Acoustic Imaging Glossary

Essential Terms & Definitions for Acoustic Imaging Technology

Welcome to FLIR’s Acoustic Imaging Glossary, the most comprehensive resource for understanding key terms in industrial acoustic imaging. Whether you’re a maintenance manager, reliability engineer, or safety inspector, this guide helps you navigate essential terminology related to compressed air leak detection, partial discharge monitoring, mechanical fault identification, and predictive maintenance.

A, B, C, D, E, F, G, H, I, J, K, L, M, N, O, P, Q, R, S, T, U, V, W, X, Y, Z

A

Acoustic Camera

A specialized device equipped with multiple microphones that converts sound waves into a visual representation. FLIR Acoustic Imaging Cameras are leading solutions for detecting leaks, partial discharges, and mechanical faults.

Acoustic Imaging

A non-contact diagnostic technique that uses an array of microphones to create sound-based visuals, allowing users to pinpoint compressed air leaks, pressurized gas leaks, and partial discharge from a safe distance.

Amplitude

The strength or intensity of a sound wave, measured in decibels (dB). A higher amplitude often indicates larger air leaks or more severe mechanical faults.

ATEX Zone 22 Certification

A regulatory classification for areas where explosive dust atmospheres may occur occasionally.

Auto Distance

A feature that automatically measures the distance between the camera and the detected sound source. Auto Distance improves leak quantification accuracy.

Auto Filter

Automatically selects the best frequency range settings for the environment, reducing the need for manual adjustments.

Automatic Frequency Tuning

See Auto Filter

Back to top

 

B

Band-Pass Filter

A band-pass filter (BPF) is a device that allows frequencies within a specific range to pass while blocking or attenuating frequencies outside that range. It is the opposite of a band-stop filter, which eliminates frequencies within a defined range while allowing all others to pass.

In FLIR acoustic imaging cameras, the band-pass filter enables users to manually select a specific frequency range for inspection. This helps isolate relevant ultrasonic signals while filtering out background noise, improving the accuracy of leak detection, partial discharge analysis, and mechanical fault identification in various industrial environments.

Bandwidth

Bandwidth in acoustic imaging refers to the range of frequencies that an acoustic camera can detect and process. It determines how effectively the device can identify and analyze different types of leaks, mechanical faults, and partial discharge signals.

In FLIR acoustic imaging cameras, bandwidth typically ranges from 2 kHz to 130 kHz, allowing for detection of both lower-frequency mechanical noises and high-frequency ultrasonic leaks.

Why Bandwidth Matters in Acoustic Imaging

• Wider bandwidth enables detection of a broader range of sound anomalies.
• Lower frequencies (e.g., 2 kHz - 20 kHz) are useful for identifying mechanical faults such as bearing wear and misalignment.
• Higher frequencies (e.g., 50 kHz - 130 kHz) help detect compressed air leaks, gas leaks, and electrical discharges that emit ultrasound waves.
• Proper filter selection (e.g., Norm, High, Ultra, Full) allows users to optimize the bandwidth range for specific inspection environments.

Beamforming

The basic principle used by most acoustic imaging cameras is beamforming. Beamforming focuses on sound from a specific direction while reducing background noise from other directions. By using this technique, acoustic imaging cameras create a detailed acoustic portrait, allowing users to visualize ultrasonic data even in noisy environments.

Bearing Fault Detection

A feature in acoustic cameras that identifies worn-out bearings, misalignment issues, and friction problems in rotating machinery.

Back to top

 

C

Compressed Air Leak Detection

A key application of acoustic imaging that identifies small leaks in compressed air systems, reducing energy waste and maintenance costs.

Corona Discharge

A partial discharge phenomenon in high-voltage electrical systems that can lead to insulation failure.

Crest Factor

A measurement used in mechanical fault analysis that compares the peak amplitude of a sound signal to its RMS (root mean square) value.

• Healthy bearings: Crest factor ≈ 5
• Developing faults: Crest factor ≥ 6
  Higher values indicate bearing wear or other mechanical issues.

Back to top

 

D

Decibel (dB)

The unit of measurement for sound intensity. Higher dB levels indicate stronger sound sources, which are useful for identifying leaks or electrical discharges.

Detection Threshold

The minimum sound intensity level required for an acoustic camera to register and display a sound source.

Directional Resolution

The level of precision with which an acoustic camera can identify the direction of a sound source.

Dynamic Range

The range of sound levels an acoustic camera can detect, crucial for identifying small leaks and subtle mechanical faults.

Back to top

 

F

Fast Fourier Transform (FFT)

A mathematical algorithm used in acoustic imaging cameras to break down sound waves into their frequency components, improving leak and fault identification.

Fault Condition

A qualitative assessment of mechanical faults based on acoustic data. This assessment helps technicians determine whether a machine component is operating normally or experiencing degradation.

Frequency Band Selection

See Band-Pass Filter

Full Filter

The Full filter (2 kHz to 130 kHz) utilizes the entire frequency range of the acoustic imaging camera. This mode provides the most comprehensive sound analysis, making it ideal for experienced users who need full-spectrum data for advanced diagnostics and in-depth acoustic analysis.

Back to top

 

H

High Filter

The High filter (20 kHz to 65 kHz) is optimized for general leak detection. It removes most background noise while maintaining a good detection range, making it ideal for compressed air leak detection and mechanical fault analysis in moderately noisy environments.

Back to top

 

I

IECEx Certification

The IECEx (International Electrotechnical Commission Explosive Atmospheres) certification ensures that equipment is safe for use in hazardous environments with explosive gas or dust atmospheres.

Back to top

 

K

Kurtosis

A statistical measure used in mechanical fault analysis to evaluate the distribution of sound signal samples.

• Healthy bearings: Kurtosis ≈ 0
• Faulty bearings: Kurtosis ≥ 2
  Higher kurtosis values indicate abnormal vibration patterns, which may suggest bearing wear or damage.

Back to top

 

L

Leak Cost

The estimated annual cost of a compressed air or gas leak, calculated based on its size and duration. This value helps prioritize repairs by identifying the most costly leaks.

Leak Detected

An indicator that an acoustic imaging camera has successfully identified an air, gas, or vacuum leak. The exact location, size, and severity of the leak can be visualized using FLIR’s acoustic imaging technology.

Leak Size

A quantitative estimate of the size of a detected air or gas leak, typically measured in liters per minute (l/min). This data helps maintenance teams prioritize leak repairs to reduce energy losses and operational costs.

Back to top

 

M

Manual Frequency Selection

See Band-Pass Filter

Mechanical Fault Detection

A feature in some acoustic imaging cameras, allowing operators to detect bearing failures, overheating, and misalignment in rotating equipment before they cause downtime.

Back to top

 

N

Norm Filter

The Norm filter (10 kHz to 65 kHz) is designed to remove very low and very high-frequency background noise. It is primarily used in Partial Discharge (PD) detection and Mechanical Fault detection modes, ensuring a balanced frequency range that isolates relevant sounds while filtering out irrelevant noise.

Back to top

 

P

Partial Discharge (PD) Detection

A crucial function in high-voltage maintenance, allowing professionals to detect arcing, surface discharge, and corona discharge. The Si2-Pro can classify PD severity in real-time.

Partial Discharge (PD) Pattern

A Phase-Resolved Partial Discharge (PRPD) pattern used to identify and classify electrical discharge activity in high-voltage equipment. The PRPD pattern provides insights into the type and severity of the discharge.

Partial Discharge Types

There are several types of partial discharge (PD) that can be detected using acoustic imaging:

• Negative Corona – Low-energy ionization that occurs in high-voltage environments.
• Positive & Negative Corona – A combination of ionization processes that can lead to insulation breakdown over time.
• Floating Discharge – A discharge occurring due to improperly grounded electrical components.
• Surface/Internal Discharge – A more severe form of discharge that occurs along the surface of insulation materials or within electrical components.

Predictive Maintenance

A proactive strategy using acoustic imaging cameras to detect early signs of air leaks, mechanical faults, and electrical issues before they lead to failures.

Back to top

 

S

Severity Assessment

An AI-powered function in selected acoustic imaging cameras that automatically evaluates the severity of a detected issue and recommends maintenance actions.

Severity Bar

A visual indicator on an acoustic imaging camera that represents the severity of a detected partial discharge (PD). A higher severity level indicates a greater risk of electrical insulation failure.

Sound Pressure Level (SPL)

A measure of the strength of a detected sound, typically measured in decibels (dB).

• Higher SPL values indicate stronger sound emissions, which may signal air leaks, mechanical wear, or electrical faults.

Back to top

 

T

Threshold Adjustment

A feature that lets users modify an acoustic camera’s sensitivity, helping refine leak detection.

Back to top

 

U

Ultra Filter

The Ultra filter (30 kHz to 130 kHz) is designed for use in noisy industrial environments, where strong background noise can interfere with sound detection. It enhances detection over short distances, making it particularly effective for air and gas leak detection in areas with high ambient noise levels.

Ultrasonic

Refers to sound waves with frequencies above the range of human hearing (typically above 20 kHz). Ultrasonic waves are used in acoustic imaging cameras to detect compressed air leaks, gas leaks, and partial discharge faults that are inaudible to the human ear.

Ultrasound

A type of sound wave that travels at frequencies higher than 20 kHz, making it inaudible to humans. Acoustic imaging cameras use ultrasound to detect leaks in compressed air systems, mechanical faults, and electrical discharges. Ultrasound is particularly effective in industrial environments because it enables non-contact detection of faults from a safe distance.

Back to top

Explore FLIR’s Acoustic Imaging Solutions