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NCAR / WVD-MCSupdate

Addition of NCAR MCS, rewrite to software infrastructure, and expansion of features for WVD operations.
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Check weather station absolute humidity #255

Closed stillwer closed 1 year ago

stillwer commented 5 years ago

The weather station reports both relative and absolute humidity...or so we have written down. Scott mentioned he thought the absolute humidity might be something of similar value but not the same quantity. So check the Lufft documentation to verify.

stillwer commented 5 years ago

The sensor is currently reading the following data inputs.

160 = Average temperature with units of Celsius 260 = Average relative humidity with units of % 360 = Average absolute air pressure with units of hPa 270 = Average mixing ratio with units of g/kg

It should be reading the following instead of 270 265 = Absolute humidity with units of g/m^3

stillwer commented 5 years ago

Just tried calculating absolute humidity from relative humidity and temperature two ways: 1) Calculated air density using the ideal gas law and used that to convert from mixing ratio to absolute humidity 2) Found an online calculator that looks a whole lot like Clausius-Clapeyron and used that to convert relative humidity and temperature

Both conversions look very similar but are not equal to the number read by the sensor. Today, both calculated absolute humidities were around 5.2 and that read from the sensor is around 6. Need to contact Lufft about that difference.

stillwer commented 5 years ago

Emailed Lufft about this. Will write when I hear back.

stillwer commented 5 years ago

Received a response from Lufft on Oct. 14th, 2019. Requested more info about my calculations. I sent that data on the 16th. Back to waiting.

stillwer commented 5 years ago

I pinged Lufft again this morning. Still haven't heard anything back.

stillwer commented 5 years ago

Lufft seems to have found the problem. Their email to me is as follows:

Hello Mr. Stillwell, please find the answer to your request below and thank you again that you have recognized this problem.

"The observed deviation of the abs. humidity measurement has been caused by a rounding error that has propagated in the calculation. The calculation has been resolved and will be available with the next release of the firmware."