Level

A submersible liquid level transmitter is an industrial instrument that measures liquid level based on the hydrostatic pressure principle. Its core sensing element is either a diffused-silicon pressure sensor or a ceramic capacitive pressure sensor. The probe is directly submerged in the liquid and converts the hydrostatic pressure at the sensing element (P = ρgh) into an output signal, such as 4–20 mA or an RS-485 digital output. This pressure is proportional to the liquid density and liquid level height. After temperature compensation and linearization by the built-in circuit, the liquid level depth can be accurately calculated. Its structure typically consists of a probe made of stainless steel, PP, or PVDF, a vented cable, and a transmitter module. The vented cable introduces atmospheric pressure to the sensor reference end, thereby eliminating the influence of atmospheric pressure variations on measurement. The submersible liquid level transmitter is easy to install and offers high measurement accuracy, making it an indispensable fundamental measurement unit in industrial automation systems.

• ±0.1%F.S. high-precision liquid level measurement, enabling precise process control
• Robust and durable, suitable for industrial environments, resistant to corrosion and high temperatures, and capable of use in harsh environments.
• Simple structure, high reliability, and low maintenance cost
• Flexible integration with multiple output options for easy automation system integration.
• Widely used in the chemical, petroleum, pharmaceutical, and water treatment industries.
• Cone-plug sealing design, designed to resist sludge buildup and clogging

PP Material

Good corrosion resistance and cost-effectiveness, with good tolerance to most inorganic acids, alkalis, and salt solutions. Suitable for medium-corrosion environments such as general acid-base solutions and industrial wastewater treatment. However, it should be noted that its tolerance to strongly oxidizing acids such as concentrated sulfuric acid and nitric acid, as well as some organic solvents, is limited..

PVDF Material

Known for its excellent chemical stability, it can effectively resist the erosion of highly corrosive media such as strong acids and strong alkalis. It is a reliable choice for liquid level monitoring of corrosive liquids in fields such as chemicals and environmental protection. Its temperature resistance is superior to PP material, and it offers high long-term stability. It is widely used in harsh working conditions such as chemical storage tanks, acid-base neutralization pools, and sewage treatment.

SUS316 Stainless Steel

With excellent mechanical strength, corrosion resistance, and high-temperature resistance, the addition of molybdenum enhances its resistance to chloride corrosion. It is an economical and reliable choice for industrial water treatment and general chemical applications. It is suitable for scenarios such as seawater, mild acid-base solutions, and petrochemical process liquids. It is sturdy, durable, and easy to install.

 

Polyurethane Cable

Excellent wear resistance and tear resistance. It is not easily damaged during long-term use in liquids containing sand and particles. It also offers good oil resistance, hydrolysis resistance, and UV resistance, making it suitable for long-term immersion applications in outdoor and humid environments. This material has outstanding flexibility with a small cable bending radius, making it easy to install and route in confined spaces such as deep wells and water pools. It is the most commonly used economical cable option.

 

PTFE Cable

It has extremely strong chemical inertness and is virtually immune to erosion by any acid, alkali, salt solution, or organic solvent. It is the preferred cable material for liquid level measurement in highly corrosive media. Meanwhile, PTFE has an extremely low surface energy and excellent hydrophobicity. Water vapor cannot adhere to or penetrate the pipe wall, effectively keeping the interior of the vent tube dry and unobstructed, ensuring long-term stability of pressure transmission. Its wide temperature resistance range makes it suitable for harsh working conditions such as chemical storage tanks and acid-base neutralization pools.

Transmitters

Clarify Measurement Type and Range Parameters

Understand the measurement principle

• The submersible liquid level transmitter is based on the hydrostatic pressure principle. It measures the difference between the static pressure of the liquid at the probe position and atmospheric pressure. It is suitable for open containers or atmospheric pressure water pools connected to the atmosphere.

Range selection

• Select the range based on the actual maximum liquid level height. The normal working value should fall within 30%~70% of the range. The range should be slightly larger than the actual maximum liquid level value to reserve margin for fluctuations. For pressurized containers or working conditions with large liquid level fluctuations, confirm the overload pressure margin (typically 1.5 times the rated pressure).

Installation depth confirmation

• The probe must be fully submerged, with a submersion depth greater than 50mm, to avoid probe exposure during liquid level fluctuations. At the lowest liquid level, the probe should still be submerged. At the highest liquid level, it should not exceed the upper range limit.

Determine the accuracy class

• For general water treatment, class 0.5 can be selected. For high-precision control or metering applications, class 0.2 or better can be selected. Note that high precision typically has a minimum range requirement (e.g., ≥10m).

Confirm whether it is for a closed container

• The submersible liquid level transmitter measures gauge pressure and is only suitable for open containers or containers connected to the atmosphere. Closed pressurized containers are not suitable for direct submersible measurement.

Measured Medium and Wetted Parts Material (Core)

Confirm medium properties

• Whether the liquid is corrosive, viscous, prone to crystallization, contains solid particles, or prone to scaling. Medium density is a key parameter for hydrostatic pressure measurement, and density changes directly affect measurement accuracy.

Probe material selection

Viscous, crystalline, and slurry-containing media

• The probe may become clogged or scaled. A probe with anti-clogging design or an added filter device should be selected. For extremely viscous media, it is recommended to use non-contact measurement instruments.

Food/pharmaceutical sanitary applications

Select a sanitary probe with a polished wetted surface. The connection method should comply with sanitary standards.

Temperature Conditions (Medium Temperature + Ambient Temperature)

Output Signal and System Matching

• Standard industrial applications: 4-20mA two-wire, strong anti-interference capability, long transmission distance.
• Digital system: When networking or remote communication is required, select RS485 (Modbus-RTU) digital output.
• Voltage output: 0.5-4.5V is suitable for specific acquisition modules.
• Confirm cable distance: Long-distance signal transmission requires evaluation of signal attenuation. Shielded cable is recommended, with the shield layer reliably grounded.

Explosion Protection, Protection Rating, and Site Environment

Flammable and explosive hazardous areas

• Strictly confirm the explosion protection grade. Intrinsically safe Ex ia or flameproof type must match the site area classification. Ordinary non-explosion-proof types cannot be used in explosion-proof areas.

Protection rating

• The probe is recommended to be IP68 (capable of long-term immersion).

Vibration applications

• For locations with high vibration, confirm the anti-vibration specifications of the transmitter. Wrapping steel wire around the probe for shock absorption can prevent cable breakage.

Electromagnetic interference

• Keep away from high-power motors, transformers, and other strong electromagnetic interference sources to prevent signal abnormalities.

Process Connection, Cable, and Accessory Selection

Installation Position and Maintenance (Special Dedicated Points)

• Keep away from disturbance zones: The installation point should be away from pumps, valves, agitators, and other equipment prone to turbulence and bubbles. If unavoidable, a stilling tube or buffer device should be added.
• Foam and suspended solids on the liquid surface: When there is a large amount of foam, suspended solids, or sediment on the liquid surface, a probe with anti-clogging design should be selected, or a filter screen should be added.
• Probe installation angle: Install vertically or at an incline (inclination angle not exceeding 30°). Avoid horizontal placement, which can cause sediment to accumulate on the sensing surface.
• Regular cleaning and calibration: Long-term immersion of the probe will cause impurities and biofilm to attach, affecting pressure transmission. Regular cleaning is recommended. The calibration cycle is generally every 3~6 months or once a year.
• Zero point verification: Before installation, verify the zero point output (4mA) in a no-liquid state, and verify the full-scale output (20mA) at full scale to ensure measurement accuracy.

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