AN607

30

Rev. 1.7

Linearization

The above equation is still too complex to be useful in simple systems; however, it can be noted that, over a narrow

temperature range, the relative humidity error is fairly linear with relative humidity for a given amount of heating and

ambient temperature.

The error is linear with RH and increases by about 5% RH per °C (this is the familiar “Mark Lawrence Rule of

Thumb”).

Thus, the actual RH can be estimated fairly accurately by:

The accuracy of this estimate can be improved by measuring the temperature of the RH sensor and correcting for

heating to get the ambient temperature.

For 5 °C heating, the correction factor varies from 0.0598 at 0 °C to 0.0435 at 50 °C ambient or

and finally,

 

RH

RH

measured

10.05

T

–



---------------------------------

=

T

ambient

T

measured

T

–

=

CF

0.0598

0.000346

–

T

ambient



=

RH

RH

measured

1CF

–

T





------------------------------------

=