High-Accuracy Oxygen Flow Meter for the Exploration Portable Life Support System

"The xEMU’s portable life support system (xPLSS) requires a high accuracy instrument to measure the rate of oxygen flow in the ventilation system. The sensor must produce accurate readings across a wide range of flow conditions while consuming very little volume or power and introducing very little pressure loss to the ventilation loop.

We have developed an innovative flow sensor built around a commercial, off-the-shelf MEMS flow-sensing chip that is designed for oxygen service. We have developed a custom flow sensor housing to channel gas flow over the MEMS sensing elements and custom electronics to control the sensor and generate signals compatible with xEMU requirements. The flow sensor operates in parallel with the ventilation loop heat exchanger, so introduces no additional pressure loss to the ventilation system. The unit meets size and shape requirements for service in the xPLSS and is replaceable in space if necessary.

Data from separate-effects tests and tests of the integrated xPLSS heat exchanger / flow meter system show that the flow meter achieves high accuracy requirements across the range of specified operating conditions.

We built and tested a proof-of-feasibility prototype in mid-2019, followed by a “rapid turn” demonstration sensor that meets form, fit and function requirements in late 2019. Fully-qualified DVT units are scheduled for delivery in mid-2020."