Design Of Controlling System Based On PLC Intelligent Heat Exchanger

In the 20th century,due to the limitations of automatic control technology,many heat source supply equipment used in factories generally used water water heat exchange units.This type of equipment covers a large area,has a large self weight,and accounts for a high proportion of construction capital investment.When the equipment is running,the maintenance personnel monitor the equipment 24 hours,which increases the operation cost of the equipment process.With the continuous improvement of control technology,this operation mode is gradually eliminated.The mechanical part of the system mainly includes plate heat exchanger,water pump,pneumatic valve and water tank;the electrical part mainly includes electrical power transmission system and automatic control system,in which the automatic control system includes PLC controller,touch screen,temperature detector and pressure detector.The key equipment models are determined according to the best calculation method.PID fuzzy control technology is introduced into the structure of the equipment.The traditional PID technology directly uses proportion,integral and differential to control the whole heat exchange process.But in the actual application,integral and differential can not directly use the results.First of all,the PID technology is analyzed,the control process is discretized,and the use of discrete mode brings the increase of workload.Therefore,the incremental PID control scheme is introduced into the control system to improve the system control process.When the seasons change alternately,the incremental scheme can not provide correct data.Finally,the incremental incomplete differential method is introduced for processing.Although the control mode of the system has been greatly improved,the pressure and temperature detection equipment inevitably have a lag phenomenon in operation.In order to reduce the impact of the lag phenomenon,the Smith prediction scheme is adopted in the system operation,but the sensitivity is reduced due to improper prediction.Then,the fuzzy control technology is added to the Simth prediction scheme to improve the response speed,avoid overshoot and improve the operation accuracy of the equipment.After the system PID control mode is determined,the actual PLC programming process is determined,and the CPU,input module and output module are assembled according to the selected PLC control equipment.Then according to the intelligent heat exchange unit control process,circulating water pump operation process,temperature control process and make-up water pump operation process,the PLC control process program is compiled.The main program compiled on the basis of SIEMENS S7-200 smart PLC consists of the boot test program,the PID differential pressure program for the inlet and outlet of the circulating water pump,the PID temperature program for the inlet and outlet of the plate heat exchanger,and the PID differential pressure control program for the water pump.Finally,the sub program called in the PLC operation process is compiled.The success of PLC programming brings about the realization of data transmission,detection,control and other functions.Thus,the touch screen of the monitoring system can be used for system data management,historical records search,and change trend prediction of equipment operation parameters.The touch screen of the upper computer of the intelligent heat exchange unit realizes friendly man-machine dialogue.The touch screen can directly display the parameters and operation status of each equipment.After many times of operation test and monitoring,the intelligent heat exchange unit meets the change needs of the air conditioning fresh air unit.