METER HYDROS 21 Water Level, Electrical Conductivity & Temperature Sensor

Overview

The METER HYDROS 21 is a tri-parameter environmental sensor engineered for high-reliability, long-term monitoring of water level, electrical conductivity (EC), and temperature in shallow groundwater, surface water, wetlands, and estuarine systems. It employs a vented, piezoresistive absolute pressure transducer calibrated to measure hydrostatic head up to 1000 cm H₂O (equivalent to 10 m depth), with integrated barometric compensation to eliminate atmospheric pressure drift—a critical requirement for accurate long-term water level trending. Unlike submersible sensors relying on differential pressure or bubbler systems, the HYDROS 21’s direct-contact design ensures minimal thermal lag and rapid response across its full operating range (−40 to +60 °C). Its compact cylindrical form factor (Ø3.4 cm × 9 cm) enables deployment in narrow monitoring wells (≥5 cm diameter) and confined aquatic microhabitats without compromising structural integrity. Manufactured under ISO 9001:2015 quality management protocols and CE-marked per ISO/IEC 17050:2010, the sensor meets baseline requirements for scientific-grade field instrumentation used in regulatory-compliant hydrological studies.

Key Features

• Tri-parameter measurement: Simultaneous acquisition of water level (0–1000 cm), EC (0–120 dS/m), and temperature (−40 to +60 °C) within a single, sealed housing.
• Vented pressure sensing architecture with real-time barometric correction—enabling decadal-scale water level trend analysis free from atmospheric noise.
• Marine-grade stainless steel and epoxy-encapsulated electronics ensure corrosion resistance in saline, acidic, or organically rich waters.
• Low-power operation: Typical active current draw of 3.5 mA and standby consumption of 0.35 mA supports multi-year deployments on solar-recharged data loggers.
• Dual communication protocols: Native support for both METER’s proprietary DDI serial interface and industry-standard SDI-12, ensuring interoperability with legacy and next-generation dataloggers.
• Modular system design: Signal conditioning, analog-to-digital conversion, and protocol handling reside externally in the datalogger (e.g., ZL6, EM50/60, Campbell CR1000X), reducing sensor unit cost while maintaining metrological traceability.

Sample Compatibility & Compliance

The HYDROS 21 is validated for continuous immersion in freshwater, brackish water, seawater (up to 120 dS/m), and wastewater effluents. Its chemically inert housing and sealed cable junction resist biofouling and chloride-induced pitting. The sensor complies with ISO 9001:2015 for production consistency and carries CE marking per ISO/IEC 17050:2010 for electromagnetic compatibility and safety. While not intrinsically certified for hazardous locations, it meets IP68 ingress protection when properly terminated. For applications requiring audit-ready data provenance—such as EPA Method 1311 leachate monitoring or USGS NWIS compliance—the HYDROS 21 is routinely deployed alongside GLP/GMP-aligned dataloggers (e.g., ZL6 with encrypted SD card logging and time-stamped metadata) to satisfy traceability requirements under 21 CFR Part 11 when paired with appropriate software validation packages.

Software & Data Management

The HYDROS 21 operates natively with METER’s ZL6 Cloud Data Logger, enabling over-the-air firmware updates, remote configuration, and scheduled wireless data retrieval via cellular or LoRaWAN gateways. Raw sensor outputs are delivered in ASCII-formatted SDI-12 or DDI packets, parsed by METER’s PC-based ProCheck software or third-party platforms including Campbell Scientific LoggerNet, Decagon’s Em50 Configurator, and Python-based PySDI12 libraries. All measurements include embedded timestamping, sensor ID, and diagnostic flags (e.g., voltage drop, timeout errors). When integrated into ZL6-based networks, data streams adhere to RESTful API conventions and can be ingested directly into cloud analytics platforms (e.g., AWS IoT Core, Microsoft Azure IoT Hub) for automated anomaly detection, salinity intrusion modeling, or aquifer recharge rate estimation using time-series interpolation algorithms.

Applications

• Wetland hydrology: Quantifying water table fluctuations, evapotranspiration-driven drawdown, and seasonal saturation dynamics.
• Salinity intrusion monitoring: Tracking chloride front migration in coastal aquifers via co-located EC and depth trends.
• Wastewater infiltration assessment: Detecting septic plume expansion through anomalous EC spikes at varying depths.
• Surface water–groundwater interaction studies: Resolving losing/gaining reach behavior using diurnal water level–temperature hysteresis analysis.
• Managed aquifer recharge (MAR) operations: Verifying infiltration rates and subsurface storage volumes via synchronized multi-point HYDROS 21 arrays.
• Educational field labs: Supporting undergraduate hydrogeology curricula with low-cost, maintenance-free sensor nodes scalable to watershed-level deployments.

FAQ

Does the HYDROS 21 require manual barometric pressure input?

No—it incorporates a built-in vent tube that equalizes internal reference pressure with ambient atmospheric conditions in real time, eliminating the need for external barometer integration or post-processing corrections.
Can the HYDROS 21 be used in frozen conditions?

Yes—the sensor housing and electronics are rated for −40 °C operation; however, ice formation inside the vent tube must be prevented via heated enclosures or mechanical vent shielding to maintain pressure equilibrium.
Is calibration traceable to NIST standards?

While the HYDROS 21 ships with factory calibration certificates referenced to METER’s ISO/IEC 17025-accredited standards lab, end-user NIST-traceable recalibration is available through METER’s service center using primary hydrostatic and conductivity reference cells.
What is the maximum recommended cable length for SDI-12 operation?

For reliable SDI-12 communication, cable lengths exceeding 20 m require twisted-pair wiring and termination resistors; METER validates performance up to 40 m using its standard shielded cable with proper grounding practices.
How does the HYDROS 21 handle air entrapment in the pressure port?

The vented design inherently prevents trapped air errors; however, in highly turbulent or aerated flows, mounting orientation (vertical, port-down) and periodic visual inspection of the vent membrane are recommended to ensure unobstructed gas exchange.