Design And Experiment On The Dialysate PH Value And Electrical Conductivity Measuring Instrument

The kidneys are major organs of human body that remove metabolites, some waste and metabolic poisons through excretory function and retain moisture and other useful substances via reabsorption function to regulate water and electrolyte, maintain the balance of acid-base. Kidney disease is a common and frequently-occurring disease, and it’s large number of patients. Because of the insufficient supply of renal blood flow and renal damage suffered some functional and poisons damage those likely cause acute renal failure. Due to long-term nephropathy and the deterioration of the disease with time, kidney function gradually decreased and cause chronic renal failure, eventually lead to uremia. In recent years hemodialysis as the effective treatment for acute and chronic renal failure has been widely used in clinical practice. Hemodialysis treatment can release disease condition, maintain the normal physiological function of human cells, remove waste products, reduce the occurrence of cerebrovascular event, decrease the disabled rate and mortality through prevention of concurrent multiple organ failure and promote the patients to return the society.In the process of hemodialysis the blood exchange with dialysate solute across the dialysis membrane to remove metabolic poisons, correct waste products and adjust the balance of acid-base. Thus, dialysate directly affect the clinical condition and prognosis of hemodialysis patients in a very critical role. Accompanied by the occurrence of complications during hemodialysis should not be ignored, such as low blood pressure, high blood pressure, disequilibrium syndrome and so on. Through the dialysate effect on the electrolyte, pH, and blood pressure control of patients adjustment is important for realizing individual dialysis on the basis of the clinical symptoms to reduce the incidence of complications, alleviate pain in the course of treatment and improve living quality of patients. Simultaneously through monitoring and control pH value of dialysate hemodialysis correct the electrolyte balance. When pH value is not proper, it can cause precipitation, acidosis and alkalosis. Those cannot achieve the purpose of treatment to delay the disease, and even endanger the patient’s life. So pH value should be monitored to reduce the negative impact on hemodialysis machine and dialysis treatment.With the development of the individual dialysis the individual treatment is made according to the needs of illnesses, so the measurement requirements of dialysate concentration are highly demanded more and more. The electrode conductivity measurement is mainly applied in the hemodialysis machine. But the electrode polarization and capacitance effect lead to low precision and large error, at the same time the measuring circuit is too complex and influence the real time performance. Yet due to the high resistance of pH electrode and external interference the measuring accuracy is severely affected. Therefore, this paper has developed a dialysate pH value and electrical conductivity measuring instrument. The variable frequency of bipolar interim pulse method is put forward to tremendously reduce polarization and capacitance effect on the conductivity measurement, temperature compensation formula of electrical conductivity has been improved. Meanwhile two-point correction method is used for calibration test and temperature compensation use the Nernst slope way to improve the accuracy of pH measurement which can achieve fast and accurate measurement of dialysate concentration and meet the testing requirement of dialysate concentration. This paper has designed hardware and software of dialysate pH value and electrical conductivity measuring instrument. Experiments and data analysis are carried.This paper introduces three aspects. The first aspect introduces the measuring principle of pH value and electrical conductivity and the hardware design of measuring instrument. First, this paper has analysised the measuring principle and the question which is needed to solve. On that basis relevant solution methods are proposed. Then according to function the instrument is divided into four modules which include the main control system, conductivity measuring module, the pH value measuring module and temperature measuring module to design circuits.The second aspect is the software design of measuring instrument. The software design includes architecture design, system software design, digital filtering process design and the temperature of electrical conductivity which was realized by programming. The software design is based on the hardware design on. First analysis the function of every module, and then design software flowchart, finally write the programs.The third aspect is to conduct calibration and validation experiments, and data has been analyzed by SPSS Statistics17.0software. PH value and conductivity calibration tests are made to determine the static performance parameters of the measuring instrument. The experiments are carried in the actual dialysate on the measuring prototype. Through the verification tests of pH value and T-test analysis it indicates that there is no significant difference between the measured value and standard value of pH value, and it is high degree of consistency. So the result indicates that measuring instrument can accurately measure the pH value of dialysate, and the two-point calibration method and the Nernst slope temperature compensation can improve the accuracy of pH measuring. At the same time, the result of electrical conductivity contrast experiment displays that the relative error between the measured value and standard value is less than0.5%. The error of variable frequency of bipolar interim pulse method is smaller than bipolar pulse method which can timely track the changes of dialysate concentration. The results show that the measuring instrument can achieve the accurate measurement of the dialysate concentration and meet the real-time testing requirement of dialysate in the hemodialysis machine. This measuring instrument can be widely used in the detection of dialysate concentration and achieve the individual dialysis treatment.