Oxygen Purity Analyser for ASU Plants

Quick answer

An online oxygen purity analyser reads 95 to 100 % O2 on the product line of an air separation, PSA or VPSA plant. ACCURRA-S 3090 and 3190 correct the reading for ambient pressure and temperature, cutting an uncompensated day-and-night error of up to 10 % to below 0.5 %.

Updated 2 November 2026 · Figures from Sarvesh datasheets

The measurement and why it matters

High-purity oxygen is hard to measure well, and the reason is the weather. Oxygen sensors respond to the amount of oxygen in the sensing volume, which depends on pressure. When barometric pressure falls by 5 percent, the partial pressure of oxygen falls by 5 percent, even though the gas is exactly as pure as before. The ACCURRA-S catalogue notes that a day and night ambient pressure variation can give rise to a 10 percent error in an uncompensated reading above 90 percent oxygen.

ACCURRA-S 3090 and 3190 measure ambient pressure and temperature inside the analyser and correct the reading. With the compensation the error is reduced to below 0.5 percent. That matters most near the top of the scale, where an allowed impurity of half a percent is the whole margin.

The same hardware platform serves the rest of an air separation plant. Trace oxygen on nitrogen and argon lines uses model 3015, dew point on dry product uses M015, and helium or argon purity can be measured by ACCURRA-TCD.

Models and ranges

Model	Measures	Range	Sensor and notes
3090	Oxygen purity	0 to 100 %, compensated	Electrochemical, pressure and temperature compensated
3190	Oxygen purity	95 to 100 %	Paramagnetic sensor, pressure and temperature compensated
3030	Oxygen percentage	0 to 25 % and 0 to 100 %	Electrochemical
3130	Oxygen percentage	0 to 100 %	Paramagnetic
3015	Trace oxygen	0 to 1000 ppm (min range 0 to 100 ppm)	Electrochemical
M015	Dew point	-80 to +20 C	Ceramic sensor
ACCURRA-TCD	He or Ar purity	Binary mixtures	Thermal conductivity, no reference gas

Process notes

Cryogenic plants: product line, column and liquid draw

A cryogenic plant cools and liquefies air, then separates oxygen, nitrogen and argon by distillation. Gaseous oxygen typically leaves at purities well above 99 percent, and the plant sells it as gas or liquid. Analysers sit on the gaseous product, and where the sample is drawn from liquid, a cryogenic vaporiser turns the draw into gas before the analyser so that the light components do not boil off first.

SV-200, our cryogenic sample vaporiser, does this with a bypass line for quick flushing.

VPSA and PSA oxygen

Vacuum and pressure swing adsorption plants produce oxygen at lower purity, typically in the low 90s. For these streams use the percentage models, 3030 or 3130 across 0 to 100 percent. See the medical oxygen plant page for the pharmacopoeia ranges.

Sampling and installation

Models 3130 and 3190 are supplied without an internal sample pump, which suits pressurised product lines. Tell us the sample pressure and we will confirm the sample path.
Every ACCURRA-S has an internal fine filter and rotameter. Regulate sample pressure and flow externally; the catalogue recommends about 1 LPM and a sample pressure of 2 to 10 psig.
Take gas samples after the main exchanger where possible and keep sample lines short and clean.
Use an SV-200 vaporiser for liquid draws.

ACCURRA-S sample specification: non-corrosive, non-toxic, non-flammable, non-condensing and dry, free from entrained oil; sample pressure 2 to 10 psig, regulated externally; flow about 1 LPM; dust below 3 micron. Where your sample differs, we design conditioning around it.

Send us your process data

Application data sheet

The same pre-order design inputs our engineers design from, online. Fill in what you know, leave the rest. Your draft saves as you go, and you can print or send it when ready.

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What the data sheet asks for

Send what you have and we will ask for the rest.

The gases to measure, the range, and the accuracy you need
Background gases and their typical composition
Sample temperature, pressure and dew point at the tapping point
Dust level, and whether the gas carries tar, oil or condensable vapour
Process connection and, for ducts, the duct diameter
Where the sample vents to, and at what pressure
Area classification of the tapping point and of the analyser location, and the IP protection needed
Distance between the tapping point and the analyser
Outputs you need: 4-20 mA, dual range, relays, Modbus RTU
Calibration approach, calibration gas available, and whether blowback is required
Utilities at site: power supply, instrument air, nitrogen, steam and cooling water, and the ambient temperature range
Sample pressure at the tapping point and whether the sample is gas or liquid

Recommended Sarvesh products

ACCURRA-S 3090

Oxygen purity models 3090 and 3190 with compensation.

View ACCURRA-S 3090

ACCURRA-S

Trace oxygen and dew point on the same panel.

View ACCURRA-S

SV-200 / SV-400 vaporisers

SV-200 for cryogenic liquid draws.

View SV-200 / SV-400 vaporisers

ACCURRA-TCD

Helium and argon purity.

View ACCURRA-TCD

Frequently asked questions

How accurate is the ACCURRA-S 3090 on 99.5 % oxygen?

The catalogue figure is a compensated error below 0.5 percent, against up to 10 percent uncompensated over a day and night pressure swing. Ask for a calibration plan against your reference gas.

What is the difference between 3090 and 3190?

Both are compensated purity models: 3090 is electrochemical over 0 to 100 percent, 3190 is paramagnetic over 95 to 100 percent. 3190 uses a paramagnetic sensor. Neither has an internal sample pump.

Can one analyser check purity and trace impurities?

Purity and trace are different sensors. Plants usually place a purity analyser on the oxygen line and trace oxygen or dew point analysers on nitrogen and argon.

Do I need to compensate for altitude?

The compensation is automatic and uses the analyser's own ambient pressure reading, so the same unit works at different sites.

Oxygen purity analyser for air separation, PSA and VPSA plants