9
iGAS Operating Instructions, Issue 6, Apr 2018
APPENDIX
FEATURE FLAGS
(shown as
underlined italics
in the text)
The operation of iGAS is controlled by Feature Flags which may be set or cleared by the operator. They
are normally set automatically by AirQWeb. The basic set of Feature Flags is as follows, preset factory
defaults are shown ticked:
Feature Flag Name
Explanation/Description
iGAS
√
Measure gas concentrations
iEXTRA
√
Measure extras such as NOX, ambient CO2, manifold T,
sample T
iDUST
Measure particle concentrations, iDUST module required
iMET
Measure meteorological conditions, iMET module required
US units
SI units by default
IGAS mass/volume
Express gas concentrations as µg/m^3 instead of ppb
Auto Start
Automatically start sampling whenever power is on and
battery condition is OK
Daily sample
New sample starts at midnight each day, the Auto Start
feature must be on. Will terminate active sample at
midnight.
Timed sample
Each sampling period terminates after a set number of
reports, specified in the Instrument Settings table (IS)
Stop if fault
√
Stops sampling if a fatal fault occurs
Continuous Zero
√
Continually determine sensor zero gas offset. Overrides
Periodic Zero flag. Takes two Zero phases to complete (2
minutes by default).
Periodic Zero
Measure sensor zero gas offset at start of sampling and
thence at the Zeroing interval specified in the instrument
Settings. Takes three Zero phases to complete
Use Period Zero
Apply the zero offset readings determined by the Periodic
Zero above. Over-ridden by the Continuous Zero Flag
Apply offsets
√
Apply the systemic zero offsets, manually entered into SEDs
Use rise times
√
Correct for T90 response time
iDUST Auto Zero
Only If the iDUST module is fitted, measures the zero dust
particle count.
Continuous PID lamp
Power the PID lamp continuously
Circular Buffer
Use circular buffers to record stacked samples, number of
stacked samples saved before overwrite is specified in the
Instrument Settings Table (IS)
Calculate NOX
Calculate NOX=NO2+NO. Sensors must be fitted
Swap Air Filters
Electronically interchanges the chemical air filters, so the
sample filter becomes the zero gas filter and vice-versa
Use iGAS Matrix
√
Correct for gas species interferences. Gas matrix elements
must be defined in SEDs
Age correction
Apply the sensor cell ageing characteristic from SEDs.
Typically -2% per month
Disable CCC
Turn off Carbon Catalysis Compensation measurement
No CCC
D
on’t apply Carbon Catalysis Compensation
