Team:NCKU Tainan/pH meter

pH Meter

About this section, we are showing how to use the pH meter in arduino.

Motivation


Because E. coli is sensitive to pH value, and according to the experiment of the pH sensor by WET members. We know that E. coli can’t grow below pH value of 6, and generally grow the best at pH 7.



Experiments


  • Experiment 1: Instrument calibration

    1. Purpose

      • Because the buffer solution wouldn’t change too much in the environment, we used the buffer solution to calibrate the pH meter to ensure that the deviation would be the same every time.

    2. Method

      1. Insert pH meter into buffer solution of pH 7, wait for 1 min, it will achieve a stable value.

      2. Minus the value with pH 7, and it will get the offset value. For instance, 7-7.09=-0.09.

      3. Write the offset value into code, and then upload the code into Arduino again.

      4. After rinsing the pH meter, we will insert it into pH 4 buffer solution.

      5. If it is found to be too different from the error of pH 4, you should adjust the knob. After inserting pH 4, it is found that the error with pH 4 is very large.

      6. Adjust the knob. (Remark: Because the change of the knob is small, it may have to turn a few more times until display pH 4.)

      7. Finally, it can be found that the measured pH is 4.


  • Formula calculation

    1. voltage = analog value*5/1024

    2. pH value = 3.5*voltage+offset

  • Experiment 2: Precision measurement

    1. Purpose

      • We assume that pH 4 to 7 is linear, so we want to verify whether it is linear between pH 4 to 7. By measuring the solution of pH 4.7, compare its deviation.

    2. Method

      • Mix a solution with pH=4.7 and measure with a calibrated pH meter.

    3. Result

      • After inserting the solution with pH=4.7, we found that the value was stable at pH 4.83 with an error of about 0.13, which roughly met the error of this pH meter ± 0.1 pH.


    4. Materials used

      1. Arduino UNO

      2. pH sensor
        1. Module Power : 5.00V
        2. Measuring Range:0-14pH
        3. Measuring Temperature :0-60 ℃
        4. Accuracy : ± 0.1pH (25 ℃)

      3. pH buffer solution

      4. Arduino code

Wiring


Reference


  1. Boywhy Chen.(2016).[Arduino] PH meter. Retrieved from
    http://boywhy.blogspot.com/2016/07/arduino-ph-meter.html(Augest 28,2018)




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