20
ObservAir
Operating Manual
k.
LEDmode:
Pollution concentration data displayed using the LED
button in breathing mode. The LED can also be set to display only
sensor alerts, or be turned off completely. Options are ‘BC’, ‘GAS1’,
‘GAS2’, ’ALERT’, or ‘OFF’. Default setting is ‘BC’.
l.
LEDra:
Running average, in seconds, applied to the pollution
concentration data displayed using the LED button. Lower running
average values provide higher time resolution but the LED color
display may fluctuate due to sensor noise, while higher running
average values provide a smoother display with lower time
resolution. Default setting is 90 seconds.
m.
LEDmaxConc:
Maximum concentration setting for the LED display.
Default is 5
µ
g/m
3
of BC (default LEDmode setting).
n.
LEDtimeout:
The time duration, in minutes, before which the LED
display turns off automatically. Default is 20 minutes.
o.
maxATN:
Maximum optical attenuation (ATN). When filter loading
is above this value, an alarm is triggered. Default is 80.
p.
timeZone:
Time zone in hours relative to GMT. For example, New
York is represented by “-4” (GMT- 4:00). Default is 0.
q.
GPS:
Optional GPS unit is logging when ‘True’ and powered off
when ‘False’. Default is ‘False’.
3.
Factors:
This
field
contains
calibration
and
environmental
compensation factors for each pollutant species monitored onboard the
ObservAir unit. Most factors in this field are for DST’s internal protocols,
but those pertinent to the end user are listed below:
a.
MAC:
Mass absorption coefficient for BC determination (see
Section 1.1.1). Default value is 12.5 m
2
/g.
b.
FRcal:
Flow rate calibration factor. Default value is 1.0.
c.
Code1:
Calibration code for the first optional gas sensor in units of
nA/ppm. Each gas sensing cell has a unique code from the
manufacturer (see Section 1.1.2).
d.
Code2:
Calibration code for the second optional gas sensor
(nA/ppm).
4.
colNames:
Names of the fields logged in the data file as they appear
on each line. For the base unit ObservAir, without gas sensing, the
following column names will be listed
a.
TS:
Timestamp in the format: YYYY-MM-DD HH:MM:SS
b.
Iref:
Reference intensity from the aerosol absorption photometer.
Value is expressed in terms of the ADC’s raw count. Full scale value
is 8388607.
21
ObservAir
®
Operating Manual
c.
Isig:
Signal intensity from the aerosol absorption photometer. Value
is expressed in terms of the ADC’s raw count. Full scale value is
8388607.
d.
ATN:
Optical attenuation (unitless)
e.
BC:
Black carbon in
µ
g/m
3
f.
T:
Temperature in ºC.
g.
RH:
Relative humidity in %.
h.
FR:
Sample flow rate in ccm.
i.
VBAT:
Battery voltage in volts.
If the unit has a single gas sensor onboard, the following columns will
be appended to those above:
a.
GAS1:
Gas concentration in ppm (except for NO
2
, which is in ppb).
b.
Vg_ref1:
Reference output from electrochemical cell in volts.
c.
Vg_sig1:
Signal output from electrochemical cell in volts.
If the unit has two gas sensors onboard, the following columns will be
appended to those above:
a.
GAS2:
Gas concentration in ppm (except for NO
2
, which is in ppb).
b.
Vg_ref2:
Reference output from electrochemical cell in volts.
c.
Vg_sig2:
Signal output from electrochemical cell in volts.
3.5.2.
Data file
The ObservAir data is written in comma separated value (csv) format to a
.txt file. Each line in the file represents a datalogging event, and starts with
the character “$”. Values are listed in the order provided in the colNames
field of the corresponding setting entry. Typical data output from a base
model ObservAir (without gas sensing) is shown below. If gas sensors are
fitted to the unit, the output data will be appended to each line in the order
listed in the colNames field.
$2020-09-15 23:21:26, 6889274, 7486915, 0.4477415,-0.5281, 37.70047, 32.93088, 99.6, 7.66
$2020-09-15 23:21:28, 6889416, 7487140, 0.4477730, 0.0924, 37.63485, 32.93088, 100.3, 7.66
$2020-09-15 23:21:30, 6889638, 7487262, 0.4473400, -1.2549, 37.52956, 32.91753, 100.3, 7.66
$2020-09-15 23:21:32, 6889808, 7487379, 0.4477415, 1.1772, 37.58144, 32.91753, 100.3, 7.66
$2020-09-15 23:21:34, 6890005, 7487519, 0.4491062, 4.0048, 37.62112, 32.93088, 100.3, 7.66
$2020-09-15 23:21:36, 6890185, 7487705, 0.4500246, 2.6575, 37.72641, 32.93088, 100.3, 7.66
$2020-09-15 23:21:38, 6890353, 7487792, 0.4502516, 0.6841, 37.72336, 32.91753, 100.3, 7.66
$2020-09-15 23:21:40, 6890537, 7488002, 0.4504004, 0.4360, 37.73556, 32.90417, 100.3, 7.66
$2020-09-15 23:21:42, 6890700, 7488091, 0.4514685, 3.1003, 37.69894, 32.91753, 100.3, 7.66
$2020-09-15 23:21:44, 6890863, 7488192, 0.4526644, 3.5079, 37.72641, 32.93088, 100.3, 7.66
$2020-09-15 23:21:46, 6891009, 7488308, 0.4539852, 3.8455, 37.76455, 32.94423, 100.9, 7.66
$2020-09-15 23:21:48, 6891181, 7488379, 0.4539719, -0.0397, 37.71267, 32.91753, 99.6, 7.66
$2020-09-15 23:21:50, 6891322, 7488435, 0.4555502, 4.6042, 37.64859, 32.93088, 100.3, 7.66
$2020-09-15 23:21:52, 6891469, 7488522, 0.4567795, 3.5648, 37.67300, 32.93088, 100.3, 7.66
$2020-09-15 23:21:54, 6891617, 7488534, 0.4580860, 3.7495, 37.66232, 32.93088, 100.3, 7.66