Chromium is one of the essential trace elements for living organisms. The toxicity of chromium is related to its valence state. It is generally believed that hexavalent chromium is 100 times more toxic than trivalent chromium. Hexavalent chromium is more easily absorbed by the human body and accumulates in the body, leading to liver cancer. Therefore, China has designated hexavalent chromium as one of the indicators for implementing total quantity control.
Principle: Under high temperature conditions, oxidants oxidize chromium containing compounds in water samples to hexavalent chromium. Hexavalent chromium reacts with color reagents in acidic media to form a purple red complex. The absorbance of this complex is proportional to the chromium content in the water sample, thus obtaining the total chromium content in the water sample.
Suitable for laboratory analysis or detection of water used in industrial production processes, wastewater, urban domestic sewage, and surface water such as rivers, lakes, and seas.

（1）Micro level modular design concept
The microinjection system has a repeatability of less than 0.1% for 0.5mL and less than 0.4% for 0.05mL, with high resolution and a minimum quantitative volume of 0.5 μ L, ensuring the stability and accuracy of microinjection;
The total digestion volume is 2.5mL, and the single reagent dosage is 1mL, which is 1/5-1/20500ml of the reagent dosage of COD online monitoring instruments currently on the market. The reagent can be used for 40 days, greatly reducing secondary pollution;
The core single parameter module has a volume of 43.5 * 30.0 * 14.5cm (length * width * height), which is approximately equal to the size of a computer host. It can run independently and build multi in one instruments and larger workstation systems;
The preprocessing system, control system, signal acquisition system, display and operating system all adopt modular design, and the hardware adopts MODBUS bus and CAN bus design, which is easy to expand, optimize and upgrade;
The power components, pre-processing components, injection pump components, eight valve components, digestion tank components, hardware circuit components, and reagent kit components are all modular and easy to replace and maintain;



（2）Stable and reliable hardware structure with minimal maintenance
All made of 304 stainless steel, sturdy, durable and corrosion-resistant;
The front door is made of black tea PC material, which is resistant to impact, high temperature, corrosion, aging, and has a beautiful appearance that avoids light;
The injector adopts the American FLEX brand, and the operating carrier is clean water, which does not pass reagents or empty, avoiding wear and corrosion of the injection flow path, and has a longer service life;
The eight connected valve is independently developed (with applied invention patents) to ensure less cross contamination, stable performance, and greater durability;
The digestion high-pressure valve adopts the American ASCO 15kg solenoid valve, and is designed at a micro level to enhance its service life;
The liquid level detection is determined by a PTFE material float, which is corrosion-resistant, accurate in detection, and highly efficient;
The wiring harness process is made using original Japanese JST (gold-plated) or American AMP (gold-plated) brands, as well as matching original tools. The core components are made using American SEAT torque screwdrivers to ensure instrument quality;
Automotive grade Freescale processor chip, WINCE configuration system combined with FREERTOS embedded system dual system redundancy technology, ensures stable system operation;

（3）Accurate measurement, high reliability, and low detection limit
High precision injection pump system, high stability and low cross contamination eight valve components, ensuring accurate and stable liquid inlet volume;
The PID temperature control system, PID light source automatic adjustment, temperature and signal differential compensation design ensure the stability of the measurement system;
A stable and professional chemical analysis plan ensures that the instrument has a lower detection limit, with a COD detection limit of 4.4mg/L and an ammonia nitrogen detection limit of 0.008mg/L;
• Independently developed quartz colorimetric cell design, small volume and large optical path, ensuring more stable measurement of low values. COD measurement of 20mg/L can ensure accuracy within ± 1mg/L, and NH3-N measurement of 0.2mg/L can ensure accuracy within ± 0.02mg/L;
Software data dynamic analysis technology, automatic chromaticity and turbidity compensation algorithms, algorithms to determine whether chemical reactions are complete, ensuring the accuracy of measurement data;
Pre processing secondary filtration combined with automatic blowback and automatic backwash functions avoids the blockage of pipelines by large suspended particles, ensuring a more stable liquid system;

（4）Easy to operate and powerful in functionality
7-inch true color LED touch screen display, beautiful and elegant human-computer interaction interface;
Humanized module grouping and multi-level user differentiation management software design, making operation simpler;
Intelligent help system, faster to get started, digital concept of instruction manual;
The independent channel automatically checks the standard solution function, which can eliminate instrument reagent faults and quickly locate maintenance and repair fault points;
• Automatic alarm mechanism for data exceeding standards, insufficient reagents, and abnormal operation, with automatic protection and recovery functions for power and water outages;
• Trial dose judgment technology, which can choose float judgment or intelligent calculation method, both have advance alarm function;
Multiple measurement modes, "performance first" and "savings first", ensure the accuracy of instrument measurement;
Built in dilution ratio automatic intelligent switching ensures accurate measurement and meets the needs of a large range;

（5）Data Collection and Control System
Weishui relies on its core technology to build a "data collection system". Based on intelligent instruments, with mobile Internet as the carrier and monitoring and control cloud service platform as the core, we will provide you with more convenient, reliable and professional digital operation and maintenance management services.
Weishui relies on its core technology to build a "data collection system". Based on intelligent instruments, with mobile Internet as the carrier and monitoring and control cloud service platform as the core, we will provide you with more convenient, reliable and professional digital operation and maintenance management services.
Based on Alibaba Cloud high-performance servers, big data collection and alarm system
Can be equipped with a "remote data acquisition and control system" for Wei Shui to achieve remote instrument operation as if in person
• Data backup statistics, alarm status SMS or WeChat push notification function;
• Geographic location of locatable instruments
Multiple system support for mobile app, desktop, web, and iPad

method	Diphenylcarbazide spectrophotometric method
Monitoring scope	(0-10) mg/L Scalable
Display unit	12232 dot matrix display, 7-inch LCD touch screen dual display
Measurement method	Manual measurement, continuous measurement, periodic measurement, fixed-point measurement, automatic calibration measurement, standard solution verification
Measurement period	Adjustable extension from 30 minutes to 24 hours
zero drift	±5% F.S
Span Drift	±5% F.S
repeatability	≤5%
accuracy	±5%
Fault free operation	>720 hours
Store data	Store data for five years
communication interface	4-20mA， RS232，RS485， dry contact
External dimensions	505*395*671（mm）