The US EPA defines calibration as: “The comparison of a measurement with a standard or instrument of higher accuracy to detect and quantify inaccuracies and to report or eliminate those inaccuracies by adjustment."
Calibration by comparison to a gas standard
You can calibrate your Aeroqual monitor by comparing the response of it to a gas standard which usually comes in the form of a certified gas cylinder or zero air or ozone generator.
An Aeroqual monitor with gas modules requires a two-point calibration:
- a zero or baseline calibration point with clean air, and
- a single span point at a suitable calibration point.
The zero calibration point is performed simultaneously for all gas sensors and takes approximately 40 minutes to complete.
A controlled flow of zero air is delivered to the monitor via the gas inlet. Zero air can come from a cylinder of certified zero air from a reputable gas supplier, or by filtering ambient air with the appropriate combination of filter media to remove contaminants (e.g. a zero air generator). The AirCal 1000 and AirCal 8000 both include a zero air generator. All gas modules can be zero calibrated using the same source of zero air.
Span gas is delivered for each gas module separately. Span calibration takes approximately 30 minutes per gas module.
Span calibration ensures your monitor reading is accurate to a known concentration of target gas. A controlled flow of span gas can be achieved by:
- obtaining a certified cylinder of calibration gas at the target concentration (the direct method), or
- obtaining a certified cylinder of calibration gas at higher concentration then using a gas dilution calibrator (e.g. the AirCal 1000) to dilute to the target concentration (the dilution method). After the sensor response to the span gas has stabilized (15 to 30 minutes) the gain and offset parameters are adjusted so the monitor reading corresponds with the span gas concentration.
Note: If you’re using the direct method, you need a fixed flow regulator. If you’re using the dilution method, you need a pressure regulator.
You can use Aeroqual Connect or Aeroqual Cloud to make offset and gain adjustments during the calibration process.
Calibration by comparison to other instruments
You can calibrate your Aeroqual monitor by co-locating it alongside a reference monitoring station of higher accuracy. Measurements from the reference instrument are compared to measurements from the Aeroqual monitor. A correlation plot is used to generate offset and gain values which are then applied to your Aeroqual monitor.
All sensors provided to Aeroqual from third-party manufacturers come with a factory calibration. The method and frequency of calibration can be found in the appropriate accessory manufacturer’s user guide supplied with your Aeroqual monitor.