Which oxygen analyser does HTM 02-01 ask for in PSA plants?

HTM 02-01 (2026), the NHS England guidance, asks for a duplex calibrated paramagnetic oxygen monitoring system with two oxygen analysers.

Does a zirconia sensor need a reference?

Yes. Dietrich, Kusnezoff and Michaelis (Sensors, 2021) note that one electrode must provide a sufficiently stable reference potential for a reproducible measurement of oxygen partial pressure.

Zirconia vs paramagnetic oxygen analysers

Q: Zirconia vs paramagnetic oxygen analysers

A 2021 Sensors article describes potentiometric zirconia oxygen sensors as a zirconia solid electrolyte whose Nernst voltage measures the oxygen partial pressure difference against a reference electrode, while a 2013 Indian Journal of Anaesthesia review describes paramagnetic analysers, which rely on oxygen molecules being attracted into a magnetic field.

How each measures oxygen

	Zirconia	Paramagnetic
Physical principle	An oxygen-ion-conducting zirconia solid electrolyte couples two electrodes, often platinum or platinum-based cermets (Dietrich, Kusnezoff and Michaelis, Sensors, 2021)	Oxygen molecules have unpaired electrons in the outer electron ring, which makes oxygen paramagnetic and attracted into a magnetic field (Garg and Gupta, Indian Journal of Anaesthesia, 2013)
What the signal represents	The Nernst voltage, a measure of the oxygen partial pressure difference between the two electrodes; one electrode must provide a stable reference potential	In newer designs, the pressure difference across a transducer between a sampling chamber and a room-air reference chamber, proportional to the oxygen partial pressure difference

Dietrich, Kusnezoff and Michaelis note that potentiometric zirconia sensors have been widely used for more than four decades to determine oxygen content in automotive applications and industrial processes, and describe the sensor operating at a sufficiently high temperature of 350 to 950 °C.

Garg and Gupta, reviewing gas analysis in anaesthesia workstations, describe older paramagnetic analysers with a dumb-bell and torsion wire system and newer ones with an electromagnet switched at approximately 110 Hz. They call them accurate and highly sensitive, with a rapid response that allows measurement on a breath-to-breath basis, and note that they need scheduled calibrations and a water trap, because water vapour could affect the analysis.

What guidance specifies

HTM 02-01 (2026), the NHS England guidance, asks for a PSA plant to include a duplex calibrated paramagnetic oxygen monitoring system: two oxygen analysers, two oxygen concentration indicators, two oxygen flow monitors and an oxygen concentration and flow recorder. In quality control testing it names the paramagnetic analyser as the specified instrument for the identity of oxygen.
The WHO-UNICEF technical specifications and guidance for oxygen therapy devices (14 January 2019) describe oxygen analysers based on one of several technologies, including the paramagnetic properties of oxygen and zirconia oxygen electrolytic cells, which can usually measure from 0 to 100%.
The International Pharmacopoeia (13th edition, 2025) states that the oxygen content of Oxygen 93% is continuously monitored during production.

In Ultra Controlo equipment

The QuPHARM wall-mounted medical gas purity analyser, launched by Ultra Controlo on 29 May 2026 for medical oxygen generation systems, measures O2, CO and CO2 concentrations simultaneously and is offered with either a zirconia or a paramagnetic O2 sensor. See how oxygen purity is measured in a PSA plant.