Foreword

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This document was prepared by Technical Committee ISO/TC 108, Mechanical vibration, shock and condition monitoring, Subcommittee SC 5, Condition monitoring and diagnostics of machine systems.

This second edition of ISO 29821 cancels and replaces the first edition ( ISO 29821:2018 ) which has been technically revised.

The main changes are as follows:

Clause 5 has been revised to include Formula (1) describing the decibel level;
Clause 5 has been revised to include MEMS sensors and a reference to ISO 1683 ;
Subclause 5.3 has an additional note describing parabolic reflectors;
Figures B.1 to B.4 have been improved;
Minor editorial changes have been made.

Any feedback or questions on this document should be directed to the user’s national standards body. A complete listing of these bodies can be found at www.iso.org/members.html.

Introduction

This document provides specific guidance on the interpretation of ultrasonic readings and wave files or frequency and time domain printouts (sometimes called sound characteristics) as part of a programme for condition monitoring (CM) and diagnostics of machines.

Airborne (AB) and structure-borne (SB) ultrasound can be used to detect abnormal performance or machine anomalies. The anomalies are detected as high frequency acoustic events caused by turbulent flow, ionization events, impacts and friction which are caused by incorrect machinery operation, leaks, improper lubrication, worn components, and/or electrical discharges.

Airborne and structure-borne ultrasound is based on measuring the high frequency sound that is generated by either turbulent flow, friction, impacts or ionization created from the anomalies. Personnel carrying out ultrasonic inspections or measurements therefore require an understanding of ultrasound and how it propagates through the atmosphere and through structures as a prerequisite to the creation of an airborne and/or structure-borne ultrasound programme.

Ultrasonic energy is present with the operation of all machines. It can be in the form of friction, turbulent flow, impacts and/or ionization as a property of the process or produced by the process itself. As a result, ultrasonic emissions are created which are a useful parameter for monitoring machine condition and detecting anomalies.

1 Scope

This document

gives guidelines for establishing severity assessment criteria for anomalies identified by airborne (AB) and structure-borne (SB) ultrasound,
specifies methods and requirements for carrying out ultrasonic inspection, testing, measurement and monitoring of machines, including safety recommendations and sources of error, and
provides information relative to data interpretation, assessment criteria and reporting.

2 Normative references

3 Terms and definitions

4 Principle of the airborne and structure-borne method

4.1 General

4.2 Application of airborne and structure-borne ultrasound within condition monitoring programmes

4.3 Correlation with other technologies

5 Ultrasound equipment

5.1 General

5.2 Types of sensor

5.3 Airborne sensor choice

5.4 Structure-borne sensor choice

5.5 Instrument characteristics

6 Data collection guidelines

6.1 General

6.2 Comparative ultrasound

6.3 Baseline method — Quantitative ultrasound

7 Training requirements

8 Assessment criteria

8.1 General

8.2 Error sources, accuracy and repeatability

9 Interpretation guidelines

10 Diagnosing ultrasonic problems

10.1 Ultrasound diagnostic principles

10.2 Generation of ultrasound

11 Sensitivity validation guidelines

12 Monitoring interval

13 Alternative CM techniques

14 Reporting

Bibliography