MAINTENANCE OF AUTOMATION PART
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The automation part of the wastewater treatment system includes PLC, HMI/SCADA, inverter, measuring sensors, pump-fan-air blower control system, control cabinets and industrial communication protocols. Regular maintenance helps ensure stable operation, reduce the risk of system downtime, prolong equipment life and ensure the quality of the output wastewater.
1. Maintenance objectives
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Ensure PLC, HMI, SCADA operate stably, without system hang.
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Minimize sensor errors that cause measurement errors, leading to incorrect control.
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Ensure control response speed and PID loop stability.
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Prevent inverter overload, motor burnout, fieldbus communication errors.
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Avoid the risk of stopping the entire system due to electrical cabinet errors.
2. Main maintenance items
2.1 PLC (Programmable Logic Controller)
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Check RUN/STOP status, fault, error log.
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Backup PLC program and firmware.
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Check 24VDC power supply stability.
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Check I/O module: loose contact, rust, weak contact point.
2.2 HMI / SCADA
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Clean the screen, check for dead pixels.
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Check warning logs, load memory, event history.
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Optimize the interface, avoid screen freezes.
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Check the database storing operational data.
2.3 Inverter (VFD)
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Check load, temperature, OCR, OVL, OHT faults.
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Check the cleanliness of the radiator and cooling fan.
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Check the power cable, tighten the cos head.
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Backup the parameter.
2.4 Measuring sensors
Including:
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DO (Dissolved Oxygen)
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pH
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ORP
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Ultrasonic Water Level / Pressure
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Magnetic Flow
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TSS/SS Sludge
Implementation:
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Clean the probe, calibrate periodically.
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Check the shield signal wire, anti-interference.
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Replace the optical transmission fluid (for optical DO sensors).
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Check for deviation from the manual sample.
2.5 Control cabinet
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Clean dust with compressed air, limit humidity.
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Check terminal connection, loose cos.
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Check temperature in cabinet.
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Check relay, contactor worn contact points.
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Check surge protection.
2.6 Industrial communication systems
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Modbus RTU/TCP-IP
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Profibus
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Ethernet/IP
Implementation:
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Check latency, packet loss.
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Check shielded network cable, RJ45 connector.
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Check conflicting addresses, baudrate.
3. Periodic maintenance work
Daily
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Monitor SCADA for abnormal signals.
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Check sensor errors by sample comparison.
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Monitor log alerts.
Weekly
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Test solenoid valve, protection relay.
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Check 4-20mA analog signal to PLC.
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Clean submersible sensor.
Monthly
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Calibration of pH, DO, TSS sensors.
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Check flowmeter error.
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Check inverter error.
Quarterly
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Backup PLC/HMI program.
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Check firmware update.
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Check Modbus connection.
Every 6 months
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Check the DC bus capacitor internal resistance of the inverter.
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Test contactor, semiconductor relay.
Every 1 year
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Replace inverter fan (if runtime is high).
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Evaluate the entire PID control loop.
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Control EMI interference in the electrical cabinet.
4. Risks of failure to maintain
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Pump does not follow water level → tank overflow/dry.
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DO aeration deviation → microbial death.
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ORP deviation → lack of Nitrate/Nitrite reduction.
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Increased power consumption.
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PLC error causes the entire system to stop.
5. Early warning signs
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SCADA displays abnormal fluctuations.
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Sensor signals fluctuate unsteadily.
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Inverter heats up quickly or intermittently reports errors.
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Control response delay.
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Communication disconnection warning.
6. Advanced Recommendations
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Install a separate UPS for PLC/SCADA.
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Set up HMI operation authorization.
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Optimize PLC code to reduce scan time.
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Save historical logs, warnings, alarm trending.
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Install a temperature sensor in the electrical cabinet.
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Use standard shield + earthing.
7. Records to be kept
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Maintenance log.
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Sensor calibration log.
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PLC/HMI/SCADA backup file.
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Monthly fault report.
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Measurement signal trend chart.
8. Conclusion
Automation maintenance is the core factor to help the wastewater treatment system operate stably, reduce repair costs, maintain output water quality to meet QCVN and ensure safety for microorganisms.
CÔNG TY TNHH CAMIX
34 - 36, Đường 57A, P.Tân Tạo, Q.Bình Tân, Tp.HCM
Tel: (028) 3601 5966 - Fax: (028) 5407 3938 - Email: info@camix.com.vn
Hotline: 0903.318.778 (Ms.Phuong Linh) - 0976.164.441 (Mr.Anh Khoa)
