Analysis of pH meter malfunction examples
1. During the use of the acidity meter, it was found that the instrument cannot be zeroed when adjusting the zero potentiometer, but the number can be changed
Fault inspection and analysis: Under normal conditions, the instrument can jump by adjusting the zero potentiometer. Check the preamplifier and use a multimeter to measure the DC voltage range of the preamplifier integrated block. It was found that the voltage cannot be adjusted, indicating a circuit fault in this area. Further measurement revealed that it was due to mismatched insulated field-effect transistors. Change the resistance of the paired field-effect transistors to match.
Troubleshooting: After replacement, the instrument was put into normal use.
2. The pH meter indicates no change
Fault inspection and analysis: If there is no change in the instrument indication, it may be due to transmitter malfunction or probe contamination, which prevents normal measurement. A signal transmitter is used to simulate the probe and send a signal to the transmitter. The transmitter output changes, but the transmitter is normal. After disassembling and inspecting the pH analysis probe, contamination was found on the probe.
Troubleshooting: After cleaning the probe, the instrument panel returned to normal.
3. The pH meter shows severe fluctuations
Fault inspection and analysis: The causes of severe fluctuations in instrument readings include fluctuations in transmitter power supply, circuit faults, or problems with the connection between the transmitter and the measuring probe. A signal transmitter is used to simulate the probe sending a signal to the transmitter, and the transmitter output changes normally. There is no problem with the transmitter, and the power supply is also stable. The problem lies in the connection cable or line connection.
Fault handling: After replacing the connecting cable, the instrument display is normal.
4. The glass pH electrode and circuit of the industrial pH meter are intact, but after being put into operation, the measurement error is large, and even cannot work normally
Fault analysis: The analysis is caused by two reasons. Firstly, the insulation impedance of the shielded cable, junction box or terminal between the pH electrode and the high resistance converter is reduced. Due to the high internal resistance of glass pH electrodes, insulation degradation can occur if the terminals between the pH electrode and the converter become damp, the shielded cable becomes moldy, the potassium chloride solution used for the reference pH electrode contaminates the terminal box or seeps into the cable curtain, oil or sewage residue left on the terminals during maintenance, or if the terminal box is not sealed and dust accumulates in it. Secondly, there are large mechanical and electrical equipment near the installation environment of the instrument, and excessive current interferes with the instrument readings.
Troubleshooting: Take appropriate measures.
5. When measuring with a pH meter, the measurement is inaccurate
Fault inspection and analysis: Upon inspection, it was found that the tested medium contained oil contamination. This is because when the medium contains a large amount of oil impurities, it can contaminate the pH electrode.
