Digital pH meter for industrial applications-sensor based

Digital pH meter for industrial applications

                             pH is a measurement of the acidity or alkalinity (base) of a solution.  When substances dissolve in water they produce charged molecules called ions.  Acidic water contains extra hydrogen ions (H+) and basic water contains extra hydroxyl (OH-) ions.

                            pH is measured on a scale of 0 to 14.  Neutral water has a pH of 7.  Acidic water has pH values less than 7, with 0 being the most acidic.  Likewise, basic water has values greater than 7, with 14 being the most basic.  A change of 1 unit on a pH scale represents a 10 fold change in the pH, so that water with pH of 6 is 10 times more acidic than water with a pH of 7, and water with a pH of 5 is 100 times more acidic than water with a pH of 7.

                           pH meter is essentially a voltmeter with high input impedance which measures the voltage of an electrode sensitive to the hydrogen ion concentration, relative to another electrode which exhibits a constant voltage. The key feature of the pH-sensitive electrode is a thin glass membrane that’s outside surface contacts the solution to be tested. The inside surface of the glass membrane is exposed to a constant concentration of hydrogen ions (0.1 M HCl). Allow the meter a few minutes to stabilize after you plug it in. When you are not using the meter, keep the electrode immersed in pH 7.0 buffers to a depth of about one inch. The meter must be calibrated by using standards of known pH before an unknown is measured. Since the unknowns are acidic, the pH 4.00 and pH 7.00 standards should be used. An accurate pH reading depends on standardization, the degree of static charge, and the temperature of the solution. 

                           In this project we measure the pH value of solutions using pH meter. pH meter is an electrode which gives the voltage according to that solutions. For example it gives negative voltages for acids, positive voltages for bases, water is zero voltage at room temperature. i.e.  0 to 7 for acids, 7 to 14 for bases and 7 for water.  In this project pH meter measure the values and give to adc and adc convert those values to digital voltages. and this voltages are displayed on lcd.


  1. Accuracy
  2. Ease of use
  3. Objectivity
  4. Precision
  5. Consideration.


Software Tools:

  1. Keil compiler
  2. Orcad.
  3. Proload.

Hardware Tools:

  1. AT89S52
  2. pH meter
  3. ADC 0808
  4. LCD
  5. BUZZER 

Block diagram: