Popularize some knowledge about pH meters
A pH meter measures the acidity or alkalinity of a solution. Most organisms require proper pH levels to stay alive. The measurement of pH is crucial in many areas such as chemical processing, pulp and paper, food, beverages, pharmaceuticals and many more.
What is the main use of your pH meter?
A pH meter is an electronic instrument used to measure the pH value of liquids (there are also special probes to measure semi-solid substances) and can confirm the acidity or alkalinity of a substance. A typical pH meter consists of a special measuring probe (glass electrode) connected to a voltmeter that measures and displays the pH reading.
The probe measures pH - the activity of hydrogen ions in a thin-walled glass shell of ions around their tip. The pH meter measures and displays the small voltage produced by this probe (about 0.06 pH unit volts).
The pH meter circuit is similar to a voltmeter, but it does not indicate the voltage, but the pH value. Due to the high resistance (20~1000MΩ) of its glass electrode, the input signal must be very large. Therefore, a simple pH meter circuit usually contains an op amp in an inverting configuration with a total voltage gain of approximately -17 times. The inverting amplifier converts the small voltage generated by the probe (+0.059 V/pH) into a pH value. In order to display the pH value on the indicator, 7V is usually added to the result. For example, in a neutral pH solution, the output voltage of the probe is 0V. The displayed value of the pH meter is: 0×17+7 =7.
In alkaline solution, the output voltage range of the probe is 0 to 0.41V (7×0.059=0.41). Therefore, for a sample with pH=10 (pH value 3 units higher than neutral solution), 3×0.059=0.18V, the pH meter reading is 0.18×17+7=10. In acidic solutions, the probe's output voltage ranges from -0.41V to 0V. Therefore, for a sample with pH=4, -3×0.059=-0.18V, the pH meter reading is -0.18×17+ 7=4.
