HM21F Lightning Protected Level Transmitter

Class III lightning protection indicates the highest rated protection level for measuring instruments. The HM21F is rated for 10,000V surge voltage and 5,000kA peak current protection (with optional 20,000V/10,000kA upgrade). This advanced patented lightning protection device safeguards the internal electronics and sensor from direct and indirect lightning strikes, making it ideal for thundering regions where electrical surges could damage conventional transmitters. The protection ensures continued operation during severe weather events when accurate water level monitoring is most critical.

The HM21F is based on the proven HM21 submersible level transmitter platform but adds a patented lightning protection device integrated throughout the entire unit. Both models share the same measurement principle (hydrostatic pressure), accuracy specifications (±0.25%, ±0.4%, ±1%FS options), depth rating (up to 200m), and ordering code structure. The key difference is that the HM21F is built-in with Class III lightning protection (10,000V/5,000kA standard or 20,000V/10,000kA optional), making it specifically designed for thundering areas and mountain regions. If your application does not involve risk of lightning strikes, the standard HM21 offers equivalent performance at a lower cost.

Yes, the HM21F supports 12V battery operation for field applications without access to stable AC power supplies. The 12-36V DC power supply range makes it compatible with standard automotive batteries or portable solar power systems. This is particularly valuable for remote monitoring stations in mountainous areas where electrical infrastructure is limited. The lower power consumption of the sensor allows for extended field deployment. For continuous operation or high-frequency data transmission, we recommend evaluating battery capacity requirements with our technical team to determine the optimal power solution for your specific application.

While the HM21F provides Class III lightning protection for the transmitter itself, proper installation practice includes: (1) Using shielded cable (typically Φ7.2mm PVC) to minimize electromagnetic interference, (2) Installing surge arrestors on the signal lines at the control building for additional system-level protection, (3) Ensuring proper grounding of the transmitter enclosure to dissipate electrical charge, (4) Keeping signal cables away from power lines and equipment that may generate electrical noise, (5) Using lightning rods or surge protection devices on nearby infrastructure. The HM21F’s protection device protects the internal circuitry, but comprehensive system protection requires coordination with your site’s grounding and surge protection design. Consult our technical team for site-specific installation recommendations.

The HM21F has a maximum depth rating of 200 meters (0~200m H₂O range). The IP68 protection rating indicates the highest level of ingress protection: the “6” means dust-tight (no dust can enter), and the “8” means the device can be fully submerged continuously in water. Specifically, IP68 means permanent submersion is possible without water entering the enclosure or affecting internal electronics. The stainless steel construction (SS 1Cr18Ni9N enclosure, 316L sensing membrane) and fluorubber seals provide excellent corrosion resistance in fresh water, salt water, and other aqueous environments. The 200m depth corresponds to approximately 2MPa pressure, making it suitable for deep water applications in lakes, reservoirs, and river systems.

The HM21F offers three accuracy tiers to match your application requirements: ±0.25%FS (highest precision) for critical measurement applications requiring maximum reliability and detailed data logging, ±0.4%FS (medium precision) for general water level monitoring and flood warning systems where good accuracy is needed but extreme precision is not essential, and ±1%FS (standard precision) for budget-conscious installations where basic level indication is sufficient. Choose based on your control system requirements and regulatory standards. For hydro-power plants or water treatment facilities, ±0.25% is recommended. For flood forecasting and general water conservancy, ±0.4% typically provides the best balance of cost and performance. The ordering code includes your accuracy selection (0 = ±0.25%, 1 = ±0.4%, 2 = ±1%).