ISO 13373-1: Condition Monitoring and Diagnostics of Machines — Vibration Condition Monitoring, Part 1: General Procedures

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ISO 13373-1 establishes a systematic, repeatable procedure for performing vibration measurements and analysis as part of a condition monitoring programme. It is the foundational “how-to” guide for the practical mechanics of measurement: how to choose measurement points and parameters, how to acquire the data, and how to carry out a first level of evaluation. Its goal is to guarantee that the vibration data you collect is consistent, reliable and suitable for detecting changes in a machine’s condition over time. Where ISO 17359 sets the overall strategy for a monitoring programme, ISO 13373-1 fills in the procedural detail for the vibration channel and formalises the best practices behind route-based data collection.

1. Scope and Objectives

This foundational chapter defines the standard’s purpose: to establish a generic, systematic and repeatable set of procedures covering the whole process of vibration condition monitoring. The primary objective is to ensure data is acquired consistently and reliably, so it is fit for its intended use — detecting changes in a machine’s dynamic behaviour as they develop. The document is designed to be the procedural backbone for setting up a new programme or auditing an existing one.

The underlying message is that following these procedures lets an organisation build a high-quality database of machine vibration history. That history is the essential prerequisite for effective fault detection, trend analysis and diagnostics. The standard is explicit that Part 1 covers the general methodology, while subsequent parts — notably ISO 13373-2 — provide the more detailed diagnostic techniques that interpret the data once it has been correctly gathered.

2. Measurement and Sensor Selection

This chapter governs the decisions that form the foundation of any measurement. It mandates a structured approach to choosing measurement points, stressing that they should sit as close as possible to the machine’s bearings so they faithfully capture the forces transmitted from the rotor. It gives detailed guidance on measurement orientation — horizontal, vertical and axial — to build a complete three-dimensional picture of how the machine moves.

A significant part of the section addresses sensor choice and the trade-offs between transducer types. The accelerometer is identified as the most common choice for its wide frequency range and robustness, but the standard also discusses velocity transducers and non-contact proximity probes for specific applications such as fluid-film-bearing machines. Crucially, it stresses that data quality depends directly on how the sensor is mounted, strongly recommending permanent stud mounting for the most repeatable results and referencing the detailed mounting guidelines in ISO 5348.

3. Measurement Parameters

This is arguably the most technical section, because it dictates the settings inside the data collector that determine the quality and usefulness of the spectral and waveform data. It offers a methodology for selecting those settings around the specific machine and the faults being watched for:

• Frequency range (F_max): the maximum frequency for the measurement must be high enough to capture the signatures of interest — the high-frequency tones of bearing defects or gear mesh — yet not so high that it dilutes resolution with needless noise.
• Resolution: the number of lines in the FFT spectrum. Sufficient resolution is needed to separate closely spaced components, which is critical for resolving the sidebands around a gear-mesh frequency or distinguishing near-identical running speeds in a multi-shaft machine.
• Averaging: signal averaging improves the signal-to-noise ratio and yields a more stable, repeatable measurement. The standard describes the different forms — RMS averaging and peak hold among them — and when each is appropriate.
• Windowing: it explains why a windowing function such as a Hanning window must be applied to the time data before the FFT, in order to minimise the error known as spectral leakage.

Choosing F_max and line count together fixes the frequency span of each spectral bin, so the two settings are best decided as a pair; an FFT resolution calculator makes that trade-off explicit before a route is configured.

4. Data Acquisition Procedures

This chapter moves from setup to execution, providing a rigorous procedure for the act of collection itself. The central concern is comparability: every measurement must be directly comparable with all past and future measurements at the same point. The standard therefore places strong emphasis on documenting the machine’s operating conditions at the moment of the test — rotational speed, load, temperature and any other relevant process variables. This context matters because a shift in operating conditions can change a machine’s vibration signature significantly, and without it a benign change could be misread as a developing fault. The chapter also supplies a checklist for verifying the integrity of the measurement chain before recording: confirming the sensor is properly mounted, the cable is sound, and the collector’s settings are correct.

5. Data Analysis and Evaluation

Once high-quality data exists, this chapter frames its interpretation, formalising the two-pronged approach first introduced in standards such as ISO 20816-1 (the modern successor to ISO 10816-1):

• Absolute limit comparison: the measured broadband value is checked against predefined severity charts — for example the zones of the ISO 20816 series — to classify the machine as Good, Satisfactory or Unsatisfactory.
• Trend analysis: the more powerful method, plotting values over time to establish a stable baseline and then watching for significant deviation from it. The standard stresses that detecting a change is often more important than the absolute number.

It provides the methodology for setting data-driven alarm thresholds: an Alert might be raised when vibration doubles (a 100% rise over baseline) and a Trip when it quintuples (a 400% rise), even while the absolute values still sit inside an otherwise acceptable zone. This change-based logic catches faults that a fixed limit alone would miss until much later.

6. Basic Fault Identification

The final chapter is an introduction to the diagnostic process. While Part 1 concentrates on acquisition and detection, this section bridges toward diagnostics by explaining the fundamental principle that different mechanical and electrical faults generate unique, recognisable patterns in the vibration data. It introduces the practice of correlating specific frequencies in the FFT spectrum with their physical sources on the machine. A dominant peak at exactly one times running speed (1X) typically indicates unbalance; a strong peak at 2X often points to misalignment; and high-frequency, non-synchronous peaks are commonly associated with bearing defects. This grounding is what an analyst needs before tackling the deeper root-cause analysis covered by the more advanced standards in the ISO 13373 series.

7. Putting the Procedure to Work in the Field

Following ISO 13373-1 in practice means carrying an instrument that can both acquire spectra to the standard’s parameter rules and document the operating conditions alongside each reading. A portable two-channel analyser such as the Balanset-1A measures the broadband levels and FFT spectra the standard calls for, captures the synchronous 1X amplitude and phase that distinguish unbalance from misalignment, and lets the technician record speed and load with each point so later comparisons stay valid. When the analysis in Section 5 confirms an unbalance fault, the same tool performs the field balancing correction on site, keeping the detect-and-correct cycle in one place.

8. Key Concepts to Remember

• Consistency and repeatability: the central theme of the standard — a monitoring programme is worthless if its data is gathered inconsistently, and ISO 13373-1 supplies the rules that make it consistent.
• Data quality: the standard dwells on the factors that govern quality, above all transducer mounting and the correct choice of measurement settings such as frequency range and resolution.
• Foundation for a programme, not a diagnostic manual: it does not tell you how to identify every specific fault; it is the essential first step that tells you how to collect the data that diagnostics — covered in ISO 13373-2 and -3 — will later interpret.

The complete official text is published by ISO as standard reference 21831 and may be purchased from the ISO store. The summary above captures its procedural logic; organisations needing the full normative detail, exact competency criteria and all technical specifications should obtain the standard itself.

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