In water treatment equipment (such as purified water systems and wastewater treatment devices), a pH meter is an essential instrument for monitoring the acidity and alkalinity of water quality. Its data directly guides key processes such as chemical dosing adjustments and membrane system protection. The complete usage process of a pH meter can be detailed in four stages: Preparation, Installation and Calibration, On-Site Use, and Daily Maintenance.

 

#### I. Preparation: Confirm Instrument Status and Supporting Materials

 

**Instrument Inspection**

 

- Verify that the pH meter main unit (such as an online transmitter) and the electrode (commonly a glass electrode and reference electrode combination) are intact. Check that the glass bulb of the electrode is free from cracks, the reference liquid (such as KCl solution) is not leaking or dried out, and that the cable connectors are corrosion-free.

  

- Prepare necessary tools: calibration buffer solutions (common pH values of 4.00, 7.00, 10.00; choose based on water quality scenarios, e.g., use 4.00 and 7.00 for acidic water treatment, 7.00 and 10.00 for alkaline), electrode cleaning solution (distilled water or deionized water; use diluted hydrochloric acid/alcohol if heavily contaminated), and soft cloth/filter paper.

 

**Installation Environment Confirmation**

 

- The online pH meter should be installed in a location with stable water flow and no violent vibrations (such as after pretreatment or before RO membrane feed), avoiding proximity to strong electromagnetic devices (like pumps) to prevent signal interference.

  

- Ensure that the electrode is fully submerged in water and situated away from dead spots in the pipeline (to avoid stagnant water contact). If necessary, install a flow cell (to ensure a water flow speed of 0.1-0.5 m/s; too slow may lead to scaling, too fast may damage the electrode).

 

1. **Electrode Calibration (Key Prerequisite to Avoid Data Deviation)**

 

   - **Clean the Electrode**: Rinse the electrode surface with distilled water and use filter paper to absorb moisture (do not wipe the glass bulb to prevent scratches).

   

   - **Two-Point Calibration (Common Mode)**:

     - First, place the electrode in the pH=7.00 standard buffer solution, press the "calibrate" button on the main unit, and wait for the value to stabilize (usually 30-60 seconds). Confirm that the main unit displays "Calibration 7.00 successful."

     - Rinse the electrode with distilled water and dry it, then place it into the second standard solution (either pH=4.00 or 10.00), repeating the calibration process until the main unit displays "Calibration complete."

   

   - **Post Calibration Verification**: Place the electrode back in distilled water; the value should stabilize between 6.5-7.5. If the deviation exceeds 0.2 pH, recalibration is necessary (if multiple recalibrations fail, check if the electrode is aging).

 

2. **Device Installation and Power On**

 

   - Secure the electrode in the pre-set position according to the manual (for pipeline interfaces, use threaded seals to prevent leaks), and connect the electrode cable to the main unit, ensuring the connections are secure (distinguish between signal and power lines to avoid reverse connections).

   

   - Turn on the main unit, set monitoring parameters (such as data refresh rate of 1-5 seconds, alarm thresholds; for example, in a purified water system, set the pH alarm range typically between 4.0-7.5), and enter "Real-Time Monitoring" mode, observing whether the values stabilize (initial fluctuations are normal; they should stabilize within 5-10 minutes).

 

3. **On-Site Use and Data Recording**

 

   - During normal operation, continuously observe the displayed pH meter values. If the value exceeds the process range (for instance, the pH of RO membrane feed should be controlled between 5.5-7.0 to prevent membrane oxidation or scaling), promptly coordinate with the dosing system (such as adding acid/base for adjustment).

   

   - According to GMP or equipment management requirements, regularly record data (e.g., every hour). Record details including time, pH value, alarm triggers, and adjustment measures (like dosing amounts) to ensure data traceability.

 

#### III. Daily Maintenance: Extend Lifespan + Ensure Accuracy

 

**Short-Term Maintenance (Daily/Weekly)**

 

- Daily check the electrode surface for dirt or scaling (e.g., calcium carbonate precipitate). If present, gently wipe it with a soft cloth dipped in diluted hydrochloric acid (5% concentration), then rinse thoroughly with distilled water.

  

- Weekly perform a "spot check calibration" with standard buffer solutions to ensure the deviation is ≤0.1 pH; if exceeded, recalibrate.

 

**Long-Term Maintenance (Monthly/Quarterly)**

 

- Monthly check the KCl solution level in the reference electrode; if it is below the marked line, promptly replenish with saturated KCl solution (do not substitute with distilled water, as it may affect the reference potential).

  

- Quarterly, remove the electrode and soak it in electrode activation solution (e.g., 0.1 mol/L hydrochloric acid) for 30 minutes (this addresses aging of the glass bulb that leads to slower response), restoring the electrode's sensitivity.

  

- If the electrode has been in use for over 1-2 years, consider replacing it.