I. Product Overview
CA80COD is an online COD analyzer based on the potassium dichromate method, suitable for continuous monitoring of chemical oxygen demand in surface water, domestic sewage, and industrial wastewater. The instrument complies with China's environmental protection industry standards and features automatic calibration, automatic cleaning, and remote communication functions, enabling long-term unattended operation.
This document is a quick operation guide for the CA80COD, covering installation, commissioning, maintenance, and common troubleshooting, for reference by engineering technicians and procurement personnel.
II. Measurement Principle and System Composition
2.1 Measurement Principle
The CA80COD adopts the potassium dichromate high-temperature digestion-colorimetric method. In a strongly acidic medium, potassium dichromate oxidizes reducing substances in the water sample, and the COD concentration is calculated by measuring the change in absorbance of Cr³⁺ at a specific wavelength. This method is consistent with the national standard GB 11914-89, providing accurate and reliable data.
2.2 System Composition
- Digestion unit: High-temperature heating module to ensure complete digestion of the water sample.
- Colorimetric unit: LED light source and photodetector to measure absorbance.
- Sampling and reagent system: Multi-channel peristaltic pump for precise control of sample and reagent volumes.
- Control and communication unit: Industrial-grade controller supporting 4-20mA, RS485, and Modbus protocols.
III. Main Technical Parameters
| Parameter | Specification |
|---|---|
| Measurement range | 0-5000 mg/L (selectable in segments) |
| Measurement accuracy | ±5% FS or ±10% of reading |
| Repeatability | ≤3% |
| Digestion temperature | 165℃ ± 2℃ |
| Measurement cycle | Minimum 45 minutes (adjustable) |
| Output signal | 4-20mA, RS485 Modbus |
| Power requirement | AC 220V ± 10%, 50Hz |
| Protection rating | IP54 (indoor) / IP65 (optional) |
IV. Installation and Commissioning Steps
4.1 Installation Environment Requirements
- Ambient temperature: 5-40℃, avoid direct sunlight.
- Relative humidity: ≤85%, no condensation.
- Installation location: close to the sampling point for easy reagent replacement and maintenance.
4.2 Commissioning Process
- Connect the sampling tube, reagent tubes, and waste liquid tube, ensuring no leaks.
- Connect power, turn on and preheat for 30 minutes.
- Enter the menu, set the measurement range, cycle, and output mode.
- Perform automatic calibration, using standard solutions to verify zero point and range.
- Start the automatic cleaning program to remove air bubbles from the tubing.
- Observe the first measurement result and compare with laboratory data; deviation should be less than 10%.
V. Daily Maintenance and Troubleshooting
5.1 Maintenance Points
- Check reagent levels weekly, replenish or replace in time.
- Clean the digestion cell and colorimetric cell monthly to prevent fouling from affecting absorbance.
- Replace peristaltic pump tubing quarterly to avoid sampling errors caused by aging.
- Calibrate the temperature sensor and photodetector annually.
5.2 Common Faults and Remedies
| Symptom | Possible Cause | Solution |
|---|---|---|
| High measurement value | Expired reagent or contaminated colorimetric cell | Replace reagent, clean colorimetric cell |
| Low measurement value | Blocked sampling tube or insufficient digestion temperature | Clear tubing, check heating module |
| No output signal | Loose communication cable or incorrect settings | Check wiring, verify communication parameters |
| "No sample" alarm | Sampling pump failure or low liquid level | Check sampling pump, confirm water sample supply |
VI. Precautions and Selection Recommendations
When using the CA80COD, always follow safe operating procedures and avoid contact with corrosive reagents such as potassium dichromate. It is recommended to confirm whether the measurement range, output signal, and protection rating meet on-site requirements before purchase. For water samples with high chloride ion content, models with chloride ion masking should be selected.
For the complete manual, please click the PDF icon above to download the CA80COD Chinese Manual.