36
ObservAir
Operating Manual
5.5.
Indoor/Outdoor monitoring guidelines
The ObservAir can be operated in nearly any indoor environment without
modification: The sensor is plugged into a power source and set to run for
as long as needed. The magnetic cover provides good moisture and dust
protection for more demanding operating environments, including
outdoors, as long as operating limits are not exceeded and direct exposure
to water (rain) is avoided. Exposure to direct sunlight should also be avoided
over extended periods, as this may cause overheating of the internal
components. With the magnetic cover fitted, the sensor cannot be plugged
in to recharge, limiting the deployment time to about 24 hours.
For long-term outdoor deployments, the ObservAir should be
housed in a weatherproof enclosure, such as those provided by DST. It is
best to orient the sensor with the nozzles facing downwards to prevent the
aspiration of rain or moisture. In extreme environments that exceed the
sensor’s operational limits (e.g., freezing conditions), temperature
controlled enclosures should be used. If operating in temperatures below
5˚C, DST offers the heated SubZero™ case: a tough, hermetically sealed
enclosure that is specifically designed for long winter deployments.
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.
37
ObservAir
®
Operating Manual
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
button flashes rapidly until the error is resolved. The color and speed of the
flashing LED indicates the error type, as shown in Table 10 below. Brief
instructions on how to resolve each error type are also provided.
LED Flash Pattern
Error
Solution
Slow
Yellow
High
attenuation
Replace filter.
Fast
Yellow
SD card
error
Check that SD card is properly
inserted. Take SD card out fully
and re-insert into the slot.
Very Fast
Yellow
Clock error
Reset time according to the
instruction in Section 3.6.3.
Slow
Red
LED error
Check that filter is properly
seated. Replace with new filter.
Fast
Red
Flow rate
error
Check that nozzles and sample
lines are unobstructed.
Very Fast
Red
Critical
error
Contact DST Technical Support.
Table 10.
LED error code lookup table.
6.2.
Unresponsive sensor
If the ObservAir becomes unresponsive, the software may have crashed and
a hard reset is required. A hard reset can be triggered by swiping the
magnetic cover over the top of the sensor (Figure 14). A magnetic detector
is located inside the sensor just below the interactive LED button, and will
trigger a hard reset when exposed to the magnets in the cover. When a hard
reset is triggered, the LED will flash green and the sensor will restart into
the normal operating mode. If the sensor becomes unresponsive often or
on a regular basis, please contact DST Technical Support.