DST ObservAir Manual de instrucciones - Página 19

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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,

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.

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

including

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

Slow

Yellow

Fast

Yellow

Very Fast

Yellow

Slow

Red

Fast

Red

Very Fast

Red

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.

Error

High

Replace filter.

attenuation

Check that SD card is properly

SD card

inserted. Take SD card out fully

error

and re-insert into the slot.

Reset time according to the

Clock error

instruction in Section 3.6.3.

Check that filter is properly

LED error

seated. Replace with new filter.

Flow rate

Check that nozzles and sample

error

lines are unobstructed.

Critical

Contact DST Technical Support.

error

Table 10. LED error code lookup table.

ObservAir

Operating Manual

Solution