Table 1.
Technical specifications of the CO2 measuring devices used in this study.
| NDIR Sensor | OP-Laser | PAS Analyzer | |
|---|---|---|---|
| Operating principle | Non-Dispersive Infra-Red | Tunable Diode Laser Absorption Spectroscopy | Photoacoustic spectroscope |
| Target gas | CO2 only | CO2 only | CO2 and others |
| Tuned wavelength for detection of CO2 (µm) | 4.3 | 1.6 | 14.1 |
| Detection limit | 0.2 ppmv | 2000 ppm∙m | 1.5 ppmv |
| Accuracy | ±30 ppmv ± 2% | 500 ppm∙m | ±1% |
| Response time (T1/e) | 20 s (diffusion time) | 1 s (scan rate) | 25 s (for 1 gas, including flushing period and 5 s sampling integration time) |
| Operating temperature (°C) | 0 to +50 °C | −45 °C to +80 °C | −20 °C to +70 °C |
| Sensitivity to pressure 1 | 0.1% | Not determined | 0.5% |
| Type of calibration | Two-points calibration in the laboratory | Continuous self-calibration mechanism with a reference gas crystal cell | Two-points calibration at factory |
| Laboratory check of calibration with certified gas | Yes | Yes | Yes |
| Cross-compensation for water vapor | Not needed | Not needed | Yes |
| Cost per unit (€) 2 | 300 | 35,000 | 28,000 |
1 Specified by factory; 2 Approximate, excluding costs with external datalogger systems, when applicable.