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Hydrostatic level transmitters are devices that determine the liquid level in tanks by measuring pressure. As the liquid height increases, the hydrostatic pressure at the tank bottom rises. This pressure is measured by the transmitter and converted into an electrical signal to provide continuous level monitoring. They are widely used in applications such as water, chemicals, and food production.

WORKING PRINCIPLE

The principle is based on the hydrostatic pressure exerted by the liquid column.

Formula: P = ρ × g × h

Where:
P: hydrostatic pressure (Pa)
ρ: liquid density (kg/m³)
g: gravitational acceleration (9.81 m/s²)
h: liquid height (m)

The transmitter at the bottom of the tank measures this pressure, processes it electronically, and converts it into level information.

STRUCTURAL FEATURES

Pressure sensing elements: piezoresistive or capacitive diaphragms
Body materials: stainless steel, titanium, PVDF
Output signals: 4-20 mA, HART, Modbus
Protection class: IP67–IP68
Temperature compensation for density variations

ADVANTAGES AND LIMITATIONS

Advantages:

High accuracy (±0.1%)
Unaffected by foam, vapor, or dust
Reliable performance in deep tanks
Continuous measurement capability

Limitations:

Density variations may cause errors
Not suitable for solid materials
Risk of diaphragm clogging
Requires periodic calibration

SELECTION CRITERIA

Type and density of the liquid
Tank depth and pressure range
Mounting type (submersible, flanged, threaded)
Environmental conditions (temperature, chemical resistance)
Required communication protocols and integration

APPLICATION AREAS

Water and wastewater treatment plants
Chemical and petrochemical industries
Food and beverage production
Power plants (cooling water reservoirs)
Agriculture and irrigation systems

STANDARDS

IEC 61298 (pressure devices)
ATEX & IECEx certifications (for explosive atmospheres)
EHEDG (hygienic design – food sector)

CONCLUSION

Hydrostatic level transmitters are among the most widely used level measurement devices in industry due to their reliability and accuracy. With proper selection and regular maintenance, they can operate flawlessly for years while enhancing process safety.