ISO 20816-1: Mechanical vibration – Measurement and evaluation of machine vibration – Part 1: General guidelines

Summary

ISO 20816-1 is the current, modern international standard that provides the general guidelines for measuring and evaluating machinery vibration. It is a significant update as it supersedes and combines the principles of two older, foundational standards: ISO 10816-1 (which covered measurements on non-rotating parts) and ISO 7919-1 (which covered measurements on rotating shafts). This new standard provides a unified framework for assessing the vibration of a machine as a whole, considering both casing and shaft measurements together for a more comprehensive evaluation.

Table of Contents (Conceptual Structure)

The standard integrates and updates the concepts from its predecessors into a cohesive structure:

1. 1. Scope and Measurement Types:

   This initial chapter defines the standard’s comprehensive scope, establishing it as the primary guide for assessing the vibration of a wide range of industrial machinery under operational conditions. Its most significant feature is the formal unification of two distinct measurement philosophies. It provides detailed methodologies for measuring vibration on both:

   • Non-rotating parts: This refers to measurements taken on the stationary components of a machine, typically the bearing housings. The standard reaffirms that the preferred metric for this type of measurement is broadband RMS (Root Mean Square) velocity, measured with seismic sensors like accelerometers. This measurement reflects the destructive energy being transmitted to the machine’s structure.
   • Rotating shafts: This refers to measurements of the dynamic movement of the shaft itself, relative to a fixed point (usually the bearing housing). The standard specifies that this must be measured with non-contact proximity probes, and the preferred metric is Peak-to-Peak displacement. This measurement directly quantifies how much the shaft is moving within its bearing clearance.
2. 2. Instrumentation:

   This chapter specifies the technical requirements for the entire measurement system to ensure accuracy and consistency, covering both seismic (casing) and non-contact (shaft) measurements. It mandates that the instrumentation, including the transducer, cabling, and analyzer, must be capable of accurately measuring the specified parameters (RMS velocity or Peak-to-Peak displacement) over the required frequency range for the machine type. The standard emphasizes the importance of regular calibration of the entire measurement chain against a known, traceable standard. Furthermore, it provides critical guidance on proper sensor installation, referencing specific standards for mounting accelerometers (ISO 5348) and proximity probes (e.g., API 670) to minimize measurement error and ensure data is reliable and repeatable over time.

3. 3. Evaluation Criteria:

   This section forms the core of the evaluation methodology, carrying forward the proven two-criterion approach from earlier standards. It provides a detailed framework for assessing machine condition based on both absolute values and changes over time:

   • Criterion 1 (Absolute Limits): This criterion involves comparing the absolute measured vibration magnitude (either casing velocity or shaft displacement) against pre-defined limits. These limits are typically established based on statistical data from a large population of similar machines or based on specific guidance from other parts of the ISO 20816 series. It serves as a fundamental benchmark for overall machine health and is critical for acceptance testing.
   • Criterion 2 (Change from Baseline): This criterion focuses on the change in vibration magnitude from a known, stable reference or baseline condition. The standard emphasizes that a significant change, even if the absolute value is still considered acceptable under Criterion 1, is often the earliest and most reliable indicator of a developing fault. This criterion is the foundation of trend-based predictive maintenance.
4. 4. Evaluation Zones:

   To simplify the application of Criterion 1, the standard continues to use the well-established four-zone framework for classifying the absolute severity of vibration. These zones provide a clear, color-coded method for communicating machine condition. It is important to note that this general part of the standard only defines the *concept* of the zones; the specific numerical values for the zone boundaries are provided in the machine-specific parts of the standard (e.g., ISO 20816-3). The zones are defined as:

   • Zone A: The vibration of newly commissioned or refurbished machinery would typically fall into this zone.
   • Zone B: Machines with vibration within this zone are normally considered acceptable for unrestricted long-term operation.
   • Zone C: Machines with vibration within this zone are normally considered unsatisfactory for long-term continuous operation. Remedial action should be scheduled.
   • Zone D: Vibration values within this zone are normally considered severe enough to cause damage to the machine.
5. 5. Combined Assessment and Acceptance:

   This final section provides a crucial synthesis of the standard’s principles. It formally recommends a combined assessment approach, especially for critical machinery equipped with both seismic and non-contact probes. It guides the user to evaluate both the casing vibration (reflecting forces transmitted to the structure) and the shaft vibration (reflecting the rotor’s dynamic behavior) to form a more complete and reliable judgment of the machine’s overall health. This section also clearly distinguishes between the criteria used for acceptance testing (for new or repaired machines), which typically demands that vibration levels fall within the stricter Zones A or B, and the criteria for operational monitoring of in-service machines, where established alarm setpoints (Alert and Trip) based on both absolute limits and significant changes from baseline are the primary tools for day-to-day condition assessment.

Key Concepts

• Unification of Standards: The most important aspect of ISO 20816-1 is that it replaces and unifies the previously separate standards for casing (ISO 10816-1) and shaft (ISO 7919-1) vibration. This promotes a more holistic approach to machinery analysis.
• Dual-Measurement Philosophy: The standard strongly advocates for using both casing and shaft vibration measurements where possible, as they provide complementary information. High casing vibration might indicate a structural issue, while high shaft vibration might indicate a rotor-dynamic problem.
• Modernization: It updates the general guidelines to reflect modern instrumentation and data analysis practices that have evolved since the original standards were published.
• Foundation for Specific Parts: Like its predecessors, this “Part 1” standard provides the general framework. Specific numerical limits for the evaluation zones for different types of machines are detailed in other parts of the ISO 20816 series (e.g., ISO 20816-3 for industrial machines).

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