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Calibrating the LI-7000 for H2O

To calibrate the LI-7000 CO2/H2O Analyzer for water vapor, LI-COR recommends using our LI-610 Dew Point Generator. The LI-610 generates a known water vapor concentration and reports the dew point value on the front LCD display in units of Degrees C. The gas stream can then be plumbed directly into the LI-7000's appropriate inlet port. If using the LI-7000 Windows Interface Software, it is very simple to enter this value directly into the software, choose the correct units, and continue on with either the zero or span calibration.

If using the LI-7000 Instrument Software through the LI-7000 keypad and display, there can be a units conversion issue that is easy to resolve. Notice in the picture below that the water vapor value is requested in units of mmol/mol (displayed as "mm/m").

Since the LI-610 output is in degrees C, you would need to perform some calculations to convert the units; however, there is a much easier solution.

Use the LI-7000 keypad to access the Ref/Cal group. Press the [Shift] key and then the [1] key. Next, press the [f1] button below the screen labeled, "SetRef...". A new window will open. This is where you tell the LI-7000 what gas stream will be used in the Reference Cell (A). Notice that the units beside the H2O can be edited.

Use the arrow keys to move the cursor to the H2O units. Once that block has been selected, press the [f1] key labeled "Edit...". This will toggle the units for water between °C and mmol/mol. Select "°C" and then press (f5) "OK".

Return to the Calibration group. Now, when prompted to enter an "Exact value..." for the H2O, the units listed will be in degrees C. You can simply enter the value shown on the LI-610 Dew Point Generator's display.