The Design Of A Two-degree-of-freedom PID Feedforward Decoupling Control System For A Constant Temperature And Humidity Box

The constant temperature and humidity chamber can produce stable experimental environment which is widely used in the biological,pharmaceutical,chemical,and other industries.The traditional chamber has low control precision,which can't meet the high accuracy requirements of temperature,relative humidity and human-machine interaction required by modern experiments.In this thesis a constant temperature and humidity experimental box control system based on two-degree-of-freedom PID feedforward decoupling control is designed.This control system includes OMRON NX controller,NA touch screen,sensor,temperature control module,humidity control module and wireless communication modules.The NX controller is connected to the NA touch screen through the EtherNet/IP network,and the operation parameters can be changed by touch screen.The two-degree-offreedom PID decoupling algorithm is designed in NX controller to calculate the temperature and humidity control quantity,eliminate the influence of temperature and humidity coupling,and greatly improve the control performance indexes.The NX controller collects the state of the lower field equipment and drive the actuator through the establishment of 485 polling communication network.The communication with the remote server is established through the wireless transmitter,which is convenient for the operator to monitor and change the operation parameters remotely.The work of this topic is mainly focused on the following aspects:(1)The system composition of the constant temperature and humidity experimental box is introduced,the demand analysis of the control system is carried out,and the key technologies used in the control system are introduced.(2)Step response experiment and mechanism method are used to model the controlled system,feedforward decoupling design is adopted to eliminate the coupling effect of temperature and relative humidity,a two-degree-of-freedom PID controller with a target value filter is designed,and Simulink is used for simulation verification,proving the feasibility of the control system design(3)According to the temperature and humidity control technologies,control system hardware is selected and 485 communication networks are set up.The control program of the NX controller is programmed by the Sysmac Studio software,which including signal acquisition,polling flag bit computing,a serial port communication and output control,etc.,NA touch screen human machine interface is developed to simplify this system control,which including user login,temperature and humidity,parameter setting,condition monitoring and alarm log,etc.,The constant temperature and humidity experiment box control system designed by this subject realizes the temperature control precision of ± 0.1?,relative humidity control accuracy ±1%,and can guarantee stable temperature and humidity without fluctuation for a long time running.It has the functions of monitoring and alarm to improve the security and reliability of the system operation.By loading the wireless transmitter to realize the function of remote monitoring,historical data inquiry and log query.