YEX-COD-308 Online COD Sensor: Reagent-Free UV Absorption Solution for Real-Time Water Quality Monitoring

Yexsensor YEX-COD-308 is a high-performance online COD sensor designed for continuous, accurate measurement of Chemical Oxygen Demand (COD), turbidity, and temperature in water bodies. Utilizing advanced dual-wavelength ultraviolet absorption technology at 254nm with turbidity compensation, this digital sensor delivers reliable data without reagents, reducing operational costs and environmental impact while supporting seamless integration into industrial automation systems via RS-485 Modbus/RTU protocol. Ideal for wastewater treatment, industrial effluent monitoring, and surface water quality management, the YEX-COD-308 ensures compliance with environmental regulations through fast response, low maintenance, and robust IP68 protection.

Discover the YEX-COD-308: Precision Online COD Monitoring for Modern Water Management

In today's stringent regulatory environment, real-time monitoring of organic pollutants in water is essential for industries and municipalities striving to maintain water quality standards and minimize environmental risks. The YEX-COD-308 Online COD Sensor from Yexsensor addresses these challenges head-on by providing a reagent-free, low-maintenance solution that measures COD, turbidity, and temperature simultaneously.

Engineered with dual light sources—one for UV absorption at 254nm to quantify dissolved organic pollutants and a reference light to compensate for turbidity interference—this sensor delivers stable, accurate readings even in complex water matrices. Its compact design, automatic cleaning brush, and digital output make it an ideal choice for continuous immersion installation in harsh conditions, from wastewater treatment plants to river monitoring stations.

By eliminating the need for chemical reagents associated with traditional laboratory COD methods (such as potassium dichromate oxidation), the YEX-COD-308 not only cuts costs but also prevents secondary pollution, aligning with green environmental protection goals. Users benefit from fast response times, minimal drift, and long-term stability, enabling proactive process control and rapid response to pollution events.

Whether you need to optimize treatment processes, ensure discharge compliance, or protect aquatic ecosystems, this sensor offers a complete, solution-oriented approach to water quality management.

Ⅰ、Working principle

Many organic compounds dissolved in water are absorbent to ultraviolet light. Therefore, the amount of dissolved organic pollutants in the water can be accurately measured by measuring the extent to which these organics absorb UV light at 254nm. The COD-308 online COD sensor adopts two light sources, one is ultraviolet light for measuring COD content in water and the other is reference light for measuring turbidity in water. In addition, the optical path attenuation is compensated by a specific algorithm and the interference of particulate suspended matter can be eliminated to a certain extent, so as to achieve more stable and reliable measurement.

Product features：

• No reagents, no pollution, more economical and environmental protection

• Small size, easy installation, and continuous water quality monitoring

• Measure COD, turbidity and temperature parameters

• Automatic compensation for turbidity interference

• With a cleaning brush to prevent bio-adhesion

• Small drift, fast response, more accurate measurement

• Excellent stability even for long-term monitoring

• Maintenance-free, long service life and low cost of use

• Digital sensor, RS-485 interface, Modbus/RTU protocol

• Low power design, anti-interference design

Ⅱ、Technical performance and specifications

1. Technical parameters

Ⅲ、Installation and electrical connection

1. Installation

Note: It is recommended to install a cable protective cover on the outside of the sensor cable. The sensor can be placed in any direction in the water. It is recommended that the sensor be placed horizontally and firmly fixed, and the measuring area should face the direction of the water flow.

2. Electrical connection

The cable is a 4-core twisted-pair shielded wire, and the line sequence is defined:

• Red line—power cable（12-24VDC）

• Black line—Ground wire（GND）

• Blue line—485A

• White line—485B

After the wiring is completed, it should be carefully checked to avoid the wrong connection before the power is turned on.

Cable specification: considering that the cable is immersed in water (including sea water) or exposed to air for a long time, the cable has a certain corrosion resistance. All interfaces of cable outer diameter Φ6mm, have been waterproof.

Ⅳ、Maintenance and maintenance

1. Maintenance schedule and method

1.1 Maintenance schedule

Note: The maintenance frequency in the above table is only a recommendation. Please maintain the sensor according to the actual usage of the sensor.

1.2 Maintenance method

1. Sensor outer surface: Clean the outer surface of the sensor with tap water. If there is still debris left, wipe it with a soft, damp cloth. For some stubborn dirt, add some household washing liquid to the tap water to clean it.

2. Check the cable of the sensor: the cable should not be tightened during normal operation. Otherwise, the cable inside the cable may be broken, causing the sensor to malfunction.

3. Check if the sensor's measurement window is dirty and the cleaning brush is normal.

4. Check the sensor's cleaning brush for damage.

5. For 18 months of continuous use, it is necessary to return to the factory to replace the dynamic sealing device.

1.3 Precautions

The probe contains sensitive optical and electronic components. Make sure the probe is not subject to severe mechanical shock. There are no parts inside the probe that require user maintenance.

2. Sensor calibration

2.1 Turbidity calibration:

1. Zero calibration: Take a small amount of turbidity liquid from a large beaker and place the sensor vertically in the solution. After 3 to 5 minutes, the value is stabilized and then zero calibration. The instructions refer to the appendix.

2. Slope calibration: Place the sensor in a solution and place it in a 100 NTU standard solution. After 3 to 5 minutes, the slope is calibrated after the value is stabilized. The instructions refer to the appendix.

2.2 COD calibration：

1. KHP(Potassium hydrogen phthalate ， C8H5KO4) , As a commonly used stain for environmental research, it can be used for COD calibration.

2. Preparation of standard solution

1. Accurately weigh 0.8503 g of KHP into a 1000 mL flask. Distilled or deionized water and perfused until the highest scale. This solution is a 1000 mg / L COD solution.

2. Take 100 mL of this solution into a 1000 mL flask and fill it to the highest mark with distilled or deionized water. After shaking, the COD concentration was 100 mg/L. A solution having a concentration of 20 mg/L was prepared in the same manner.

3. The concentrated standard solution (step 2.1) was stored in a black glass vial and stored at low temperature to prevent decomposition. The diluted standard (step 2.2) needs to be used within 24 hours of preparation.

2.3 Calibration (2-point calibration)

1. 0～200mg/L calibration

1. Place the sensor in a 5mg/L COD solution and verify that all light paths are submerged under water >2cm with no air bubbles. Perform a zero calibration according to the appendix command.

2. Place the sensor in a 200mg/L COD solution and slope calibrate according to the appendix command.

2. 0～500mg/L calibration

1. Place the sensor in a 20mg/L COD solution and verify that all light paths are submerged under water ≥2cm with no air bubbles. Perform a zero calibration according to the appendix command.

2. Place the sensor in a 400mg/L COD solution and slope calibrate according to the appendix command.

Warning:

• KHP have cancer risk and should be worn with gloves.

• When calibrating, firstly calibrate the temperature, then calibrate the turbidity and then calibrate the COD.

• If the slope is calibrated, the sensor value does not change within 3 minutes,re-supply after power is cut off.

3. Precautions

• Avoid the sun exposure of the sensor

• Please do not touch the sensor by hand

• Avoid contact with the sensor surface during measurement and calibration

• Avoid using any mechanical stress (pressure, scratches, etc.) directly on the sensor during use.

4. Common problems and countermeasures

Ⅴ、Quality and service

1. Quality assurance

• The quality inspection department has standardized inspection procedures, advanced and perfect testing equipment and means, and strictly in accordance with the regulations, 72 hours of aging experiments and stability tests on the products, and does not allow a substandard product to leave the factory.

• The receiving party directly returns the batch of products with a non-conformity rate of 2%, and all the costs incurred are borne by the supplier. The reference standard refers to the product description provided by the supplier.

• Guarantee the quantity of goods and the speed of shipment.

2. Accessories and spare parts

This product includes:

• 1 Sensor

• 1 Instruction manual

• 1 Certificate

3. After-sales service commitment

The company provides local after-sales service within one year from the date of sale, but does not include damage caused by improper use. If repair or adjustment is required, please return it, but the shipping cost must be conceited. Damaged on the way, the company will repair the damage of the instrument for free.

Frequently Asked Questions

Q1. What is the main advantage of the YEX-COD-308 over traditional laboratory COD methods?

The sensor provides real-time, continuous measurements without reagents, eliminating hazardous chemicals, reducing costs, and enabling immediate process adjustments—unlike lab methods that require hours for results and generate waste.

Q2. How does the dual-wavelength design improve measurement accuracy?

The 254nm UV light measures organic absorption for COD, while the reference light and algorithm compensate for turbidity and optical variations, resulting in more stable readings with reduced interference from suspended particles.

Q3. Is the YEX-COD-308 suitable for seawater or highly corrosive environments?

Yes, the 316L stainless steel housing and corrosion-resistant cable make it robust for various water types, including saline applications, provided operating conditions (temperature and pressure) are within specs.

Q4. What calibration frequency is typically required?

Calibration depends on regulatory needs and site conditions, but the sensor's low drift often allows intervals aligned with authority schedules. Two-point calibration using KHP standards is straightforward and ensures high accuracy.

Q5. Can the sensor be integrated with existing SCADA or PLC systems?

Absolutely. The RS-485 Modbus/RTU output supports direct connection to most industrial automation platforms for data logging, control, and remote monitoring.

Q6. How does the self-cleaning brush work, and when should it be serviced?

The integrated brush automatically prevents bio-adhesion on the optical window. Factory inspection and dynamic seal replacement are recommended every 18 months for continuous use to maintain optimal performance.

Q7. What power requirements does the sensor have for remote installations?

It operates on low power (0.3W at 12V), making it compatible with solar or battery-powered systems in remote monitoring stations.

Q8. Does the sensor measure only COD, or additional parameters?

It simultaneously measures COD, turbidity, and temperature, providing a more complete water quality profile from a single compact device.