written to the desired value. Then the zero-and-span control setting is set to 3. After the
IRGASON completes the span, the span control setting is written as -3.
ConfigCmd 14
through
17
automatically store the results of the zero-and-span procedure. Each result is a coefficient
used in the gas analyzer’s algorithms for calculating gas concentrations.
10.3.2 ConfigCmd 18 heater voltage
Normally, the
EC100Configure()
instruction is run in the processing task. Skipped scans can
occur when the
EC100Configure()
instruction executes. When changing operational
parameters, these skipped scans are acceptable. However, they may not be acceptable when
changing the heater voltage.
ConfigCmd 218
allows
EC100Configure()
to operate in the
SDM task, thus avoiding skipped scans. When using
ConfigCmd 218
, the command must be a
constant and the instruction cannot be placed in a conditional statement.
The IRGASON includes heaters near the optical windows. This setting gives the voltage applied to
the heater. It can be set to -1 to disable the heater, or set it to any voltage between 0 and 4.0 V.
The heater resistance is 6 ohms, so the heater power (P
H
) expressed as Watts (W) is given by:
The maximum power (at 4.0 V) is 2.4 W.
Operating the heaters following a precipitation event encourages water droplets on the windows
to evaporate more quickly, thus restoring signal strength. Heater usage may also be used to
prevent formation of dew and frost on the windows, which leads to invalid measurements due to
differences in absorption spectra of liquid water and water vapor.
The heaters, however, should be disabled when they are not needed. Heating near the sample
volume may cause air density fluctuations that can affect flux measurements. Disabling the
heaters will also conserve power. Care should be taken to avoid operating the heaters if the
system voltage is too low or if the ambient temperature is > 45 °C. Operation at temperatures >
45 °C will overload the thermoelectric coolers of the detector, as indicated by the TEC Temp
diagnostic flag (see
(p. 48)).
A data logger may be used to dynamically control the heaters by using input from another
moisture sensor such as a leaf-wetness sensor. When the sensor output indicates moisture is
present, the data logger can send the
EC100Configure()
instruction to the IRGASON and
enable the heaters.
IRGASON® Integrated CO
2
/H
2
O Open-Path Gas Analyzer and 3D Sonic Anemometer
52
Summary of Contents for IRGASON
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