##### Dew Point and Humidity

*Dew point from humidity:*

*Dew point from wet bulb:*

These calculations are based on Vaisala's humidity conversion formulas.

where

*Note that measuring humidity accurately is challenging, especially at high humidities. Even the best
humidity sensors start to over read 1 - 3 % once you get past 90% RH.*

*(P*is calculated: $$P_{ws}=A*10^{\left ( \frac{mT}{T+T_n} \right ) }$$_{ws})*T*is the temperature in deg C, the following are constants valid for a temperature range -20 to +50 deg C with a maximum error of 0.083%;*A*= 6.116441,*m*= 7.591386,*T*= 240.7263 Water vapour pressure itself is then calculated (hPa) using the relative humidity and_{n}*P*: $$P_w = P_{ws} * \frac{RH}{100}$$ Now Dew Point_{ws}*(T*can be calculated: $$T_d = \frac{T_n}{\left [ \frac{m}{^{10}log \left (\frac{P_w}{A} \right )} -1 \right ]}$$ For calculating dew point and humidity from the wet bulb (for a given pressure): $$P_w = P_{ws}(T_{wet})-pressure * K * (T_{dry}-T_{wet})$$_{d})where

*P*= Water vapour pressure,_{w}*K*= Psychrometer constant 0.0008 /deg C. Once*P*is known, humidity and dew point can be calculated using the above equations._{w}