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The AE + Ultrasonics Monitoring Handbook by Trevor Holroyd
Publisher January 2000

Chapter Two

BASIC CONCEPTS AND THEORY

2.1 SOURCES OF ACTIVITY
2.1.1 Simulated sources
2.1.2 Naturally occurring sources
2.2 WAVE PROPAGATION
2.2.1 Background
2.2.2 Wave modes
2.2.3 Effect of boundaries / interfaces
2.2.4 Attenuation
2.2.5 Diffuse fields
2.2.6 Transfer function
2.3 DETECTION OF AE
2.3.1 AE transducers
a. High fidelity time domain analysis
b. Broadband frequency domain analysis
c. Resonant (narrow-band) detection
d. Accelerometer as an AE transducer - WARNING!
e. Airborne transducer
2.3.2 The preamplifier
2.4 SIGNAL PROCESSING
2.4.1 Purpose
2.4.2 Signal types
2.4.3 Threshold based signal processing
a. Counting threshold crossings
b. Burst/event signal characterisation
2.4.4 Evelope based signal processing
a. Signal magnitude and enveloping
b. Extracting the dynamic envelope
2.4.5 Statistical characterisation of continuous signals
a. Mean
b. Variance
c. Standard deviation
d. Skewness
e. Kurtosis
2.4.6 Trending
2.4.7 Signal averaging techniques
2.4.8 Source localisation
2.4.9 Defect repetition frequencies

Chapter Three

PRACTICAL ISSUES

3.1 ASSESSING A NEW APPLICATION
3.1.1 Purpose of the measurement
3.1.2 Assessing the likely signals
a. The wanted signal
b. AE background noise
c. Electromagnetic interference (EMI)
3.2 MEASUREMENT INTEGRITY AND REPRODUCIBILITY
3.2.1 Sensor positioning
3.2.2 The acoustic coupling of the sensor
3.2.3 Sensitivity and detection characteristics
3.2.4 The sensor (or transducer) cable
3.2.5 In-situ checking of detection capability
3.2.6 Machine operating conditions
3.2.7 The choice of instrument
3.2.8 Calibration
3.3 EFFECT OF RE-GREASING
3.4 PORTABLE AND PERMANENT INSTALLATION
3.5 COMPARISON OF AE AND VIBRATION

Chapter Four

EQUIPMENT AND INSTRUMENTATION

4.1 OVERVIEW
4.2 CORE PROCESSING- DIFFERENT APPROACHES
4.2.1 Peak based processing
4.2.2 Dynamic envelope based signal processing
4.3 PORTABLE SYSTEMS
4.3.1 Time domain - quick assessment
4.3.2 Time domain - data collecting
4.3.3 Frequency domain
4.4 PERMANENTLY INSTALLED SYSTEMS
4.4.1 Standard multi-channel systems
4.4.2 Building block modules
4.4.3 Bespoke systems tailored to the specific requirements
4.4.4 Multi single-channel systems
4.5 DYNAMIC ENVELOPE OUTPUT DEVICES
4.6 OEM SENSORS
4.7 INSTRUMENT RELEVANCE