DST ObservAir - Operational Settings for Common Applications

44
ObservAir Operating Manual
data logging period. The values in the table are calculated according the
procedure presented above. Two illustrative scenarios are also provided.
Data logging period
2 sec
15 sec
1 min
1 hour
Avg. BC
0.5 µg/m
3
N/A
200/3.1
100/6.3
25/25.0
1 µg/m
3
200*/1.6ª
100/3.1
50/6.3
25/12.5
5 µg/m
3
60/1.0
25/2.5
25/2.5
25/2.5
10 µg/m
3
30/1.0
25/1.3
25/1.3
25/1.3
Minimum Flow Rate (ccm)*/ Maximum filter life (days)ª
Table 7. ObservAir’s minimum flow rate setting and maximum filter life
as a function of average BC concentration and data logging period. The
ObservAir cannot provide BC concentration data with a baseline noise
< 0.05 µg/m
3
on 2-second basis, so the top left cell is empty.
• Scenario 1: BC
avg
= 7 ug/m
3
, Logging interval = 2 seconds
For this scenario, the BC baseline noise should be ≤ 0.7 µg/m
3
at 2-second
logging. Using the calculation procedure above, the minimum flow rate
setting is (0.3/0.7)*100 = 43 ccm. For these settings, the maximum filter
life is ~1.7 days. Alternatively, refer to Table 7 and see that for 2-second
measurements of 5 µg/m
3
average concentrations, the flow rate setting is
60 ccm. By interpolation, the flow rate can be set to 60*7/5 = 43 ccm.
• Scenario 2: BC
avg
= 0.35 ug/m
3
, Logging interval = 1 minute
The BC baseline noise should be from ≤ 0.035 µg/m
3
at 1-minute logging.
From Table 1, the noise is 0.05 ug/m
3
at 1-minute and 100 ccm, so the
minimum flow rate is (0.035/0.05)*100 = 70 ccm. In Table 7, a flow rate
of 100 ccm is recommended for 1-minute measurements at 5 µg/m
3
. By
interpolation, the flow rate can be set to 100*0.35/0.5 = 70 ccm. The filter
life can be calculated as 510/(0.35*70) = 20.8 days.
IMPORTANT NOTE: The above considerations do NOT apply to gas
sensing. The gas sensors’ measurement performance remains largely
constant with varying flow rate.
5.4. Operational settings for common applications