Functional Features and Calibration Steps of pH Meter
PH meter calibration steps
Insert the composite electrode into the measuring electrode socket;
Turn the selection switch knob to the PH position;
Press the "Temperature" button to enter the solution temperature adjustment state of the instrument. Press the "▲" or "▼" buttons on the "Temperature" button to adjust the temperature display value to rise or fall, so that the instrument displays the current solution temperature value. Then press the "Confirm" button to confirm the solution temperature and return to the pH measurement state.
Insert the electrode, which has been cleaned with distilled water and dried with filter paper, into a standard solution with a pH of 6.86 using a pH meter. After the reading stabilizes, press the "positioning" button (at this time, the pH indicator light flashes slowly, indicating that the instrument is in the positioning calibration state). Adjust the pH display value up or down by pressing the "▲" or "▼" on the "positioning" button, so that the instrument display reading is consistent with the pH value of the buffer solution at that temperature. Then press the "confirm" button (for example, when mixed phosphate is 10 ℃, pH=6.92).
Turn the slope adjustment knob clockwise all the way to the 100% position; Adjust the positioning adjustment knob to make the instrument display reading consistent with the pH value of the buffer solution when the temperature drops (such as when using mixed phosphoric acid to position the temperature at 100 ° C), PH=6.92)
Insert the electrode cleaned with distilled water and dried with filter paper into a standard solution with pH=4.00 (or pH=9.18). After the reading stabilizes, press the "Slope" button and adjust the pH display value to rise or fall by pressing the "▲" or "▼" on the "Slope" button, so that the reading is the pH value of the solution at that time. Then press the "Confirm" button, and the instrument enters the pH measurement state. The pH indicator light stops flashing and the instrument completes calibration. Measurement can only be carried out after calibration is completed.
Structure of PH meter
1. A reference electrode;
2. A glass electrode whose potential depends on the pH of the surrounding solution;
3. A current meter that can measure small potential differences in circuits with high resistance.
The following are separate explanations of the main functions of each component:
1. The basic function of a reference electrode is to maintain a constant potential as a control for measuring various deviation potentials. Silver silver oxide electrode is currently a commonly used reference electrode in pH.
2. The function of a glass electrode is to establish a potential difference that reacts to changes in the hydrogen ion activity of the measured solution. By placing the pH sensitive electrode and the reference electrode in the same solution, a primary cell is formed, whose potential is the algebraic sum of the potentials of the glass electrode and the reference electrode. E-battery=E-reference+E-glass. If the temperature is constant, the potential of this battery changes with the pH of the solution to be measured. However, measuring the potential generated by the battery in a pH meter is difficult because its electromotive force is very small and the impedance of the circuit is very large, ranging from 1-100M Ω. Therefore, the signal must be amplified enough to drive a standard millivoltmeter or milliammeter.
3. The function of an ammeter is to amplify the potential of the primary battery several times, and the amplified signal is displayed through the ammeter. The degree of deflection of the ammeter pointer indicates the strength of the signal it pushes. For practical use, the pH ammeter dial is engraved with the corresponding pH value; The digital pH meter directly displays the pH value in numbers.
