HM21 Submersible Level Transmitter

The HM21 uses a high-sensitivity silicon piezoresistive element that measures fluid pressure at the sensor tip. When submerged, the hydrostatic pressure (dependent on water depth and density) is converted into an electrical signal proportional to liquid level. The air-venting cable allows atmospheric reference, ensuring accurate depth-independent measurements. No moving parts means excellent reliability and minimal maintenance.

IP68 is the highest ingress protection rating and means the sensor is fully sealed against dust (6) and can withstand continuous submersion in water (8) to specified depths. The “8” specifically indicates protection against immersion beyond 1 meter, which makes the HM21 ideal for underwater level measurement. The junction box on split models has IP65 (water jet protection but not continuous submersion), while the sensor itself maintains IP68.

Integrated (C1): Sensor and amplifier are sealed together in one stainless steel enclosure. The entire unit is submersible, measuring 0–200m H₂O. Ideal for direct throw-in applications with no separate electronics abovewater. Simpler wiring, fewer connection points. Split (C2): Sensor cable connects to a separate junction box on shore/above water. Sensor measures 0–10m H₂O. The remote electronics allow easier adjustment and monitoring. Better for situations where you need the sensor submerged but electronics protected from splash zone. Maximum range is lower than integrated due to cable pressure limits.

Standard cable length is typically 1m to 100m depending on configuration. The Φ7.2mm PVC cable includes an air-venting conduit for atmospheric reference pressure compensation. For integrated models, cable lengths up to 100m+ are feasible. For split models, consider signal attenuation and power loss for very long cable runs. Custom cable lengths and materials (armored cable for harsh environments) are available upon request. Contact our engineers for specific requirements.

±1.0% FS (Code 0): Standard accuracy for general water level monitoring, flood warning, and tank level control. Cost-effective and suitable for most applications. ±0.4% FS (Code 1): Intermediate precision for environmental monitoring, wastewater treatment, and resource management where better accuracy improves efficiency. ±0.25% FS (Code 2): Premium accuracy for precision hydrogeological surveys, dam safety monitoring, and laboratory-grade measurements. Justifies higher cost for critical applications requiring minimal error margins. Select based on your application tolerance and budget. All classes feature excellent long-term stability (±0.1% FS/Year typical).

The standard HM21 features a 316L stainless steel membrane and enclosure, which resists freshwater, wastewater, and most moderate chemical environments. 316L is superior to 304 stainless steel due to higher molybdenum content, providing better saltwater and chloride resistance. For aggressive environments (saltwater, acid, alkali), order the HM21R variant with enhanced corrosion-proof coating (Teflon or epoxy) and upgraded seals. The optional R designation ensures multi-year lifespan even in harsh marine or chemical tank applications. Fluorubber seals provide additional chemical compatibility with oils and solvents.