What should be done if the IRGASON or EC150 reports negative water vapor concentration?
The EC150 and IRGASON can report a negative water concentration if enough liquid water accumulates on the optical windows. This is because the absorption spectrum of liquid water differs from that of water vapor. Typically, large rain droplets do not cause this phenomenon. Rather, misty or condensing conditions, which create a water film across the entire optical window, can cause this phenomenon. After the water film evaporates, the former measurement accuracy will be restored.
The IRGASON and EC150 may also experience some amount of drift over time. If conditions are relatively dry and it has been a long time since a zero and span has been performed on the analyzer, it is possible to report a negative water vapor concentration. In this situation, perform a zero and span of the analyzer.
How can the IRGASON or EC150 recover more quickly from precipitation, dew, or frost?
The EC150 and IRGASON gas analyzer windows are polished, slanted at an angle, and coated with a hydrophobic material to prevent water from collecting on their surfaces. Wicks may also be used on the windows to promote capillary action and move water away from the window edges. Also, heaters in the snouts may be turned on to help minimize data loss due to precipitation and condensation events.
Can a fine-wire thermocouple be used with the IRGASON or EC150?
Yes. A fine-wire thermocouple, such as a FW05, can be used.
If getting a span gas is difficult, can the analyzer just be zeroed?
For greatest accuracy, Campbell Scientific recommends that a zero and a span be done on the EC150 or IRGASON. However, if a span gas is difficult to obtain, at the minimum, perform a zero on the analyzer. Performing a zero will correct the majority of drift experienced by the analyzer. Follow the zero procedure in the analyzer’s manual for details.
What kind of gases need to be ordered to zero and span an analyzer?
To zero the analyzer of an EC150 or an IRGASON, any gas that is free of CO2 or H2O, such as nitrogen gas, will work. To span CO2, use mixtures of CO2 in air. It is important that air, not pure nitrogen, be used as the balance gas, so that the pressure-broadening characteristics match that of ambient air. Ideally, use a CO2 span gas concentration that is close to the expected concentration that will be measured at the site.