PH Measurement Technology With Microprocessor

pH value is the basic parameter for the measure of acidity or alkalinity of a standard solution, and it is used widely in many fields such as electric power, environment-protection, chemical industry and so on. Potential measurement method based on the sensor with glass electrode is the most widely used way of measuring PH value, and the veracity is mainly affected by three factors : solution temperature, high resistance of glass electrode and electrode deviation.The paper is designed to devise and make a kind of intelligent meter for the measure of acidity or alkalinity using potential measurement method by sensor with glass electrode. Selecting PT100 platinum thermo resistance temperature sensor measures solution, compensate the glass electrode for temperature, uses bridge and single amplificatory circuit to magnify the sensor' s signal, uses software to revise the sensor, and measures the zero and saturation, eliminates the error of circuit system, advances the precision of compensate temperature. Adopting the high resistance and low excursion carrying the TLC2254 form the high resistance amplificatory circuit for measuring acidity electrode signal. In order to remove the input resistance which are caused by the creep age on electrode down-lead and the terminal, to adopt high impedance insulating line connect the electrode and weld the line on the printed circuitry board directly; at the same time, adding an insulating ring on the board so as to remove the effect on input resistance that caused by insulating resistance. Thesoftware revises the electrode error and displays the better result.The intelligent measure instrument of acidity and alkalinity take SCM as its core, adopt serial port parts, designed with CMOS integrate circuit, simple circuit, legerity structure, low wastage; has electrical source monitor circuit and doggy circuit, adopt the technique of photoelectric insulation to insulate the power supply source and measurement circuit to enhance the ability of anti-jamming and dependability. Adding protective circuit for input and output so that the instrument can' t be destroyed under high-voltage. This has a insulate RS485 standard serial port, compatible the series of ADAM4000, can be connected to RS485 main network and supported by combined software. The software process was compiled in Franklin C51 language and adopted module structure and some notes. The software realizes various functions, enact some parameter and can check it.In the lab, using exactitude signal FLUKE5500A and exactitude resistance box to simulate the glass electrode and platinum therrao resistance temperature sensor respectively, completed the test for the instrument. The result has shown a fact that the compensate temperature error is less than +0.2°C. The measure error for acidity is less than 0. 02PH.