Two camps, one engineering trade-off
The online dissolved gas analysis (DGA) market can broadly be divided into two technology camps. The “GC camp” is built on gas chromatography — industrializing laboratory-grade precision inside a cabinet. The “optical camp” centers on optical and spectroscopic methods, prioritizing maintenance-free, consumable-free operation and a fast measurement cycle. The divergence between the two is an engineering trade-off between two philosophies, not a simple distinction of superiority.
The GC camp: mature precision, with consumables
The GC camp is represented by Qualitrol’s Serveron TM8 (vendor data). It integrates mature gas chromatography into a cabinet, using helium carrier gas and a chromatography column for high-precision separation. It measures 8 gases plus N2, has a C2H2 lower detection limit (LDL) of 1 ppm, and a normal measurement cycle of about 4 hours, shorten-able to about 1 hour under fault conditions.
The GC route is technically mature, has a large installed base, and enjoys high acceptance among power utilities. The trade-off: the carrier gas and chromatography column are consumables requiring periodic replacement, which raises operation and maintenance cost and lengthens maintenance cycles. Its 1 ppm C2H2 limit also leaves room for improvement in early-warning scenarios for low-energy discharge.
The optical camp: maintenance-free by design
The optical camp can be subdivided by detection principle. Representative infrared photoacoustic (PAS) products include Doble’s Calisto series and Camlin’s TOTUS. The Calisto R9 uses an infrared photoacoustic (DIPAS) scheme combined with thermal conductivity and features water-vapor self-calibration (vendor data). The Camlin TOTUS G9 measures 9 gases plus moisture, has a C2H2 LDL of 0.1 ppm, a selectable measurement cycle from 1 hour to 1 day, and claims no calibration gas and no carrier gas.
Representative of non-dispersive infrared (NDIR) is the Vaisala OPT100: NDIR combined with vacuum degassing, 7 gases plus moisture (O2/N2 optional), C2H2 detection accuracy of ±0.5 ppm, positioned as “maintenance-free,” with total gas pressure (TGP) support.
Laser photoacoustic spectroscopy (L-PAS) is a niche direction that has emerged in recent years. Commercial L-PAS systems feature a full standard configuration of 9 gases plus moisture, a C2H2 LDL of ≤0.1 ppm — with the commercial L-PAS class citing 0.05 ppm (vendor data) — and no carrier gas, no consumables, and zero oil consumption.
OEM-integrated monitoring: a third force
Transformer main-unit manufacturers are bundling online monitoring with the main unit as a combined offering. GE Vernova (DGA 900 Plus), Hitachi Energy (TXpert), and Siemens (Sensformer) offer DGA monitoring as an optional accessory or factory-integrated component (vendor data). The advantage of this model is factory integration and a unified warranty; its limitation is limited cross-vendor adaptation, so retrofitting the large existing fleet still depends on independent monitoring vendors.
Representative products at a glance
| Vendor / product | Technology | Gas coverage | C2H2 LDL | Measurement cycle | Consumables |
|---|---|---|---|---|---|
| Qualitrol Serveron TM8 | Gas chromatography (GC) | 8 gases + N2 | 1 ppm | 4 h (1 h in fault) | Helium + column |
| Doble Calisto R9 | Infrared photoacoustic (DIPAS) + thermal conductivity | Multi-component | — | — | None |
| Camlin TOTUS G9 | Photoacoustic (PAS) | 9 gases + moisture | 0.1 ppm | 1 h–1 day | None |
| Vaisala OPT100 | NDIR + vacuum degassing | 7 gases + moisture (O2/N2 optional) | ±0.5 ppm | 1–1.5 h | None (maintenance-free) |
| Commercial L-PAS | Laser photoacoustic (L-PAS) | 9 gases + moisture | ≤0.1 ppm (0.05 ppm) | Continuous online | None |
Product parameters above are taken from public vendor materials (vendor data).
Reading the trade-offs, and where PAS DGA sits
Neither camp is categorically “better.” The GC route remains competitive in the stock market and in certain high-accuracy application scenarios; the optical route — especially photoacoustic and laser photoacoustic — is moving toward the mainstream through maintenance-free operation, high sensitivity, and fast cycles. The market remains fragmented: no single vendor holds a dominant share.
Competition centers on the balance across lower detection limit, gas coverage, consumable and maintenance cost, measurement cycle, communication protocol compatibility, and long-term stability. The PAS DGA-900 takes the L-PAS route: 9 gases plus moisture, no consumables, and continuous online measurement. For the physics behind that choice, see photoacoustic spectroscopy and our fourth-generation L-PAS explainer. For a lifecycle-cost view across technology routes, see our online DGA monitor TCO comparison.
PAS DGA for online DGA monitoring
The PAS DGA-900 measures 9 gases plus moisture with L-PAS, needs no carrier gas and no calibration gas, and supports MODBUS, IEC 61850, IEC 60870-5-104, and DNP3.0. For help positioning your monitoring program across the GC/optical trade-off, contact PAS DGA.