The intelligent CDS liquid supply system achieves path-to-±1% concentration error control.

1. High-Precision Real-Time Concentration Monitoring and Feedback

1. Applications of Optical Concentration Sensors

Employing online concentration sensors based on the principle of light refraction (such as the NMF model), these devices measure the refractive index of the solution in real time to obtain accurate concentration data. With an accuracy of up to ±0.3%, these sensors support 4-20mA or RS485 signal output and can be directly integrated into control systems, providing real-time feedback for PID regulation.

• Technical Advantage: Built-in temperature calibration function reduces the impact of temperature fluctuations on concentration measurements, making it ideal for monitoring chemical solutions such as acid liquids and alcohol.

2. Dynamic Shear Force Sensor (Moving Blade Type)

For high-viscosity or particle-containing solutions (such as pulp), a moving-blade sensor is used to measure concentration via active shear force, offering a sensitivity of ±0.02%, a response time of less than 10 seconds, and being unaffected by changes in flow rate.

II. Optimization of the PID Control Algorithm

1. Parameter Tuning Strategy

• Guidance via mnemonic: Follow the rule "Adjust parameters step by step to find the optimal settings—start small, check sequentially from low to high; first fine-tune the proportional (P) parameter, then the integral (I), and finally add the derivative (D) at the very end."
• Dynamic adjustment: The proportional term (P) quickly responds to concentration deviations, the integral term (I) eliminates steady-state error, and the derivative term (D) suppresses overshoot. For instance, when the system oscillates, increase the P value; if the static error is large, increase the I value by 23.

2. Implementation of Closed-Loop Control

Through the PLC programmable logic controller, sensor data is compared with set values to dynamically adjust the metering pump speed or valve opening, ensuring that the concentration remains stable within a range of ±1%⁴.

III. Hardware Optimization of the Liquid Supply System

1. Precision Measurement and Flow Control

• Metering pumps: Utilizing high-precision metering pumps (such as diaphragm pumps), combined with variable-frequency speed control technology, these pumps allow for stepless flow adjustment, perfectly meeting diverse process requirements⁵.
• Flow meter: A mass flow meter or electromagnetic flow meter continuously monitors the flow rate, and the feedback signal is used to dynamically adjust the pump speed, ensuring a mixing ratio accuracy of 5%.

2. Filtration and Defoaming Treatment

• PFA Filter: Features a separate housing and filter element design, offering exceptional resistance to strong acid corrosion, high filtration accuracy, and minimizing impurities' impact on concentration.
• Deaerator: Eliminates bubbles generated by the metering pump's vibration, preventing bubble interference with concentration measurements and solution stability—key factors in ensuring accurate and reliable results.

3. Double-tube Safety Design

An inner-and-outer dual-pipe structure ensures that if the inner pipe leaks, the chemical liquid flows into the gap between the two pipes and is immediately captured by the leak detector, preventing contamination or abnormal concentration levels.

IV. Environmental and Safety Controls

1. Pressure and temperature are stable

• Pressure sensor: Monitors pipeline pressure and adjusts it via backpressure valves and pressure-reducing valves, preventing pressure fluctuations from affecting flow rate and concentration⁵.
• Temperature sensor: Combined with heating/cooling devices (such as electric heaters and chillers), it maintains a constant solution temperature, preventing concentration drift caused by temperature fluctuations⁵.

2. Leakage and Explosion-Proof Measures

• Leak detectors are installed at critical points (such as liquid supply tanks and valves), and the linked alarm system promptly addresses any leaks.
• Explosion-proof design is suitable for flammable solvents, including explosion-proof lighting and gas detectors 6.

5. System Maintenance and Calibration

1. Regularly calibrate the sensor

The concentration sensor must be regularly calibrated to zero using a standard solution (such as distilled water) to ensure measurement accuracy. For example, the NMF sensor is recommended to be verified every six months, and after 5 years of operation, an insulation resistance test is required.

2. Automated Maintenance Management

The PLC system features fault diagnosis and solution dosage statistics functions, enabling remote monitoring when combined with a touch screen or host computer software, thereby reducing errors caused by manual intervention.

Summary

The key to achieving ±1% concentration error control lies in the integrated approach of "real-time monitoring + dynamic adjustment + hardware assurance."

• Sensor layer: High-precision optical or shear-force sensors provide real-time data;
• Control Layer: The PID algorithm, combined with a PLC, achieves closed-loop control.
• Executive Level: Precision metering pumps, filter-foam removal devices, and a double-tube design ensure hardware stability.

By leveraging the synergy of multiple technologies, the CDS system can meet the stringent requirements of high-precision processes in industries such as semiconductors and chemicals.

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