extended periods, as this may cause overheating of the internal
components.
For long-term outdoor deployments, the ObservAir should be
housed in the DSTech active ventilation enclosure. It is best to orient the
sensor with the nozzles facing downwards to prevent the aspiration of rain
or moisture.
5.6. Accurate sample flow rate measurements are critical
BC concentrations are inversely proportional to the flow rate of air drawn
through the aerosol filter (see Section 1.1.1), so any flow measurement
errors translate directly to the reported BC. For example, if the ObservAir’s
flow rate measurements are 10% lower than the actual value, BC
concentrations will be overreported by 10%. Given this proportional
relationship, flow rate measurement drift can be post-corrected. In the
example above, all collected BC concentration measurements can simply
be scaled up by 10% to compensate for the flow rate drift.
When BC measurements are consistently offset from those
collected by another ObservAir or reference instrument, miscalibration of
the flow rate sensor is almost always responsible. If BC measurements are
proportionally lower than the reference value, then it is also possible (but
less likely) that the ObservAir is leaking. Given these potential error
modes, it is important to validate/calibrate the flow rate sensor output
and perform leak checks regularly (see Section 4 for instructions). Since
it is not typical for the ObservAir to leak or for the flow rate sensor’s output
to drift significantly, these routine maintenance tasks are often neglected,
and are nearly always the source of BC measurement errors when they do
occur. When properly calibrated, the ObservAir’s flow rate measurements
should be within ±2 ccm of those collected with a primary flow calibrator.
6. Troubleshooting
6.1. LED error codes
The ObservAir constantly runs diagnostic checks to detect and flag
measurement errors and warnings. When an error is detected, the LED
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