# How often should a PSA plant's oxygen analyser be checked?

**How often should the oxygen analyser of a PSA plant be checked against a handheld analyser?**

Global Fund guidance asks for a daily check: its PSA daily checklist records the purity on the plant's PLC alongside a handheld analyser reading, and its 2024 sustainability guidance asks for purity to be recorded every day with at least two different analysers.

## Check frequencies in the guidance

| When | Check | Source |
|---|---|---|
| Each day the plant runs | Record the purity shown on the PLC and the purity measured with a handheld analyser | Global Fund daily maintenance checklist |
| Daily | Record purity with at least two different analysers; at a minimum, measure it with a handheld analyser | Global Fund sustainability guidance (2024) |
| Daily | Inspect oxygen purity, with the pre-filter, compressor pressure and oil level, tank pressures and dryer dew point | USAID RISE operating procedure, written for hospitals in India |
| At least quarterly | Test the quality of gas from the PSA plant | HTM 02-01 Part B, NHS England (2026) |
| Preferably every six months | Have oxygen samples tested by an accredited laboratory to validate the plant and its oxygen analyser | USAID RISE operating procedure |
| Yearly | Calibrate the oxygen sensor | USAID RISE operating procedure |
| At commissioning | Verify the operation of the oxygen analyser and all alarms | WHO interim technical specifications for PSA plants (2020, superseded by WHO's technical specifications of 31 December 2024) |

## When the readings disagree

The USAID RISE procedure lists a faulty sensor, and a faulty PLC reading that must be calibrated as the manufacturer recommends, among the points to check when purity is low. HTM 02-01 asks for connections for calibration cylinders at the plant, alongside its duplex monitoring system, and PATH and CHAI (2021) include calibrating pressure and oxygen sensors in the preventive maintenance a buyer can contract to the manufacturer. The 2020 WHO interim specification asked for the plant's oxygen concentration monitor to have ±1% accuracy.

As reference points, Global Fund's 2025 guide to expected values treats above 90% as medical grade and says that a reading below 85% should lead to an investigation, while HTM 02-01 isolates a PSA plant from the pipeline below 94%. Open Critical Care says periodic checks need oxygen analysers and suggests asking the manufacturer or authorised distributor for the specific analysers needed for maintenance, and WHO (2023) lists an oxygen analyser in the maintenance toolkit that operators should have.

## Records

Global Fund's checklist asks the technician who completes it to initial the form, and asks for a separate set of records for each system in a duplex or triplex plant.

## Ultra Controlo analysers

Ultra Controlo supplies a portable oxygen purity analyser for on-site checks of oxygen concentration in pipelines and cylinders. On ULTRAOX SC plants, purity is measured by one or two oxygen analysers with a zirconium oxide probe, and the QuPHARM wall-mounted analyser, launched in May 2026, has programmable alarm thresholds on its oxygen, carbon monoxide and carbon dioxide channels.

### Which reading should prompt action?

Global Fund's expected values (2025) say a reading below 85% should lead to an investigation; NHS England's HTM 02-01 isolates the PSA plant from the pipeline below 94%.

### Who keeps the purity records?

Global Fund's checklist asks the technician who completes it to initial each day's form, and asks for a separate set of records for each system of a duplex or triplex plant.

## Sources

- [Global Fund / Build Health International, Daily Maintenance Checklist for PSA plants (Project BOXER)](https://resources.theglobalfund.org/media/xbanfgrc/cr_c19rm-psa-plant-daily-maintenance_checklist_en.pdf)
- [Global Fund / Build Health International, Overview: Sustainability Guidance for PSA Oxygen Plants (22 August 2024)](https://resources.theglobalfund.org/media/bwrp43cm/cr_c19rm-psa-oxygen-plant-sustainability_overview_en.pdf)
- [Global Fund / Build Health International, Valeurs attendues de la liste de vérification quotidienne (5 June 2025, French)](https://resources.theglobalfund.org/media/ge3bodrr/cr_c19rm-oxygen-plant-daily-maintenance-checklist-values_table_fr.pdf)
- [USAID RISE, Standard Operating Procedures: PSA Plant Operations and Preventive Maintenance by the Facility Management](https://media.path.org/documents/SOP_on_PSA_Plant_USAID_RISE_04032022_F7fUBr6.pdf)
- [NHS England, HTM 02-01 Part A (2026), paragraphs 6.121 and 6.122](https://www.england.nhs.uk/wp-content/uploads/2016/05/health-technical-memorandum-02-01-medical-gas-pipeline-systems-part-a-design-installation-validation-verification-aug-2026.pdf)
- [NHS England, HTM 02-01 Part B (2026), paragraph 11.131](https://www.england.nhs.uk/wp-content/uploads/2016/05/health-technical-memorandum-02-01-medical-gas-pipeline-systems-part-b-operational-management-aug-26.pdf)
- [PATH and CHAI, Oxygen Generation and Storage: Pressure/Vacuum Swing Adsorption Plant (July 2021)](https://media.path.org/documents/O2_generation_and_storage_PSA_VSA_v1.pdf)
- [WHO, Technical specifications for Pressure Swing Adsorption (PSA) oxygen plants, interim guidance (8 June 2020)](https://www.who.int/publications/i/item/WHO-2019-nCoV-PSA_Specifications-2020.1)
- [WHO, Foundations of medical oxygen systems (17 February 2023), section 2.2.2](https://www.who.int/publications/i/item/WHO-2019-nCoV-Clinical-Oxygen-2023.1)
- [Open Critical Care, Oxygen FAQ: How can you assess quality of oxygen produced?](https://opencriticalcare.org/faq/how-can-you-assess-quality-of-oxygen-produced/)
- [Ultra Controlo, Portable Oxygen Purity Analyzer](https://www.ultracontrolo.com/accessories/portable-oxygen-analyzer)
- [ULTRAOX SC datasheet, p. 2](https://www.ultracontrolo.com/products/ultraox)
- [Ultra Controlo, QuPHARM product page](https://www.ultracontrolo.com/products/qupharm)
- [WHO, Technical specifications for health facility based medical oxygen systems (31 December 2024), note on the oxygen generator plant specification (supersedes the 2020 interim PSA specifications)](https://iris.who.int/server/api/core/bitstreams/ff437601-add3-44c8-8149-b85f0cdb2b52/content)

Reviewed: 2026-10-22. Ultra Controlo engineering. https://library.ultracontrolo.com/answers/how-often-should-a-psa-oxygen-analyser-be-checked/