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hat Is a COD Digital Sensor?

A COD digital sensor is a self-contained submersible probe that measures Chemical Oxygen Demand (COD) directly in water — without chemical reagents — and outputs the result as a clean digital signal via RS-485 or Modbus RTU protocol.

The word digital distinguishes these sensors from older analog COD transmitters that output a raw 4–20 mA current signal requiring external signal conversion and susceptible to noise over long cable runs. A digital COD sensor processes the measurement internally and transmits precise, noise-immune data directly to any PLC, SCADA, data logger, or cloud platform over standard Modbus protocol.

The measurement principle is UV absorption spectroscopy: organic compounds in water absorb ultraviolet light at characteristic wavelengths. By measuring UV absorbance, the sensor calculates COD equivalent values continuously, in real time, with no waiting for laboratory digestion.

Introducing the Kainafu KNF-1008APro

The KNF-1008APro is Kainafu's smart COD digital sensor — an advanced evolution of the UV absorption COD method using dual wavelength measurement at 254 nm and 546 nm simultaneously. The dual-wavelength approach provides superior accuracy over single-wavelength designs by enabling automatic compensation for color and turbidity interference — the two most significant error sources in UV-based COD measurement.

Beyond COD, the KNF-1008APro simultaneously derives BOD, TOC, and turbidity from the same dual-wavelength optical measurement — delivering four parameters from one probe installation.

Full Technical Specifications

Why Dual Wavelength Makes a Difference

Single-wavelength UV COD sensors measure absorbance only at 254 nm. This works well in clean water but introduces significant errors in real-world wastewater where:

• Turbidity — suspended particles scatter UV light, causing falsely elevated readings
• Color — naturally colored water (humic acids, industrial dyes) absorbs UV independently of organic COD content

The KNF-1008APro measures at both 254 nm and 546 nm simultaneously. The 546 nm measurement captures the contribution of turbidity and color to the overall optical signal. By subtracting this contribution from the 254 nm reading, the sensor delivers a corrected COD value that accurately reflects true organic load — even in heavily turbid or colored wastewater.

The result: significantly better accuracy in the complex, variable water matrices found in real monitoring applications.

Key Features

✅ Four Parameters, One Probe

COD, BOD, TOC, and turbidity simultaneously — one installation point, one cable, one Modbus address. No need to deploy separate sensors for each parameter.

✅ <10 Second Response Time

Detects organic load changes within 10 seconds — enabling real-time process control and immediate alarm response to pollution events, rather than waiting for laboratory results hours later.

✅ Integrated Self-Cleaning Brush

A built-in mechanical cleaning brush prevents biofouling on the optical windows — essential for long-term unattended deployment in wastewater environments where biological growth would otherwise rapidly degrade UV measurement accuracy.

✅ No Reagents — Zero Chemical Cost

No potassium dichromate, no sulfuric acid, no mercury, no hazardous waste. The KNF-1008APro eliminates all chemical procurement, storage, handling, and disposal costs associated with traditional COD analysis.

✅ Standard Modbus RTU — Universal Integration

RS-485 Modbus RTU output integrates directly with any PLC, SCADA, DCS, or third-party data acquisition system — as well as the Kainafu KNF-300 and KNF-400 series monitoring systems and cloud platform.

Application Scenarios

Wastewater treatment plant influent and effluent — real-time organic load monitoring for process optimization and discharge compliance

Industrial effluent discharge points — continuous COD surveillance at factory outfalls for regulatory reporting and pollution incident detection

River and surface water monitoring — early warning of upstream industrial discharge at river cross-sections and catchment monitoring points

Small water quality stations and buoy systems — compact size (D32 × L175 mm) and low power (0.4W) make the KNF-1008APro ideal for solar-powered remote deployments

Municipal sewage network nodes — combined with the KNF-400D system for manhole-deployed COD monitoring

System Integration

Data from all deployments uploads to the Kainafu cloud platform (ion.onetestinc.com) — real-time dashboards, configurable COD threshold alarms via WeChat and APP, historical trend analysis, and compliance data export.

KNF-108A vs KNF-1008APro — Which to Choose?

Choose the KNF-1008APro when monitoring water with variable turbidity, natural color, or when BOD values are also required. Choose the KNF-108A for high-concentration industrial effluent where the extended COD range (up to 1,500 mg/L custom) is needed.