I wonder if any one has come across a quick and dirty way of
calculating dew point.

 All the meteorological websites I've been to, offer formulae with
high precision resolution, something I don't think I really need. I'm
also trying not to use floating point maths. The main sticking point
is the log10 function all the other constants I can convert to whole
numbers.

I'm using the SHT11 sensor from Sensirion and have solved the
temperature and RH maths, just the dew point is causing me problems.

Sensirion's and others offer the following formula

logEx = 0.66077+(7.5 * t_C) / (237.3 + t_C) + (log (RH) -2)

DewPoint = (logEx - 0.66077) * 237.3 / (0.66077 + 7.5 - logEx)

Where t_C = temperature in celsius
             RH = true relative humidity

I'm hoping to make this into a greenhouse controller, so I assume
that the frost point would need to be known - gardening ain't my
thing :)

Colin




--
cdb, cdb@barnard.name on 31/03/2002

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