Multichannel digital ventilated psychrometer using eight-bit microcomputer

A multichannel digital ventilated psychrometer using an 8-bit microcomputer has been developed. It offers the advantages of direct reading of the relative humidity (RH) and the temperature from the digital indicator (or the CRT indicator) as well as multichannel use. The sensing of humidity is based on the psychrometric principle by two integrated circuit (IC) temperature transducers acting as dry and wet bulbs. The temperature of the dry bulb has a range of 0-50°C with a linearity better than 0.05°C. The temperatures of the dry and wet bulbs are converted into proportional voltages which are fed into a microcomputer after having been converted into digital form by the A/D converter. As the RH data for dry-bulb temperature and dry- and wet-bulb temperature difference have previously been stored in the memory, the corresponding RH data can be derived from using the necessary steps of the program. The results are displayed on a digital indicator. The indication shows the channel number being measured, the RH, and the dry-bulb temperature. The experimental results show that it is possible to make an apparatus to give a direct indication of RH for the multiple sensors and the accuracy of the apparatus is estimated to contain an RH error of less than 2 percent with a response time of less than 20 s. It may be used both for measurement and control of a multiple humidity environment.