Infrared DGA and Aging Oils: Possible Without Recalibration?
Infrared measurement makes a maintenance-free DGA monitor possible — if the challenge of oil aging is solved. This note explains why aged oils interfere with the measurement and how autocalibration removes the need to recalibrate.
Infrared technologies — NDIR or photoacoustic (PAS) — are a proven basis for online dissolved gas analysis, with an additional appeal: they make a maintenance-free DGA monitor possible, with no consumables or carrier gases and no field recalibration. On one condition — solving the challenge of oil aging.
This note explains what that challenge is and how it is solved. For the general context of the technique, see the dissolved gas in oil instrumentation landing and the note on the role of online DGA monitoring.
This note covers
- Why aged oils interfere with infrared measurement
- How autocalibration compensates for interfering gases
- What it means in service: long-term stability without recalibration
The Challenge: Oils That Age
Transformer oil is neither a simple nor a stable substance: it is a complex mixture of hydrocarbons whose chemical composition deteriorates over the years due to oxidation, thermal stress and other aging mechanisms. That deterioration generates new compounds within the oil itself.
The problem for infrared measurement is that several of these aging hydrocarbons absorb light at wavelengths that overlap with the fault gases' absorption signatures. If the instrument does not compensate for it, that interference translates into erroneous concentrations — and in DGA, an erroneous reading means wrong fault diagnoses or false alarms.
The Solution: Autocalibration
The traditional approach to containing that drift is recalibrating the instrument periodically — a costly procedure that interrupts monitoring and, on a remote asset, involves field logistics. The alternative built into the Optimus™ OPT100 monitor is autocalibration: the instrument frequently and automatically analyzes the oil composition, identifies the interfering gases and compensates for their effect on the measurement.
With the interference compensated on every measurement cycle, the need for recalibration disappears entirely: the monitor keeps its accuracy even as the oil continues to age, with no field intervention and no return to factory.
What It Means in Service
For the operator, the result is long-term stability with maintenance-free operation: the monitor delivers consistent results throughout the transformer's life, with no offline recalibration procedures and no monitoring blackout windows.
The underlying point is that the viability of recalibration-free infrared DGA does not depend on the sensor in isolation but on the complete system: the quality of the optics, the measurement reference, and the ability to analyze and compensate for the real oil matrix being measured. That combination is what turns a laboratory technology into a reliable field instrument.
This technical content is based on the Vaisala article "Infrared DGA and aging oils – possible without recalibration?" by Senja Leivo (Senior Industry Expert). AKRIBIS is an authorized Vaisala partner for distribution and technical support in the region — explore the full Vaisala instrumentation line. To evaluate the right DGA technology for your application, consult a specialist.
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