Design Of Controling Box Of Constant Temperature And Humidity

The designs of the software and hardware of the constant temperature and humidity controling box and the PID control arithmetic are primarily discussed in the paper. The controlling box collects the temperature and the humidity of the experiment box and the temperature of the water tank with platinum resistance transducer that has three paths. Then they are sent to the microprocessor 89 C55 to dispose by A/ D and sent to the D/ A to be an 4 ~ 20 mA output of simulant value. At the same time, the outputs of six paths switch quantity drive respectively the relaies of heightening temperature reducing temperature alarm and so on. The system can realize the dialogue both the body and machine with the keyboard and LCD. At last the miniature printer prints the expectant temperature humidity,actual temperature humidity of workroom.and printing times .The system adopts PID control arithmetic and its controling precision achieves 0.2 degrees. It is used for controlling the boxes which volumes are 10 cubic meters and 80 cubic meters and runs well in 24 hours.