A mineral processing plant has implemented automatic pH control, but the pH still fluctuates greatly, adjusts slowly, and even frequently requires manual intervention.

The following aspects can be focused on for inspection:

1. First, check the pH instrument
Whether the probe is contaminated, whether calibration is normal, and whether the installation location is reasonable.
If the measured value is inaccurate, automatic control has no foundation.

2. Next, check the reagent dosing system
Check:
Metering pumps, pipelines, valves, and the actual reagent dosage.
The fact that the PLC sends a normal control signal does not mean the reagent has actually been added as required.

3. Check the control parameters
If the PID parameters are set unreasonably, the following may occur:
Slow response, overshoot, and frequent adjustments.

4. Check process changes
Changes in feed rate, pulp density, ore properties, etc., will all affect the pH.
If the control strategy does not take changes in operating conditions into account, relying solely on PID may also have limited effectiveness.

5. Check the reagent addition point
The reagent addition location, mixing time, and the distance to the detection point will also affect the control effectiveness.
If the reagent has not been fully mixed after addition, the pH measurement value may not truly reflect the control effect.

Therefore:

Poor pH automatic control performance is not necessarily a PLC problem.

Troubleshooting should be carried out item by item in the following order:
Instrument → Reagent dosing → Process → Control parameters → Reagent addition point.

Only by truly connecting the three links of detection, execution, and control can pH automatic control be stabilized.