Measurement equipment
- Breathing machine: Respironics CA-3200
- CO2 sensors: GSS SprintIR-WF-20
- CO2 flow meter ABB PurgeMaster FP-1/4-41-G-3/37
- Pressure sensor: Sensirion SDP816-500PA
- Data aquisition: Arduino Mega
Validation targets
- CO2 measurement
- Cycles and volume flow
Validation strategy
Carbon dioxide concentration
- Volume flow over sensors: Pressure differential over CO2 sensing loops are measured as well as the flow through the sensing loop.
- Adding dead volume: Dead volume is added to the system in the form of 32mm PVC piping.
Pressure drop over mask
- Volume flow: Outlet is blocked by mask
Validation test data
Volume flow over sensors
| Sensor | Pressure drop inhale | Pressure drop exhale | Flow inhale | Flow exhale |
| Exhale sensor | ~0 Pa | 1000 Pa | ~0 L/min | 5.8 L/min |
| Inhale sensor | 2750 Pa | ~0 Pa | 11.5 L/min | ~0 L/min |
Known dead volumes
| Dead volume | CO2 Exhale | CO2 Inhale | Theoretical |
| 0.04 | 5.06% | 0.12% | 0.10% |
| 0.20 | 5.10% | 0.48% | 0.51% |
| 0.33 | 5.20% | 0.86% | 0.87% |
Volume flow under pressure drop over mask
Tested masks
| Masker nr | Name | Inhale CO2 concentration [%] | Exhale CO2 concentration [%] | Inhale volume [L] |
| 16 | 3M 8320 | 0.91 | 5.24 | 2.07 |
| 25 | BIZTEX NIOSH N95 | 0.66 | 5.22 | 2.10 |
| 27 | VWR 113-0645 | 0.87 | 5.40 | 2.07 |
| 20 | Dräger Piccola VRAD-F028 | 0.93 | 5.39 | 2.09 |
| 26 | 3M Aura 1883+ | 0.90 | 5.32 | 2.05 |
| 30 | Starchem PADM-10V | 0.58 | 5.25 | 2.06 |
| 19 | UQ 509/68 | 0.73 | 5.24 | 2.05 |
Conclusion
- Pressure drop and flow over sensors show that the corresponding sensors are only experiencing a volume flow under inhalation and exhalation
- The large pressure drop over the sensors ensures a large volume flow and a short response time.
- Dead volume test shows direct correlation between the added dead volume and the measured CO2 concentration in the inhaled air
- The CO2 concentration in the inhaled air corresponds with the theorized increase by adding dead volume
- Inhale volume and exhale CO2 concentration is within +- 5% of the desired value of 2L and 5%.
- Inhale CO2 concentration without mask is higher than the ambient CO2 concentration (0.04%), this can be explained by rebreathing of the exhaled air around the dummy head. (This was also verified by elongation of the inhalation CO2 measuring tube beyond the head)
- The inhale CO2 concentration is for all masks below 1% as is expected from masks certified according to NEN 149 norm.