Ultrapure water must achieve a resistivity of 18.2 MΩ·cm at 25°C — and any deviation signals ionic contamination that can ruin your process. Whether you operate in pharmaceutical manufacturing, semiconductor fabrication, or power generation, continuous online conductivity and resistivity monitoring is non-negotiable. The ERUN-A4K intelligent online conductivity analyzer delivers ±1%FS accuracy with automatic temperature compensation, backed by CE, ISO 9001 and RoHS certifications for worry-free global export.
Resistivity is the inverse of conductivity and the most reliable indicator of ultrapure water purity. While conductivity measures how well electrical current flows through water (in μS/cm or mS/cm), resistivity measures how strongly water resists that flow (in MΩ·cm). For ultrapure water at 25°C, the theoretical maximum resistivity is 18.2 MΩ·cm, equivalent to a conductivity of 0.055 μS/cm.
Any reading above 18.2 MΩ·cm indicates measurement error, while lower readings signal ionic contamination from dissolved salts, metals or other pollutants. This is why laboratory water purification systems display resistivity — the closer to 18.2 MΩ·cm, the purer your water.
An online conductivity analyzer continuously measures ionic contamination by passing electrical current through water between two electrodes. The ERUN-A4K employs a flow-through design with an intelligent sensor that automatically detects temperature and performs real-time temperature compensation — because conductivity readings shift significantly with temperature changes.
The analyzer outputs a standard 4-20mA analog signal for direct connection to PLC or DCS control systems, plus RS485 MODBUS digital communication for data logging and remote monitoring. Powered by DC9~30V with an IP68-rated housing, it withstands pressure up to 4bar and operates across 0.0-60°C.
Parameter | Specification |
|---|---|
Measuring Range | 0-20 mS/cm (K=10.0 cm⁻¹) |
Accuracy | ±1% FS |
Resolution | 0.1 mS/cm |
Temperature Range | 0.0-60°C |
Temperature Accuracy | ±0.5°C |
Temperature Compensation | Auto / Manual |
Output | 4-20mA |
Communication | RS485 (MODBUS-RTU) |
Power Supply | DC9~30V |
Pressure Range | 0~4 bar |
Housing Material | ABS |
IP Rating | IP68 |
Installation | Flow-through (flow cell) |
Source: ERUN-A4K product specifications
Conductivity and resistivity analyzers are essential across pharmaceuticals, semiconductors, power generation, food processing, and wastewater treatment.
Pharmaceutical industry: USP-compliant pure water monitoring for WFI (Water for Injection) and purified water systems
Semiconductor manufacturing: Ultrapure water resistivity monitoring to prevent ionic contamination on microchips
Power generation: Boiler feedwater and condensate monitoring to prevent corrosion and scale formation
Food and beverage: Process water quality assurance
Wastewater treatment: Effluent quality monitoring and process control
Chemical industry: Cooling water and process solution monitoring
Conductivity measurements provide a fast, inexpensive and reliable way to monitor total ionic contaminants in any water treatment system.
CE, ISO 9001 and RoHS certifications are mandatory requirements for exporting water quality analyzers to the EU and global markets. CE certification confirms compliance with EU safety, health and environmental protection standards, covering EMC (electromagnetic compatibility) and LVD (low voltage) directives. RoHS certification ensures the analyzer contains no restricted hazardous substances.
ISO 9001 certification verifies that manufacturing follows internationally recognized quality management systems, with every unit tested before shipping. For international buyers, these certifications eliminate compliance risks and streamline customs clearance — making the ERUN-A4K a turnkey solution for global water quality monitoring projects.
Choose conductivity for general water quality monitoring; choose resistivity for ultrapure water where maximum purity is critical. Conductivity meters measure total dissolved ions and are ideal for cooling water, wastewater and process water. Resistivity meters provide more intuitive performance indicators for high-purity applications — the closer to 18.2 MΩ·cm, the better.
The ERUN-A4K measures conductivity directly and can derive resistivity values through reciprocal calculation, giving you both metrics from a single instrument.
Q: What is the difference between conductivity and resistivity?Conductivity measures how well water conducts electricity (ions present); resistivity measures how well water resists electricity (purity). They are reciprocals of each other.
Q: What resistivity should ultrapure water have?Ultrapure water should read 18.2 MΩ·cm at 25°C, equivalent to 0.055 μS/cm conductivity.
Q: Does conductivity alone guarantee water purity?No. Conductivity/resistivity only measures ionic contamination. It does not detect organic compounds or bacteria.
Q: What output signals does the ERUN-A4K support?Standard 4-20mA analog output plus RS485 MODBUS-RTU digital communication.
Q: Is the ERUN-A4K suitable for outdoor or harsh environments?Yes. IP68 rating and ABS housing provide protection against dust and continuous immersion.
ERUN Group is a trusted manufacturer of intelligent online water quality analyzers with full CE, ISO 9001 and RoHS certifications — delivering high-stability, high-precision instruments to industries worldwide.
Learn More:ERUN-A4K Intelligent Online Conductivity Analyzer
