Factors That Affect Acoustic Detection Range

The detection range of an acoustic camera is not a single number. It varies significantly depending on:

• Leak/Discharge intensity: A large compressed air leak at 12 bar produces a much stronger acoustic signal than a small SF6 seepage at 2 bar
• Frequency content: Higher frequency signals (>40 kHz) attenuate more rapidly in air than lower frequencies (<20 kHz). The GSW Series covers 2 kHz to 100 kHz, balancing range with sensitivity
• Background noise: Industrial environments with operating machinery create ambient noise that can mask weak acoustic signals
• Microphone array size: Larger arrays (136 microphones in GSW Series) provide better signal-to-noise ratio through beamforming gain, extending effective range
• Weather conditions: Wind, temperature gradients, and humidity affect sound propagation outdoors

"In our field tests across Latin American substations and industrial plants, we consistently find that the practical detection range of the GSW Series for compressed air leaks is 15-30 meters under normal conditions. For partial discharge in switchgear, the range is typically 5-15 meters depending on PD intensity. These ranges cover the vast majority of practical inspection scenarios."

— Unitech Tools Field Application Report

Compressed Air Leak Detection Range

Compressed air leaks are among the easiest acoustic signals to detect because industrial compressed air systems typically operate at 6-12 bar, producing strong ultrasonic signals. The practical detection ranges are:

Leak Size	Orifice Diameter	Flow Rate (at 7 bar)	Detection Range (GSW Series)	Recommendation
Large	>1.0 mm	>50 L/min	30-50 m	Routine screening from walkways
Medium	0.5-1.0 mm	10-50 L/min	15-30 m	Standard scanning distance
Small	0.1-0.5 mm	1-10 L/min	5-15 m	Closer inspection needed
Very Small	<0.1 mm	<1 L/min	1-5 m	Point-blank with FA611S

For routine compressed air leak audits, the recommended scanning methodology is to follow the compressed air distribution lines at 10-20 meters distance. The GSW Series can identify most significant leaks (>5 L/min) from this distance, with closer inspection reserved for smaller leaks once the initial survey is complete.

Partial Discharge Detection Range

Partial discharge (PD) detection with acoustic cameras is a different challenge than compressed air leaks. PD signals in switchgear and transformers are typically intermittent and lower in amplitude. Detection ranges depend on the PD type:

PD Type	Typical Frequency Range	Detection Range (GSW Series)	Notes
Surface Discharge (Switchgear)	10-40 kHz	5-15 m	Most detectable PD type
Internal Discharge (Cable terminations)	5-20 kHz	3-10 m	Signal attenuated by enclosure
Corona (Airborne)	1-20 kHz	10-25 m	Continuous, relatively strong
Floating Potential	5-30 kHz	5-15 m	Intermittent, requires patience
Transformer PD (internal)	2-10 kHz	1-5 m	Weak through tank wall

The SW136 acoustic camera variant offers specific optimizations for partial discharge detection in substation environments, with enhanced signal processing for the intermittent signals typical of PD activity. For switchgear PD surveys, the combination of an acoustic camera plus a SC Series PD detector using TEV sensors gives the most comprehensive coverage.

Corona Discharge Detection Range

Corona discharge on transmission lines produces a distinctive acoustic signature that is particularly well-suited to acoustic camera detection. Because corona is a continuous discharge occurring at 50/60 Hz, it creates a steady acoustic signal that the beamforming algorithm can lock onto easily.

For transmission line corona detection, the GSW Series can detect and locate corona from:

• Distribution lines (13-34 kV): 10-20 meters range
• Sub-transmission lines (69-138 kV): 15-30 meters range
• Transmission lines (230-500 kV): 20-50 meters range (stronger corona at higher voltages)

This makes acoustic cameras an effective tool for vegetation management teams and line maintenance crews who need to identify corona sources from a safe distance or from the ground without climbing towers.

Gas Leak Detection Range

As discussed in the companion article "Can an Acoustic Camera Detect Gas Leaks?", the detection range for gas leaks varies significantly by gas type and pressure:

• SF6 (3-7 bar in GIS): 5-20 meters detection range. Most SF6 leaks in GIS switchgear are detectable from 5-15 meters
• Compressed air (6-12 bar): 15-30 meters (same as air leak section above)
• Refrigerant (8-25 bar high side): 5-15 meters for typical leaks in chiller rooms
• Natural gas (1-4 bar distribution): 2-10 meters due to lower pressure differential

GSW Series vs SW136 vs FA611S Range Comparison

Model	Microphone Count	Compressed Air Leak	PD Detection	Corona	Gas Leak (SF6)	Best For
GSW Series	136	30-50 m	5-15 m	20-50 m	5-20 m	General purpose, gas plants, utilities
SW136	136	25-40 m	8-20 m	25-50 m	5-15 m	Substation PD, switchgear surveys
FA611S	136	35-60 m	5-15 m	30-60 m	8-30 m	Long-range survey, low-pressure leaks

All three models use the same 136-microphone MEMS array. The differences in detection range come from signal processing algorithms and frequency response tuning. The FA611S offers the longest detection range for compressed air and corona applications thanks to its enhanced low-frequency sensitivity.

Practical Tips for Maximizing Detection Range

To get the maximum detection range from your acoustic camera:

• Start at maximum distance, then move closer: Begin your survey at 20-30 meters to identify obvious leaks, then reduce distance for smaller leaks
• Use the frequency filter: If background noise is an issue, restrict the frequency band to the 35-45 kHz range where compressed air and gas leaks produce the strongest signals
• Minimize wind interference: When surveying outdoors, position yourself upwind of the target area. Wind speeds above 20 km/h significantly reduce effective range
• Combine with other methods: For PD detection, use the acoustic camera for initial screening at 5-15 meters, then confirm with a SC Series TEV detector for quantitative measurement
• Train operators: Detection range is operator-dependent. Experienced operators can identify weak signals that novice operators miss. Investing in operator training directly improves effective detection range

"We surveyed a 230 kV substation in Colombia with the GSW Series. From the perimeter walkway (25 meters from the nearest bay), we identified 3 corona sources, 1 SF6 leak, and 2 loose connection PD signals. Moving to 10 meters for detailed inspection confirmed all findings. The initial long-range survey took 20 minutes; the detailed inspection took 45 minutes. Total survey time for a 4-bay substation: just over one hour."

— Unitech Tools Case Study: Colombian Transmission Utility