, 3x, etc.) and blade pass frequencies for most standard pumps and fans. Furthermore, the device’s accuracy is rated at 5% of full scale, satisfying the metrological rigor expected by ISO 2954 (Requirements for instruments for measuring vibration severity).8

The standard distinguishes between two primary measurement types, both supported by the Balanset-1A ecosystem:

• Seismic Transducers (Accelerometers): These measure absolute housing vibration. They are sensitive to force transmission through the bearing pedestal. The Balanset-1A kit includes two single-axis accelerometers (typically ADXL series based technology or piezoelectric) with magnetic mounts.14
• Non-contacting Transducers (Proximity Probes): These measure relative shaft displacement. They are essential for fluid-film bearing machines where the shaft moves within the clearance.

2.2 Deep Dive: Relative Shaft Vibration and Sensor Integration

While ISO 20816-3 focuses heavily on housing vibration, Annex B explicitly deals with shaft relative vibration. This requires the use of eddy current probes (proximity probes). These sensors operate by generating a radio frequency (RF) field that induces eddy currents in the conductive shaft surface. The impedance of the probe coil changes with the gap distance, producing a voltage output proportional to displacement.15

Integrating Eddy Current Probes with Balanset-1A:
A unique feature of the Balanset-1A is its adaptability to these sensors. While primarily supplied with accelerometers, the device’s inputs can be configured for “Linear” mode to accept voltage signals from third-party proximity probe drivers (proximitors).3

• Voltage Input: Most industrial proximity probes output a negative DC voltage (e.g., -24V supply, 200 mV/mil scale). The Balanset-1A allows users to input custom sensitivity coefficients (e.g., mV/µm) in the “Settings” window (F4 key).3
• DC Offset Removal: Proximity probes carry a large DC gap voltage (bias) with a small AC vibration signal riding on top. The Balanset-1A software includes a “Remove DC” function to filter out the gap voltage, isolating the dynamic vibration signal for analysis against ISO 20816-3 limits.3
• Linearity and Calibration: The software allows the user to define calibration factors (e.g., Kprl1 = 0.94 mV/µm) ensuring that the reading on the laptop screen corresponds exactly to the physical displacement of the shaft.3 This capability is indispensable when applying the criteria of Annex B, which are specified in micrometers of displacement rather than millimeters per second of velocity.

2.3 The Physics of Mounting: Ensuring Data Fidelity

ISO 20816-3 emphasizes that the method of sensor mounting must not degrade the accuracy of the measurement. The resonant frequency of the mounted sensor must be significantly higher than the frequency range of interest.

• Stud Mounting: The gold standard, offering the highest frequency response (up to 10 kHz+).
• Magnetic Mounting: A practical compromise for portable data collection.

The Balanset-1A utilizes a magnetic mounting system with a 60 kgf (kilogram-force) holding strength.17 This high clamping force is critical. A weak magnet introduces a “bouncing” effect or a mechanical low-pass filter, severely attenuating high-frequency signals. With 60 kgf, the contact stiffness is sufficient to push the mounted resonance well above the 1000 Hz range of interest for ISO 20816-3, ensuring that the data collected is a true representation of machine behavior and not an artifact of the attachment method.12

2.4 Signal Processing: RMS vs. Peak

The standard specifies the use of Root Mean Square (RMS) velocity for non-rotating parts. The RMS value is a measure of the total energy contained in the vibration signal and is directly related to the fatigue stress imposed on machine components.

Equation for RMS:

V_rms = √((1/T) ∫₀^T v²(t) dt)

For shaft vibration (Annex B), the standard uses peak-to-peak displacement (S_str.), which represents the total physical excursion of the shaft within the bearing clearance.

S_str. = S_max − S_min

Balanset-1A Processing:
The Balanset-1A performs these mathematical transformations internally. The ADC (Analog-to-Digital Converter) samples the raw signal, and the software computes the RMS velocity for housing measurements and peak-to-peak displacement for shaft measurements. Crucially, it calculates the broadband value (Overall), which sums the energy across the entire frequency spectrum (e.g., 10-1000 Hz). This “Overall” value is the primary number used to categorize the machine into Zones A, B, C, or D. Additionally, the device provides FFT (Fast Fourier Transform) capabilities, allowing the analyst to see the individual frequency components (1x, 2x, harmonics) that make up the overall RMS value, aiding in the diagnosis of the source of the vibration.8

2.5 Background Vibration: The Signal-to-Noise Challenge

A critical, often overlooked aspect of ISO 20816-3 is the handling of background vibration—vibration transmitted to the machine from external sources (e.g., adjacent machines, floor vibration) when the machine is stopped.

The Rule: If the background vibration exceeds 25% of the vibration measured when the machine is running, or 25% of the boundary between Zone B and C, severe corrections are required, or the measurement may be considered invalid.18 Previous versions of standards often cited a “one-third” rule, but ISO 20816-3 tightens this logic.

Procedural Implementation with Balanset-1A:

1. The technician places the Balanset-1A sensors on the machine while it is stopped.
2. Using the “Vibrometer” mode (F5 key), the background RMS level is recorded.13
3. The machine is started and brought to load. The operational RMS is recorded.
4. A comparison is made. If the operational level is 4.0 mm/s and the background was 1.5 mm/s (37.5%), the background is too high. The Balanset-1A’s ability to perform spectral subtraction (viewing the spectrum of the background vs. the running machine) helps identify if the background is at a specific frequency (e.g., 50 Hz from a nearby compressor) that can be ignored or filtered out mentally by the analyst.

Part III: Evaluation Criteria – The Heart of the Standard

Chapter 6 constitutes the core of ISO 20816-3, providing the decision logic for machine acceptability.

3.1 Criterion I: Vibration Magnitude and Zoning

The standard evaluates the severity of vibration based on the maximum magnitude observed at the bearing housings. To facilitate decision-making, it defines four evaluation zones:

• Zona A: Vibration of newly commissioned machines. This is the “Gold Standard.” A machine in this zone is in pristine mechanical condition.
• Zona B: Machines considered acceptable for unrestricted long-term operation. This is the typical “Green” operating range.
• Zona C: Machines considered unsatisfactory for long-term continuous operation. Generally, the machine may be operated for a limited period until a suitable opportunity for remedial action (maintenance) arises. This is the “Yellow” or “Alarm” state.
• Zona D: Vibration values in this zone are normally considered to be of sufficient severity to cause damage to the machine. This is the “Red” or “Trip” state.5

Table 1: Simplified ISO 20816-3 Zone Limits (Velocity RMS, mm/s) for Group 1 and 2

Grupa strojeva	Vrsta temelja	Zone A/B Boundary	Zone B/C Boundary	Zone C/D Boundary
Group 1 (>300 kW)	Kruto	2.3	4.5	7.1
	Fleksibilan	3.5	7.1	11.0
Group 2 (15-300 kW)	Kruto	1.4	2.8	4.5
	Fleksibilan	2.3	4.5	7.1

Note: These values are derived from Annex A of the standard and represent general guidelines. Specific machine types may have different limits.

Balanset-1A Implementation:
The Balanset-1A software does not just display a number; it contextually aids the user. While the user must select the class, the software’s “Reports” function allows for the documentation of these values against the standard. When a technician measures a 5.0 mm/s vibration on a 50 kW pump (Group 2) on a rigid foundation, the Balanset-1A reading clearly exceeds the Zone C/D boundary (4.5 mm/s), indicating an immediate need for shutdown and repair.

3.2 Criterion II: Change in Vibration Magnitude

Perhaps the most significant advancement in the 20816 series is the formalized emphasis on the change in vibration, independent of absolute limits.

The 25% Rule: ISO 20816-3 states that a change in vibration magnitude of greater than 25% of the Zone B/C boundary (or 25% of the previous steady-state value) should be considered significant, even if the absolute value remains within Zone A or B.20

Implications:
Consider a fan operating steadily at 2.0 mm/s (Zone B). If the vibration suddenly jumps to 2.8 mm/s, it is still technically in Zone B (for some classes) or just entering Zone C. However, this is a 40% increase. Such a sudden shift often indicates a specific failure mode: a cracked rotor component, a shifted balance weight, or a thermal rub. Ignoring this because “it’s still in the green” is a recipe for catastrophic failure.

Balanset-1A Trend Analysis:
The Balanset-1A supports this criterion through its “Session Recovery” and archiving features.21 By saving measurement sessions, a reliability engineer can overlay current data with historical baselines. If the “Overall Vibration” graph shows a step-change, the engineer applies Criterion II. The “Restore Last Session” feature is particularly useful here; it allows the user to recall the exact machine state from the previous month to verify if the 25% threshold has been breached.

3.3 Operational Limits: Setting ALARMS and TRIPS

The standard provides guidance for setting automated protection systems:

• ALARM: To provide a warning that a defined value of vibration has been reached or a significant change has occurred. The recommended setting is usually the baseline value + 25% of the Zone B/C boundary.
• TRIP: To initiate immediate action (shutdown). This is typically set at the Zone C/D boundary or slightly above, depending on the machine’s mechanical integrity.19

While the Balanset-1A is a portable device and not a permanent protection system (like a Bently Nevada rack), it is used to verify and calibrate these trip levels. Technicians use the Balanset-1A to measure vibration during a controlled ramp-up or induced unbalance test to ensure the permanent monitoring system triggers at the correct physical vibration levels mandated by ISO 20816-3.

Part IV: The Balanset-1A System – Technical Deep Dive

To understand how the Balanset-1A serves as a compliance tool, one must analyze its technical architecture.

4.1 Hardware Architecture

The Balanset-1A consists of a centralized USB interface module that processes analog signals from sensors before sending digitized data to a host laptop.

• ADC Module: The heart of the system is a high-resolution Analog-to-Digital Converter. This module dictates the precision of the measurement. The Balanset-1A handles signals to provide an accuracy of ±5%, which is sufficient for field diagnostics.8
• Phase Reference (Tachometer): Compliance with ISO 20816-3 often requires phase analysis to distinguish between unbalance and misalignment. The Balanset-1A uses a laser tachometer with a range of up to 1.5 meters and 60,000 RPM capability.17 This optical sensor triggers the phase angle calculation, accurate to ±1 degree.
• Power and Portability: Powered via USB (5V), the unit is intrinsically safe from ground loops that often plague mains-powered analyzers. The entire kit weighs approximately 4 kg, making it a true “field” instrument suitable for climbing gantries to reach fans.8

4.2 Software Capabilities: Beyond Simple Measurement

The software provided with Balanset-1A transforms the raw data into actionable intelligence compliant with ISO standards.

• FFT Spectrum Analysis: The standard mentions “specific frequency components.” The Balanset-1A displays the Fast Fourier Transform, breaking the complex waveform into its constituent sine waves. This allows the user to see if the high RMS value is due to 1x (unbalance), 100x (gear mesh), or non-synchronous peaks (bearing defects).21
• Polar Graphs: For balancing and vector analysis, the software plots vibration vectors on a polar plot. This visualization is critical when applying influence coefficient methods for balancing.
• ISO 1940 Tolerance Calculator: While ISO 20816-3 deals with vibration limits, ISO 1940 deals with balance quality (G-grades). The Balanset-1A software integrates a calculator where the user inputs the rotor mass and speed, and the system calculates the permissible residual unbalance in gram-millimeters. This bridges the gap between “the vibration is too high” (ISO 20816) and “here is how much weight to remove” (ISO 1940).11

4.3 Sensor Compatibility and Input Configuration

As noted in the snippet research, the ability to interface with various sensor types is key.

• Akcelerometri: The default sensors. The system integrates the acceleration signal (g) to velocity (mm/s) or double-integrates to displacement (µm) depending on the selected view. This integration is handled digitally to minimize noise drift.
• Eddy Current Probes: The system accepts 0-10V or similar analog inputs. The user must configure the transformation coefficient in the settings. For example, a standard Bently Nevada probe might have a scale factor of 200 mV/mil (7.87 V/mm). The user enters this sensitivity, and the Balanset-1A software scales the incoming voltage to display microns of displacement, allowing direct comparison with Annex B of ISO 20816-3.3

Part V: Operational Implementation: From Diagnostics to Dynamic Balancing

This section outlines a standard operating procedure (SOP) for a technician using Balanset-1A to ensure ISO 20816-3 compliance.

5.1 Step 1: Baseline Measurement and Classification

The technician approaches a 45 kW Centrifugal Fan.

• Klasifikacija: Power > 15 kW, < 300 kW. It is Group 2. The foundation is bolted to concrete (Rigid).
• Limit Determination: From ISO 20816-3 Annex A (Group 2, Rigid), the Zone B/C boundary is 2.8 mm/s.
• Mjerenje: Sensors are mounted using magnetic bases. The Balanset-1A “Vibrometer” mode is engaged.
• Proizlaziti: The reading is 6.5 mm/s. This is Zone C/D territory. Action is required.

5.2 Step 2: Diagnostic Analysis

Using the Balanset-1A FFT function:

• The spectrum shows a dominant peak at the running speed (1x RPM).
• Phase analysis shows a stable phase angle.
• Dijagnoza: Static Unbalance. (If the phase was unstable or high harmonics were present, misalignment or looseness would be suspected).

5.3 Step 3: The Balancing Procedure (In-Situ)

Since the diagnosis is unbalance, the technician utilizes the Balanset-1A’s balancing mode. The standard requires reducing vibration to Zone A or B levels.

5.3.1 The Three-Run Method (Influence Coefficients)

The Balanset-1A automates the vector mathematics required for balancing.

• Run 0 (Initial): Measure amplitude A₀ and phase φ₀ of the original vibration.
• Run 1 (Trial Weight): A known mass M_trial is added at an arbitrary angle. The system measures the new vibration vector (A₁, φ₁).

Izračun: The software calculates the Influence Coefficient α, which represents the rotor’s sensitivity to mass change.

α = (V₁ − V₀) / M_trial

Ispravak: The system computes the required correction mass M_corr to nullify the initial vibration.

M_corr = − V₀ / α

Run 2 (Verification): The trial weight is removed, and the calculated correction weight is added. The residual vibration is measured.

.11

5.4 Step 4: Verification and Reporting

After balancing, the vibration drops to 1.2 mm/s.
Check: 1.2 mm/s is < 1.4 mm/s. The machine is now in Zone A.

Documentation: The technician saves the session in Balanset-1A. A report is generated showing the “Before” spectrum (6.5 mm/s) and “After” spectrum (1.2 mm/s), explicitly referencing ISO 20816-3 limits. This report serves as the compliance certificate.

Part VI: Specialized Considerations

6.1 Low-Speed Machinery

ISO 20816-3 has special notes for machines running below 600 rpm. At low speeds, velocity signals become weak, and displacement becomes the dominant indicator of stress. The Balanset-1A handles this by allowing the user to switch the display metric to Displacement (µm) or by ensuring the lower frequency cutoff is set to 5 Hz or lower (2 Hz ideally) to capture the primary energy. The “Cautionary notes” in Annex D of the standard warn against relying solely on velocity at low speeds 23, a nuance the Balanset-1A user must be aware of by checking the “Linear” settings or low-frequency filters.

6.2 Transient Conditions: Run-Up and Coast-Down

Vibration during startup (transient operation) can exceed steady-state limits due to passing through critical speeds (resonance). ISO 20816-3 allows for higher limits during these transient phases.23

The Balanset-1A includes an experimental “RunDown” chart feature.11 This allows the technician to record vibration amplitude vs. RPM during a coast-down. This data is vital for:

• Identifying critical speeds (resonance).
• Verifying that the machine passes through resonance quickly enough to avoid damage.
• Ensuring that the “high” vibration is indeed transient and not a permanent state.

6.3 Annex A vs. Annex B: The Dual Evaluation

A thorough compliance check often requires both.

• Annex A (Housing): Measures force transmission to the structure. Good for unbalance, looseness.
• Annex B (Shaft): Measures rotor dynamics. Good for instabilities, oil whirl, wipe detection.

A technician using Balanset-1A might use accelerometers to clear Annex A requirements, then switch inputs to existing Bently Nevada probes to verify Annex B compliance on a large turbine. The ability of the Balanset-1A to serve as a “second opinion” or “field verifier” for permanent rack-based monitors is a key application in satisfying both annexes.

Zaključak

The transition to ISO 20816-3 signifies a maturation in the field of vibration analysis, demanding a more nuanced, physics-based approach to machine evaluation. It moves beyond simple “pass/fail” numbers into a realm of analyzing support stiffness, change vectors, and dual-domain (housing/shaft) measurements.

The Balanset-1A system demonstrates a high degree of alignment with these modern requirements. Its technical specifications—frequency range, accuracy, and sensor flexibility—make it a capable hardware platform. However, its true value lies in its software workflow, which guides the user through the complex logic of the standard: from background vibration correction and zone classification to the mathematical rigor of influence coefficient balancing. By effectively combining the diagnostic capabilities of a spectrum analyzer with the corrective power of a dynamic balancer, the Balanset-1A empowers maintenance teams to not only identify non-compliance with ISO 20816-3 but to actively rectify it, ensuring the longevity and reliability of the industrial asset base.