Why does the value displayed by the online pH meter transmitter fluctuate so much?
The displayed value of the online pH meter transmitter was unstable and fluctuated too much. When it was first used, it malfunctioned 2 hours after the standard solution was calibrated. The specific phenomenon is: the PH value of the measured medium is between 6.8 and 7.2. When the PH value is 6.8, the transmitter display value changes between 5.9. When the PH value is 7.2, the transmitter display value decreases at 11. Regret slowly decreases downward to 10. This phenomenon did not occur after replacing the new transmitter.
The problem of large fluctuations in the displayed value of the online pH meter transmitter is definitely rare. There are not many problems with imported pH meters, and this problem occasionally occurs. Want to see if the probe needs to be replaced? Replace the probe with a new one and check the impedance. Check the salt bridge without changing the probe. Finally, whether to consider replacing the probe. The wiring may be loose, tighten the terminals.
Note: Salt bridge. After the reference electrode is inserted into the solution under test, a small amount of KCl solution leaks out through the porous ceramic. It is connected internally to the reference electrode and externally connected to the solution under test, which acts as a bridge for electrical contact. It is called a salt bridge. . The leakage speed of E salt bridge solution has a great influence on the liquid junction potential: the leakage speed is too slow, causing the liquid junction potential to be unstable; and if the pressure of the measured solution increases, the leakage speed will be slower, and the measured solution may enter inside the reference electrode, causing the acidometer to malfunction.
At pH 6.8~7.2, the number of hydrogen ions changes around 4, which is very weak when converted into mv signal. If the amplifier amplifies according to this ratio and changes to a different buffer, it will probably indicate -2 or 16.
Combined with the fact that the fault disappeared after you changed the transmitter, I believe it was a coincidence. If you had not changed the buffer at all at that time, the pH would probably have jumped around. It was just a coincidence. 7.2 buffer? Generally, 4.0, 6.86 (or 7.0), 9.18 (or 9.0) are common, and for pH calibration, the buffer must differ by more than 2.0.
Assuming that the pH of the solution is basically unchanged, the common reasons why the displayed value of the online pH meter transmitter fluctuates greatly and the reading often jumps are:
1. Poor grounding, including the pipeline between the transmitter and the electrode
Sometimes if you shake the special cable with your hand or touch the metal shell of 253, the pH reading will change greatly;
&2. The electrode form is set incorrectly, which is very consistent with the phenomenon you mentioned 7
asymmetrical asymmetrical connection and symmetrical symmetrical connection;
3. The slope of the last calibration is too low.
