At the CIGRE Paris Session in Paris on 23–28 August 2026, one exhibitor’s stand listing — Vaisala, stand A126 — ran from a multigas online DGA monitor down to a single-gas hydrogen transmitter. That line is the problem with comparing online DGA monitor brands: they share a category name, not a measurement. A nine-gas analyzer and a hydrogen-only sensor are not rival versions of one instrument, and brand searches return price aggregators, not vendor comparisons.
What does each monitor actually measure?
Photoacoustic spectroscopy (PAS) reads the pressure wave a gas makes when it absorbs modulated light. GE Vernova documents its Kelman DGA 900 as fourth-generation photoacoustic detection across nine gases plus moisture (vendor data), and Camlin documents a five-gas PAS unit (vendor data). Vaisala documents the Optimus OPT100 with patented infrared measurement, vacuum gas extraction and a total gas pressure channel (vendor data). Gas chromatography (GC) separates the mixture on a column first; Qualitrol calls the Serveron TM8 a laboratory-grade GC platform (vendor data). Selective hydrogen sensing measures one gas only; H2scan documents GRIDSCAN 5000 as self-calibrating solid-state sensing rated for ten years (vendor data). MTE documents the HYDROCAL 1005 as a four-gas-plus-moisture oil analysis system (vendor data) without naming its principle — a reason to ask.
Gas coverage and the cost of keeping it running
A hydrogen-only monitor answers “has something started” — hydrogen appears early in thermal, discharge and arcing faults alike and cannot separate them. Ethylene points to overheating and acetylene distinguishes arcing: exactly the gases a single-channel detector omits, so fault type stays unknown until a laboratory sample returns. A five-gas unit still leaves carbon dioxide, nitrogen and oxygen out, keeping cellulose involvement and air ingress invisible. See the hydrogen sensor selection guide and DGA fundamentals for both tiers.
| Principle | Gases covered | Consumables / service | Retrofit interface |
|---|---|---|---|
| Photoacoustic spectroscopy (PAS) | Nine gases plus moisture | None; no frequent recalibration (GE Vernova, Camlin — vendor data) | Valve or pump — confirm which |
| Infrared plus total gas pressure | Fault-gas set; O2/N2 optional | No carrier or calibration gas (Vaisala — vendor data) | Vacuum extraction; ask oil volume |
| Gas chromatography (GC) | Nine gases (Qualitrol — vendor data) | Carrier gas and column life | Sampling loop plus cabinet |
| Selective hydrogen sensing | Hydrogen only; moisture optional | Self-calibrating, none (H2scan — vendor data) | Sensor head on tank or valve |
| Multi-gas oil analysis | Four or five gases plus moisture (MTE — vendor data) | Not always published — ask | Valve connection G 1½″ DIN ISO 228-1 or NPT (MTE — vendor data) |
Lifetime cost diverges here. A GC-based monitor consumes carrier gas and column life by design; PAS, infrared and solid-state units do not. The DGA monitor price guide shows how far apart those paths land over a decade. Ask for site visits per year and what is replaced at each: an interval quoted in months means little without the basis behind it. Calibration must still be traceable to a reference at an interval that survives a laboratory cross-check.
Retrofit reality — and five questions to send
Most units reach the oil through an existing flange or valve, and there the similarity ends: connector standard, oil volume drawn, and the need for a cabinet or pump all differ. Modbus is close to universal; IEC 61850 is not, yet it is required if the unit must appear in a digital substation as a device, not a data source. Five questions make the answers comparable:
- Which gases do you measure, and at what detection limit?
- Which principle, and is it the same one for every gas?
- What is replaced over ten years, and what sets that interval?
- How does it connect to the oil — does installation need an outage?
- Which protocols are native, and which are paid options?
FAQ: comparing online DGA monitor brands
How do I compare vendors whose spec sheets list different gases?
Normalize: one row per gas, one column per supplier, marked measured or not with its detection limit. Cells the vendor’s own documentation cannot fill stay empty.
Is one brand’s hydrogen-only monitor the same as another’s hydrogen channel?
Not necessarily. A hydrogen channel inside a nine-gas analyzer and a dedicated hydrogen sensor can sit on different principles and drift differently. Judge each on its own document.
What should a brand comparison cover beyond the instrument?
A spare-parts path, a service response time in writing, and whether the same vendor scales from one transformer to a fleet.
Comparing brands against your own transformer list
PAS DGA spans both ends of that ladder. The hydrogen sensor range covers the screening tier with palladium thin-film sensing and no consumables; the nine-gas DGA-900 adds the full fault-gas fingerprint plus moisture. The compliance guide explains how a continuous channel sits beside the laboratory schedule. Contact PAS DGA with your transformer list and voltage classes.
Sources
- Vaisala — CIGRE Paris Session 2026 event page; Optimus™ OPT100 product page.
- GE Vernova — Kelman DGA 900 product page.
- Camlin — TOTUS G5 and TOTUS G1 product pages.
- Qualitrol — Serveron® TM8 product page.
- H2scan — Transformer Monitoring product page.
- MTE Meter Test Equipment AG — HYDROCAL 1005 product page.
- Brands whose public documentation could not be read directly are not named here.