The pH value is monitored in many industries,such as protection,chemicals,food,medicine, environmental and so on.So a pH value monitor was designed based on MCU control.AT89S52 SCM is the main control in the design of hardware;the pH complex electrode is adopted as the sensor;in order to match the high internal resistance of the sensor, third class amplifier circuit is composed of CA3140,UA741 in the signal conditioning.A/D converter is implemented through ADC0809.The data traffic is accomplished through the SCM and RS232 serial communication interface;the LCD1602 screen is used to display the pH value in real time. The C language is adopted to prepare control procedure in the software design,and the Visual C++ software is used to prepare the computer monitoring interface,so that the teledata monitoring can be finished easily. The corresponding debugging methods are given. to against the problem in the design of actual circuit. According to the measurement principle of pH value composite electrode and electrode structure, the pH value of temperature compensation is carried on.In order to increase the measuring accuracy the pH sensor.has been carried on to the calibration and correction After experimental testing, equipment testing can reach 0.1 percent.This design has many featuers,such as fewer components,small size,easy maintenance and low cost.
Key words：pH Composite Electrode AT89S52 CA3140 Serial Communication
