Comprehensive Analysis of Submersible Level Sensor Types: Structure, Principles, and Application Selection Guide

In industrial automation and process control systems, level is one of the key parameters that directly affect production safety, equipment operation, and product quality. Compared with float switches, radar, and other measurement methods, submersible level sensors are widely used in various level measurement scenarios due to their simple structure, flexible installation, and strong adaptability.

From an engineering application perspective, this article systematically introduces the main types, signal output advantages, working principles, and technical characteristics of submersible level sensors, helping users fully understand their selection logic and application value.

I. What Is a Submersible Level Sensor

A submersible level sensor, also known as a submersible level transmitter, is a pressure-based level measurement instrument that operates according to the principle of liquid column static pressure. By being directly immersed in the measured liquid, the sensor converts the pressure generated by the liquid height into an electrical signal output, enabling continuous level measurement.

Such products typically consist of the following components:

Pressure-sensitive element
Stainless steel isolation diaphragm
Signal conditioning circuit
Waterproof sealed cable

This structural design gives submersible level sensors significant advantages in confined spaces, deep wells, and open water bodies.

II. Main Types of Submersible Level Sensors

According to structural forms and application scenarios, submersible level sensors can be subdivided into multiple types. The following are several representative types commonly used in engineering practice.

General-Purpose Submersible Level Sensor

General-purpose submersible level sensors use diffused silicon pressure-sensitive elements combined with diaphragm isolation technology and are directly immersed in the liquid via a cable.

Their main characteristics include:

Simple structure and easy installation
Reasonable cost control with high cost-effectiveness
Suitable for conventional level measurement scenarios

Typical applications include:

Drinking water systems
Water level overflow weirs
Pump stations, reservoirs, and tanks
Water treatment plants and circulating water systems

This type represents the most widely used basic solution in industrial level measurement.

Split-Type Submersible Level Sensor

Split-type submersible level sensors feature a separated design between the sensing probe and the signal processing unit, making them suitable for applications with high safety and anti-interference requirements.

Their engineering advantages include:

Support for intrinsically safe explosion-proof applications
Probe protection level up to IP68
Lightning protection and radio-frequency interference resistance

They are particularly suitable for industrial sites with flammable or explosive gases and strong electromagnetic interference, such as petrochemical and energy facilities.

Deep-Well Submersible Level Sensor

Deep-well submersible level sensors are specially optimized for large-depth level measurement and are commonly used for groundwater and deep-well water level monitoring.

Their technical characteristics include:

Strong anti-interference capability
Low temperature drift
High long-term stability
Suitable for long-distance cable transmission

They offer irreplaceable advantages in hydrological monitoring and groundwater resource management.

Gas-Collector Type Submersible Level Sensor

Gas-collector type submersible level sensors adopt a gas-guided pressure measurement method and are designed for high-temperature, highly corrosive, or heavily contaminated media.

Their core advantages include:

No direct contact between the sensor and the measured medium
Effective protection of the diaphragm from high temperature and corrosive liquids
Suitable for wastewater, high-temperature liquids, and corrosive chemical media

This structure effectively solves the application challenges faced by conventional submersible level sensors in extreme media conditions.

III. Engineering Advantages of 4–20mA Output for Submersible Level Sensors

In industrial environments, the most common output form of submersible level sensors is the 4–20mA analog current signal.

1. Strong Anti-Interference Capability

Industrial sites commonly suffer from electromagnetic noise and voltage fluctuations. Compared with voltage signals, current signals are insensitive to line resistance changes, and noise currents are typically at the nA level, having minimal impact on measurement.

2. Stable Long-Distance Transmission

Since the internal resistance of a current source approaches infinity, series resistance of the transmission cable does not introduce significant errors. A 4–20mA signal can be stably transmitted over hundreds of meters using ordinary twisted-pair cables.

3. Compliance with Safety and Explosion-Proof Requirements

With 20mA as the upper current limit, the generated spark energy is insufficient to ignite combustible gases, meeting the safety requirements for industrial explosion-proof applications.

4. High Degree of Standardization

As an internationally recognized standard, 4–20mA signals allow seamless integration with PLCs, DCS systems, recorders, and display instruments, reducing maintenance and replacement costs.

IV. Working Principle of Submersible Level Transmitters

Submersible level transmitters operate based on the principle of static pressure measurement.

When the transmitter is immersed to a certain depth in the liquid, the liquid column exerts pressure on the sensor diaphragm, described by the relationship:

ρgh

To eliminate the influence of atmospheric pressure on the liquid surface, the transmitter introduces atmospheric pressure into the negative pressure chamber through a vented cable, achieving automatic compensation.

The comprehensive expression is:

P = ρgh + Po

Where:

P: pressure acting on the diaphragm
ρ: liquid density
g: gravitational acceleration
h: liquid height
Po: atmospheric pressure at the liquid surface

By measuring the pressure value, the liquid level height can be accurately calculated.

V. Core Technical Characteristics of Submersible Level Transmitters

From an engineering application perspective, submersible level transmitters exhibit the following key characteristics:

Use of diffused silicon pressure-sensitive elements with diaphragm isolation for high measurement accuracy
Compact structure with easy installation and maintenance
Anti-clogging and anti-scaling design for long-term operation
Internal temperature and humidity control to enhance sealing and waterproof performance
Support for intrinsically safe and dust explosion-proof applications
Compatibility with remote transmission systems and alarm devices
Protection against reverse polarity, overvoltage, and current limiting

These features make them stable and reliable foundational devices in industrial level measurement.

VI. Typical Application Fields

Submersible level sensors are widely used in:

Municipal water supply and wastewater treatment
Petroleum and chemical industries
Power plants and hydrological monitoring
Reservoirs, dams, and hydropower projects
Environmental monitoring systems

Frequently Asked Questions (FAQ)

Are submersible level sensors suitable for viscous liquids?
Selection should be based on medium characteristics, and gas-collector type structures may be required when necessary.

Does liquid density variation affect measurement?
Yes, density changes affect measurement accuracy and should be considered during parameter configuration or selection.

Is 4–20mA output mandatory?
Not mandatory, but 4–20mA offers significant advantages in industrial environments.

Conclusion

With their simple structure, stable measurement performance, and strong adaptability, submersible level sensors have become an important component in continuous level measurement. Through proper selection of sensor type, output mode, and structural form, various media and operating conditions can be effectively addressed.

As industrial automation continues to advance, submersible level sensors will remain long-term reliable foundational devices in level measurement systems. Nexisense continues to focus on engineering application scenarios, providing a wide range of submersible level sensor solutions to ensure stable operation of level measurement systems.