# How can the actual output of a PSA plant be measured?

**How can a technician measure the actual oxygen output of a PSA plant against its rated capacity?**

The Global Fund commissioning guideline (August 2024) checks a PSA plant's real output by running it for at least 24 hours at its rated maximum flow, recording the flow and confirming that purity stays above 90%; it says a reading from an air flow meter instead of an oxygen meter must be multiplied by 1.17.

The Global Fund briefing note on PSA plant oxygen purity (2024) says that as more oxygen is demanded from a PSA plant, the purity will decrease, and the USAID RISE operating procedure (March 2022), written for hospitals in India, warns that drawing more than the plant's capacity drops both purity and pressure. AIGA 113/20, adopted from EIGA Doc 195, includes in the performance qualification, as a minimum, the capability of each supply source to supply the correct oxygen concentration at different flow rates up to the maximum design flow rate. See [why purity drops when demand rises](https://library.ultracontrolo.com/answers/why-does-psa-purity-drop-when-demand-rises/).

## The flow and purity test

The commissioning guideline written by Build Health International for the Global Fund (28 August 2024) sets the minimum test:

- Run the plant uninterrupted for a minimum of 24 hours, with 3 days recommended in its checklist, at the rated maximum flow rate of the system.
- Record the constant flow rate during the test in Nm³/h, if a flow meter is present; if the flow is measured with an air flow meter instead of an oxygen meter, multiply the reading by 1.17.
- Note whether purity drops below the plant's minimum tolerance, given in the checklist as 93 ± 3%; the guideline expects purity to remain above 90% at all times.
- Confirm the on-screen purity with a recently calibrated handheld analyser, directly at the oxygen tank outlet, at bedside outlets where available, and from a recently filled cylinder where filling manifolds are present.
- Record the minimum, maximum and equalisation pressures of both sieve beds.

Capacity figures depend on their reference conditions: WHO's Foundations of medical oxygen systems (2023) notes that the measurement units used determine the actual gas volume produced. See [what rated capacity at normal conditions means](https://library.ultracontrolo.com/answers/what-does-rated-capacity-at-normal-conditions-mean/).

## Instruments and records

- Plant display: WHO's technical specifications for health facility oxygen systems (December 2024) ask the control panel to show product purity at all times and, as optional and recommended, the flow in Nm³/h, with cumulative flow in Nm³ on the automatic purge kit display panel, where applicable, and a data export function such as a USB port.
- Flow meter: Open Critical Care describes, for PSA plants that supply a facility directly by pipeline, recording the flow with a mass flow meter. NHS England's HTM 02-01 (2026) says a PSA plant should include a duplex calibrated paramagnetic oxygen monitoring system with two oxygen analysers, two oxygen concentration indicators, two oxygen flow monitors and an oxygen concentration/flow recorder.
- Daily production: Global Fund sustainability guidance (August 2024) asks for daily production to be recorded, separating oxygen sent directly to the pipeline from oxygen used to refill cylinders; see [how to measure hospital oxygen consumption](https://library.ultracontrolo.com/answers/how-to-measure-hospital-oxygen-consumption/).

## Booster compressor output

For cylinder filling, the Global Fund commissioning guideline (28 August 2024) confirms that the cylinder filling rate is within 10% of the output rate the manufacturer states; Build Health International expects this to be measured on a full manifold, by timing the whole fill and taking the average time per cylinder.

## In ULTRAOX plants

According to the ULTRAOX Technical Data Sheet (2022), an oxygen flow control system installed on every ULTRACON concentrator measures the instantaneous flow of oxygen to the network and shows total oxygen consumption on the digital screen, and the touch screen displays oxygen flow in L/min and total oxygen flow in m³.

### How long should an output test run?

The Global Fund commissioning checklist (August 2024) asks for at least 24 hours of uninterrupted running at the system's maximum flow, and recommends 3 days.

### Can an air flow meter be used on the oxygen line?

The Global Fund checklist says that if the flow is measured with an air flow meter instead of an oxygen meter, the reading must be multiplied by 1.17.

## Sources

- [Global Fund / Build Health International, Overview: PSA Oxygen Plant Commissioning Guidelines (28 August 2024), with appendix checklist](https://resources.theglobalfund.org/media/qp3h1vxo/cr_c19rm-psa-oxygen-plant-commissioning_overview_en.pdf)
- [Global Fund / Build Health International, Briefing Note: PSA Plant Oxygen Purity (3 April 2024)](https://resources.theglobalfund.org/media/lenpqaoa/cr_c19rm-psa-oxygen-purity_technical-briefing-note_en.pdf)
- [USAID RISE, Standard Operating Procedures: PSA Plant Operations and Preventive Maintenance by the Facility Management (March 2022)](https://media.path.org/documents/SOP_on_PSA_Plant_USAID_RISE_04032022_F7fUBr6.pdf)
- [AIGA 113/20 (adopted from EIGA Doc 195), On site generation of oxygen 93% for medicinal use, section 8.4](https://asiaiga.org/uploaded_docs/en_AIGA_113_20_Generation_of_Oxygen_93_for_Medicinal_Use.pdf)
- [WHO, Foundations of medical oxygen systems (17 February 2023), section 2.1](https://iris.who.int/server/api/core/bitstreams/4ad6f5fd-089e-4142-8439-b64e98d816d8/content)
- [WHO, Technical specifications for health facility based medical oxygen systems (31 December 2024), section 1.1, lines 20 and 21](https://iris.who.int/server/api/core/bitstreams/ff437601-add3-44c8-8149-b85f0cdb2b52/content)
- [Open Critical Care, Oxygen FAQ: How do I know how much oxygen my facility is using or needs?](https://opencriticalcare.org/faq/how-do-i-know-how-much-oxygen-my-facility-is-using-or-needs/)
- [NHS England, HTM 02-01 Part A (2026), paragraph 6.121](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)
- [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)
- [ULTRAOX Technical Data Sheet 2022, p. 14 and p. 16](https://www.ultracontrolo.com/products/ultraox)

Reviewed: 2026-10-23. Ultra Controlo engineering. https://library.ultracontrolo.com/answers/how-to-measure-the-actual-output-of-a-psa-plant/