Digital Ventilated Psychrometer

A digital ventilated psychrometer for direct reading of the relative humidity (RH) from the digital indicator by means of two identical type thermistors is described. The method is based on the temperature to linear voltage converter, the calculator of the dry and wet bulb temperature ratio, the converter from the ratio to the voltage proportional to RH, and the analog to digital (A/D) converter. The experimental result by the digital ventilated psychrometer shows that the apparatus makes the direct indication of RH possible. The accuracy of the apparatus is estimated to contain an RH error of less than 2 percent and it is almost the same as that of the Assmann psychrometer. The principal advantage of the apparatus is the direct indication of RH and the capability to use the data directly for the input of the digital data processor.