Photoacoustic spectroscopy is an optical detection technology that measures dissolved gas concentrations directly in transformer oil.
Two core technologies power PAS DGA monitoring — photoacoustic spectroscopy (PAS) and palladium alloy thin-film sensing. Together, they deliver lab-grade accuracy with zero consumables, zero carrier gas, and zero maintenance.
Key figures at a glance
- Multi-gas monitors measure on a cycle of 1 to 24 hours (default 4 hours) — up to 6 measurements per day with no operator involvement.
- Palladium-alloy hydrogen sensors hold ±15% of reading or ±5 ppm accuracy with no routine calibration.
- The laser photoacoustic (LPAS) detection cell has no consumables and its laser diode is rated for more than 50,000 hours of continuous operation.
Photoacoustic Spectroscopy
Multi-gas DGA via the photoacoustic effect — no carrier gas, no columns, no consumables. The solid-state alternative to gas chromatography.
Palladium Thin-Film Sensors
Room-temperature H₂ detection from 2 ppm. Solid-state, no heater, no consumables, 10-year expected life.
PAS vs Gas Chromatography
Online PAS vs lab GC compared across detection limits, cost, speed and maintenance — and why the industry is shifting.
DGA Technology Comparison
PAS, GC, NDIR, FTIR, TDLAS and fuel-cell — an 8-dimension comparison to choose the right DGA technology.
Standards & Certifications
IEC 60599, IEC 60567, IEEE C57.104, IEEE C57.143 and CIGRE — the DGA standards every engineer should know.
DGA Knowledge Center
Fault gases, diagnostic methods and practical DGA guides — the complete knowledge base for transformer monitoring.
How photoacoustic spectroscopy measures dissolved gas
- Step 1: Oil reaches the cell — the monitor draws transformer oil through a closed circulation loop into a small measurement cell; no carrier gas or column is required.
- Step 2: Light pulses — a tunable semiconductor laser pulses at a wavelength absorbed by the target gas molecules.
- Step 3: Sound is generated — the absorbed light heats the gas and the resulting pressure change creates a photoacoustic signal.
- Step 4: Signal becomes a reading — the signal amplitude is converted into a gas concentration for each measured gas.
- Step 5: Report and repeat — concentrations are logged and transmitted, and the monitor repeats on its measurement cycle.
FAQ
Q: How does Laser Photoacoustic Spectroscopy (LPAS) work?
A: LPAS uses a tunable semiconductor laser tuned to specific infrared absorption wavelengths for each fault gas. When the laser pulse hits gas molecules in the measurement cell, the absorbed energy causes periodic thermal expansion, generating an acoustic pressure wave.
Q: How does temperature affect DGA readings?
A: Gas solubility in oil is temperature-dependent (Henry’s Law / Ostwald coefficient). As oil temperature increases, some dissolved gas moves from the oil phase to the gas phase.