At VisiblAir, we are committed to delivering high-quality, accurate air quality sensors. Each sensor undergoes testing and calibration verification prior to shipping. This document outlines our calibration procedures and the measures taken to ensure the reliability of your VisiblAir device.
1. Particulate Matter (PM) Sensors
Models used: Sensirion (SPS-series, SEN-series) or Piera IPS-7100
Calibration: Factory-calibrated
VisiblAir does not alter the factory calibration of PM sensors. These sensors are calibrated by their respective manufacturers using specialized equipment under controlled conditions.
To ensure proper operation, each unit undergoes a quality check where its PM2.5 values are compared to a Temtop M2000C monitor under ambient air conditions. This confirms the sensor behaves within expected tolerance for real-world use.
2. CO₂ Sensor Calibration
Technology: NDIR (Non-Dispersive Infrared), dual-beam or photoacoustic
Calibration method: Free-air calibration or reference alignment
Setpoint: 415 ppm
Acceptable deviation: ±60 ppm from reference sensor
2.1 Outdoor “Free-Air” Calibration (Preferred Method)
When weather permits, sensors are calibrated using outdoor ambient air:
- The sensor is powered on and placed outside for at least 10 minutes to acclimate.
- Location must be at least 6 feet (2 meters) away from people, cars, buildings, windows, or other sources of CO₂.
- A forced calibration is initiated with a setpoint of 415 ppm.
- Sensor readings are compared to two calibrated reference sensors.
- If within ±60 ppm of both references, the calibration is accepted.
- Otherwise, the procedure is repeated.
2.2 Indoor Calibration Using Reference Sensor
When outdoor calibration is not feasible (e.g., during winter):
- Calibration is performed indoors next to a previously calibrated reference sensor.
- The reference must read below 2000 ppm to avoid saturation or interference.
- The new sensor is forced to calibrate using the reference sensor’s current value.
- If the calibrated sensor reads within ±60 ppm of the reference, it is accepted; otherwise, the process is repeated.
3. Environmental Sensors (Temperature, Humidity, Barometric Pressure, Wind,...)
These sensors are not user-calibrated. During final QA, their values are reviewed for consistency and reasonable behavior under normal room conditions. Any sensor reporting clearly abnormal values is flagged and re-tested or replaced.
4. VOC and NOx Index Sensors
VOC and NOx readings are presented as 24-hour rolling indexes based on sensor response algorithms. As such:
- Real-time calibration is not feasible.
- No absolute reference value is available.
- Units are monitored for stability and pattern consistency over time.
5. CO₂ Calibration Best Practices
- Optical CO₂ sensors are sensitive to shock or vibration, which can affect calibration. If you suspect your unit has lost its calibration—for example, after a drop or impact—a free-air recalibration is strongly recommended.
- Indoor miscalibration risk: It is not possible to detect if a user has incorrectly performed a CO₂ calibration indoors when CO₂ levels were elevated. If such a calibration was performed in an enclosed or occupied space, the sensor may display incorrect values. A recalibration in proper outdoor conditions is required in such cases.
- Routine verification: We recommend performing a CO₂ calibration check every 6 to 9 months:
- Place the sensor outdoors, at least 6 feet away from people, windows, doors, or vehicles.
- Let it stabilize for 5–10 minutes.
- If the CO₂ value is outside the 400–450 ppm range, a calibration should be performed.
6. Certification
Each VisiblAir sensor undergoes testing and calibration in accordance with this procedure. Units that fail to meet our internal verification thresholds are recalibrated or excluded from final packaging.
Upon request, a calibration certificate may be issued with the following information:
- Date of shipping
- CO2 calibration method used
- Sensor UUID
- Sensor model
- Technician ID or initials
- Acceptance result
