Deep Water Submersible Liquid Level Sensor with 0.01%FS Resolution

When the tank is deep, the water column is heavy and small level changes matter, a submersible sensor must do more than simply survive immersion. The QWY-309 delivers laboratory-grade 0.01%FS output resolution, dependable sealing at depth, and a wide -10 to 60 °C liquid temperature range, making it the preferred choice for reservoirs, boreholes, food tanks and marine applications.

Why Do You Need a High-Resolution Deep Water Level Sensor?

Deep installations amplify every measurement error. At 100 meters of water column, a sensor with poor resolution cannot distinguish a 10 cm level change, yet that 10 cm may represent thousands of cubic meters of stored water or the difference between a pump running dry and running safely. Operators of deep reservoirs, groundwater wells and large process tanks need to see small, slow level movements reliably, because inventory accuracy, leakage detection and environmental compliance all depend on it. A high-resolution submersible sensor with stable output resolution of 0.01%FS turns a deep tank into a precise, trustworthy measuring instrument instead of an expensive guess.

Working Principle: Pressure-to-Level Conversion at Depth

The QWY-309 measures the hydrostatic pressure created by the liquid column above its sensing diaphragm and converts it into a linear 4-20 mA signal. Because pressure equals density × gravity × height, the output is directly proportional to liquid depth once the medium density is known. A vented reference inside the cable compensates for atmospheric pressure, so barometric changes never appear as level changes. The sensor is factory-calibrated over its specified range with a resolution of 0.01%FS, and the internal fill fluid transmits the process pressure to the sensing element while protecting it from the measured medium, enabling reliable operation with liquids from -10 °C to +60 °C.

Structural Advantages of the QWY-309

• Deep-rated construction: sealed probe design handles the full 0-25 bar range, equal to about 250 meters of water.
• 0.01%FS output resolution: resolves small level changes even at great depth.
• Wide liquid temperature range: -10 to +60 °C for cold groundwater and hot process liquids.
• Flexible fill fluid options: silicone oil for general service, glyceride-and-water for food and pharmaceutical compatibility.
• IP65 enclosure protection: dependable sealing against moisture in wet installations.
• Standard 24 V DC loop power: simple two-wire wiring to any control system.
• Versatile process connections: 1/2" NPT and NPT1/8 / NPT1/4 thread options.
• DIN43650 plug connection: quick, secure electrical hookup with standard industrial connectors.

Pain Point Analysis: 4 Challenging Working Conditions

Application Cases

Product Advantages

• 0.01%FS output resolution for precise level visibility
• Deep water capability up to 25 bar (approx. 250 m water depth)
• Wide liquid temperature range from -10 °C to +60 °C
• Food-compatible glyceride-and-water fill fluid option
• IP65 enclosure protection for wet environments
• Standard 4-20 mA output with 24 V DC loop power
• 1/2" NPT and NPT1/8 / NPT1/4 connection options
• DIN43650 industrial plug connector
• Vented reference for barometric-error-free readings
• OEM/ODM customization of range, cable and calibration

Technical Parameters

SEO FAQ

Q1: What is the maximum depth this sensor can measure?

The QWY-309 is available with measuring ranges from 0-1 bar to 0-25 bar. Since 1 bar corresponds to approximately 10 meters of water column, the 25 bar version measures water depths up to roughly 250 meters. This covers virtually all deep reservoir, borehole, marine and industrial tank applications. The sensor is factory-calibrated for the exact range you order, and the 4-20 mA output is mapped across that range, so the electronics deliver full resolution over your specific span. If your application requires an unusual depth, contact our engineers and we will recommend the appropriate range and cable configuration.

Q2: What does 0.01%FS output resolution mean in practice?

Output resolution of 0.01%FS means the sensor can resolve a change of one hundredth of one percent of its full-scale range. On a 10-bar sensor, that equals a pressure change of 1 mbar, which corresponds to roughly 1 cm of water level. This level of resolution is essential in deep installations, where a small percentage error represents a large physical quantity. For example, on a 100-meter reservoir, a 0.1%FS error would be 10 cm, while 0.01%FS resolution allows the control system to see centimeter-level movements. High resolution also improves the effectiveness of leak detection and slow-drain monitoring.

Q3: Which fill fluid should I choose for my application?

The QWY-309 can be supplied with silicone oil or a glyceride-and-water fill fluid. Silicone oil is the standard choice for general industrial service: it has excellent thermal stability, low viscosity change over temperature, and good performance across the full -10 to +60 °C range. The glyceride-and-water fill fluid is recommended for food, beverage and pharmaceutical applications where the process medium must not be contaminated by silicone. In the event of a diaphragm rupture, a food-grade fill fluid is far safer for the product. Tell us your industry and medium when ordering and we will match the fill fluid to your process requirements.

Q4: How does the sensor compensate for atmospheric pressure changes?

The QWY-309 uses a vented reference system. A small-bore tube inside the connecting cable is open to the atmosphere at the cable end, so the reference side of the sensing element always sees ambient air pressure. The sensor then measures only the difference between the hydrostatic pressure of the liquid and atmospheric pressure, which is exactly the pressure created by the liquid column. Without this vent, a change in barometric pressure of 30 mbar would appear as a level change of about 30 cm on a water column. The vented design eliminates this error automatically, making the sensor suitable for outdoor and altitude-varying installations.

Q5: What is the operating temperature range of the QWY-309?

The QWY-309 measures liquids with temperatures from -10 °C to +60 °C. This range covers cold groundwater, chilled process liquids and warm industrial media. The upper limit of 60 °C is suitable for most water, wastewater, food and light chemical applications, while the lower limit of -10 °C allows use in cold climates and refrigerated storage areas without the fill fluid thickening excessively. If your process liquid exceeds 60 °C, we recommend discussing a high-temperature sensor variant with our engineers, because the fill fluid and seal materials must be matched to the actual media temperature for long-term reliability.

Q6: Can the sensor be used in potable water systems?

Yes. For potable water service, the QWY-309 can be configured with the glyceride-and-water fill fluid and wetted materials suitable for drinking water contact. The vented cable design prevents contamination of the water by the sensor internals, and the IP65-sealed construction keeps moisture out of the electronics. Potable water tanks, pumping stations and distribution reservoirs are among the most common applications for this sensor. If your project requires specific material certificates or compliance documentation for drinking water contact, please inform us in advance so the correct documentation can be provided with the shipment.

Q7: What process and electrical connections are available?

The QWY-309 offers process connection options of 1/2" NPT, NPT1/8 and NPT1/4 threads, and the electrical connection is a DIN43650 plug connector, the widely used industrial standard that accepts a mating plug with screw terminals. The DIN43650 connector makes installation and maintenance simple: the sensor can be unplugged for testing or replacement without disturbing the field wiring. For applications requiring a different connector, such as M12 or a direct cable gland, custom configurations are available on request. Please specify your preferred connections and cable length when placing your order.

Q8: How is the sensor calibrated and how stable is it over time?

Each QWY-309 is factory-calibrated against traceable pressure standards over its full measuring range before shipment, and the 4-20 mA output is adjusted for linearity at multiple calibration points. The sensor is designed for long-term stability, with an output resolution of 0.01%FS and stable sensing technology that minimizes drift. For most water level applications, re-calibration is only needed after several years of service or after an overpressure event. We recommend an annual verification for critical safety-related installations. Calibration certificates and test data can be provided with each order on request.

Q9: Can the sensor be repaired if the cable is damaged?

In many cases, yes. Because the QWY-309 uses a modular design, a damaged cable can often be replaced or re-terminated at the sensor head rather than discarding the entire instrument. The vented reference tube, however, must be carefully re-connected to preserve atmospheric compensation, so cable repair should be performed by a qualified technician or returned to the factory for service. To minimize the risk of cable damage, we recommend mechanical protection at the wellhead or tank top, proper strain relief, and avoiding sharp bends during installation. Spare cables and connectors are available for maintenance planning.

Q10: What customization and support do you offer for OEM projects?

As the manufacturer, we offer complete OEM and ODM support for the QWY-309, including custom measuring ranges, custom cable lengths, special connector types, custom labels, packaging and documentation. We can also adjust the factory calibration and output mapping to match your control system requirements. With a monthly supply capacity of 100 pieces and delivery within 5-8 working days, we support both prototype quantities and series production. Our engineering team responds to technical inquiries with application-specific advice. Contact us with your specifications to receive a tailored quotation.

Why Choose Our Deep Water Submersible Level Sensor?

The QWY-309 combines true deep-water capability with laboratory-grade 0.01%FS resolution, a wide -10 to +60 °C liquid temperature range and hygienic fill fluid options, so you can standardize on one sensor family for reservoirs, food tanks, marine tanks and groundwater sites alike. Every unit is factory-calibrated, pressure-tested and delivered with the exact range, connection and cable your project needs. Backed by direct manufacturer support, OEM/ODM flexibility and a commitment to on-time delivery, the QWY-309 is the professional choice for engineers who need trustworthy level data from deep, demanding installations.