At 11:54 PM 6/22/2011, Mark Iverson wrote:
Abd wrote:
"Basically, the device does some math for you, based on certain
assumptions. Unfortunately, the
assumptions are the very issue here!"
I don't' think that's correct... Not assumptions.
The instrument does calculations based on scientific laws and uses
what measured variables it does
have to calculate different units... For example, Relative humidity
is calculated from Absolute
humidity and temperature and pressure. The instrument, if it has the
right probe, is measuring
atmospheric pressure, temperature and at least 3 or 4 other
variables. It then provides the
convenience of displaying other units, like mixing ratio, based on
the actual measured variables and
specific scientific laws (mathematical equations). I have never
seen an instrument that bases the
display of other units on assumptions. I certainly wouldn't buy one!
The instrument does not give "mixing ratio" as a displayed value, as
far as I've seen.
It displays g/m^3, but grams of what? Looks to me like this is grams
of water vapor per cubic meter, which can be calculated from RH at a
given temperature and pressure. That is not the "mixing ratio" of
interest, which would be grams of liquid water per kilogram of steam.
It gives, however, if designed to do that (I think it may be an
option), grams of water vapor per kilogram of gas, on an assumption
that the gas is air or water, i.e., air/water vapor mixed.
The meter is not accurate above 98% RH, apparently, at least the
accuracy is not guaranteed.
