Research Of Ph Control Method Based On Low Liquor Ratio Cheese Dyeing Process

Low liquor ratio cheese dyeing machine is a new concept dyeing machine which is basedon the three-level impeller pump and its pulsating flow control method. Compared withtraditional cheese dyeing machine, it has the advantages of energy-saving and high efficiency,and it takes shorter time, less dyes and dyeing auxiliaries to complete one dyeing cycle.However, low liquor ratio dyeing has little dye. As a result, small dyeing auxiliaries addingerror will cause dramatic changes of pH value in the dye, which affects the dye’s uptake rateand fixation rate, leading to increase in the residual amount of the dye in the dyeing liquid,aswell as some kinds of dyeing defects.Moreover, artificial method of adjusting pH value intraditional cheese dyeing process demands the operator should have rich experience in dyeingprocess. This adjustment method has a very low efficiency, as well as, results in an increase inthe consumption of dyeing auxiliaries and water. Therefore, considering to enhance dyeingefficiency, improve the dyeing quality and reduce the consumption of dyeing auxiliary, it is ofgreat significance to study the control method of pH value in the low bath rate cheese dyeingprocess.The paper analyses the mechanical structures, the working principle of cheese dyeingmachine, as well as the characteristics of low liquor ratio dyeing technology. According tothose characteristics, the automatic control solution of pH value is put forward. The pHregularity in the three stages-pretreatment phase, dyeing phase and post-processing phase-isanalyzed in detail, which can provide the settings input for pH feedback regulation. The paperestablishes the mechanistic model of pH regulation in cheese dyeing process, from what wemake the following conclusion: the model has a big gain coefficient near the point pH=7, andaway from the neutral point it has a small gain coefficient.The model has a severe nonlinearcharacteristics. According to the characteristics of pH adjustment in the cheese dyeing process,intelligent interval adjustment method is designed to determine intelligently the amount ofacid or alkali to add by the output of a PID controller. In order to overcome the severenonlinear characteristics during the pH adjustment, the three-stage nonlinear process gaincompensation approach is adopted to determine the coefficient of the PID controller. In orderto improve the accuracy of the pH control,the approach ensures that the pH control system hasa unified open-loop gain coefficient, providing a theoretical method for pH control in the lowliquid ratio dyeing process.In addition, the paper elaborates the structures of hardware platform and theimplementation of software for the automatic control system of pH in low liquor ratio cheese dyeing process. The lower controller PLC communicates with the pH transmitter viaMODBUS protocol, achieving the purpose of onsite data gathering. The host computercommunications with the PLC via HMI protocol, achieving the purpose of centralizedmanagement of onsite data. In the software development process, database technology andmulti-threading technology are applied to ensure the fluency and real-time of data processingand human-machine interface display.Finally, applying the PH value monitoring system to a small bath for cheese dyeingprocess, from the data analysis, we conclude that the method of pH value control is suitablefor low liquor ratio cheese dyeing. This method can shorten the dyeing cycle, reduce theconsumption of dyeing auxiliaries, water, electricity and steam, as well as ensure the qualityof cheese dyeing.