Threshold Setting Trade-offs

Selecting an appropriate threshold involves balancing sensitivity and noise rejection.

Threshold Too Low

If the threshold is set too low:

• Environmental noise may trigger hits
• Data volume increases significantly
• False indications become more common

Typical Consequences

• Unstable monitoring
• Difficult data interpretation
• Reduced confidence in results

Threshold Too High

If the threshold is too high:

• Weak signals may not be detected
• Early-stage damage may be missed
• Detection sensitivity decreases

Typical Consequences

• Loss of important information
• Delayed damage detection

Understanding Gain

What Is Gain?

Gain is the amount of amplification applied to the AE signal before processing.

AE system usually use preamplifier right after sensors. The gain is one of the important specs of the preamplifier. It is typically expressed in decibels (dB).

Purpose of Gain

Gain is used to:

• amplify weak AE signals,
• improve signal detectability,
• and optimize system dynamic range.

How Gain Affects Signals

Higher gain increases signal amplitude before digitization.

This can:

• improve detection of small events,
• but also amplify background noise.

Gain Setting Trade-offs

Gain Too Low

If gain is too low:

• Weak signals may remain below threshold
• Detection sensitivity decreases

Typical Consequences

• Missed microcracks or low-energy events

Gain Too High

If gain is too high:

• Noise becomes amplified
• Signal distortion or saturation may occur

Typical Consequences

• Increased false hits
• Reduced measurement accuracy

Relationship Between Threshold and Gain

Threshold and gain must always be considered together.

Key Interaction

• Increasing gain effectively raises signal amplitudes
• Lowering threshold increases detection sensitivity

These parameters jointly determine:

• what signals are detected,
• and what signals are ignored.

Example Scenario

Case 1: Low Gain + High Threshold

• Very few hits detected
• Weak damage activity may be missed

Case 2: High Gain + Low Threshold

• Large number of hits
• Noise may dominate data

Case 3: Balanced Settings

• Relevant signals captured
• Noise reasonably controlled

This balance is the goal of practical AE setup.

Typical Threshold Values

Threshold settings vary depending on:

• sensor sensitivity,
• pre-amplifier gain,
• environment,
• and application.

Common Ranges

• Laboratory testing: lower thresholds
• Industrial environments: higher thresholds

There is no universal threshold suitable for all applications.

Typical Gain Values

Common pre-amplifier gain values include:

• 20 dB
• 40 dB
• 60 dB

Higher gain is often required for:

• weak signals,
• long sensor distances,
• or highly attenuating materials.

Factors Affecting Threshold and Gain Selection

1. Noise Environment

High-noise environments require:

• higher thresholds,
• or lower gain.

2. Signal Attenuation

Structures with strong attenuation may require:

• higher gain,
• or closer sensor spacing.

3. Monitoring Objective

Early Damage Detection

• Lower threshold
• Higher sensitivity

Long-Term Industrial Monitoring

• More conservative settings
• Better noise rejection

4. Sensor Type

• Resonant sensors often allow lower thresholds due to better sensitivity
• Broadband sensors may require more careful noise management

Threshold and Gain in Source Characterization

Threshold and gain settings affect measured signal parameters such as:

• amplitude,
• duration,
• counts,
• and energy.

Because of this:

AE data collected using different settings may not be directly comparable.

Consistent setup is important for reliable trend analysis.

Practical Setup Recommendations

Initial Setup Strategy

• Observe background noise level
• Set threshold slightly above stable noise
• Adjust gain to detect expected signals
• Verify using simulated sources (e.g., pencil lead break)

During Monitoring

During Monitoring

Threshold and gain may require adjustment if operating conditions change.

• hit rate,
• waveform quality,
• and false trigger frequency.

Common Mistakes

Setting Threshold Too Low

Creates excessive false hits and unstable data.

Using Excessive Gain

Amplifies both signals and noise, sometimes causing saturation.

Ignoring Environmental Changes

Temperature, machinery activity, and operational conditions can alter noise levels over time.

Frequently Asked Questions

Is lower threshold always better?

No. Lower thresholds improve sensitivity but may significantly increase noise detection.

Does higher gain improve monitoring performance?

Not always. Excessive gain may amplify unwanted noise and distort signals.

Should threshold and gain remain constant?

For consistent analysis, stable settings are preferred unless environmental conditions change significantly.

Can threshold remove all noise?

No. Threshold helps reduce noise, but additional filtering and signal analysis are usually required.

Related Topics

• Acoustic Emission Signal Processing
• Noise Discrimination Methods
• Acoustic Emission Sensors Overview
• AE Hit and Signal Features

Summary

Threshold and gain are essential parameters in acoustic emission monitoring systems that determine signal detectability and noise rejection. Threshold defines the minimum signal level required for detection, while gain controls signal amplification. Proper adjustment of these parameters is critical for balancing sensitivity, reliability, and data quality in both laboratory and industrial monitoring applications.