Types of Level Sensors and Their Differences

Level sensors have been widely used in the market for many years, covering industries such as food and beverage, industrial, medical, printing, agriculture, automotive, and white goods. They are used for leak detection or liquid level measurement. So, what exactly is a level sensor? In this article, we will introduce several common types of level sensors (also known as level switches), along with their characteristics and differences.

What is a Level Sensor?

A level sensor is a device used to measure the height of liquid or fluid levels within a container. They can measure the water level in a tank, the oil or fuel in a storage tank, or the liquid level in a chemical container. These sensors come in various types and can measure liquid levels in different ways. These level sensors or level switches can be used to monitor changes in system liquid levels, as well as trigger alarms or automatically shut off valves when the level is too high or too low.

Types of Level Measurement Methods

Why might customers choose one type of level sensor technology over another? Sometimes, equipment manufacturers may be surprised by the diversity and intelligence of level sensor technologies. There are many types of level sensors, and some common technologies include:

Optical Level Sensors

Optical level sensors are single-point level sensors that use a light source and detector to monitor the liquid level.

Advantages: Compact, no moving parts, high pressure and temperature resistance, small size, capable of detecting small amounts of liquid, strong compatibility. Suitable for small configurations like stirring tanks.

Disadvantages: Intrusive, must be in contact with the liquid; requires power support; certain viscous substances may cause a buildup of coatings on the prism.

Applications: Suitable for level measurement, dry run prevention, overflow protection, and leak detection, capable of indicating the presence of liquid.

This type of sensor uses terms such as optical prism, electro-optical, single-point optical, and optical level switch. In this application, we use the term “optical level switch,” which works by using LEDs and phototransistors. When the sensor tip is in air, light is reflected back to the detector; when the sensor touches the liquid, light is refracted, causing a reduction in the light received by the detector. This solid-state device is ideal for point-level detection applications, especially where high reliability is required. Optical level switches are widely used in tanks of different sizes for high, low, or intermediate-level detection, and are suitable for leak detection to prevent expensive damage.

Vibrating Level Sensors (Tuning Fork)

Tuning fork vibrating level sensors are contact-type sensors that detect liquid level changes through frequency changes in a vibrating element.

Advantages: Compact, cost-effective.

Disadvantages: Intrusive, limited number of uses.

Applications: Suitable for level control of liquids, powders, and fine granular solids, widely used in mining, chemical, food, and beverage industries.

Tuning fork sensors are ideal for controlling the level of both solids and liquids, especially for viscous materials, foam, powders, and fine granular solids. However, their application is generally limited to “overfill” or “dry run” monitoring, rather than continuous process measurement. They can be combined with other continuous level detection systems for overfill and leak alarm points.

Ultrasonic Level Sensors

Ultrasonic level sensors are non-contact sensors that determine the liquid level by measuring the distance to the liquid surface.

Advantages: No moving parts, compact, reliable, unaffected by medium properties.

Disadvantages: Higher cost, intrusive, performance may be affected by environmental factors. The sensor typically has a dead zone nearby.

Applications: Suitable for non-contact applications, especially for measuring high-viscosity and bulk solid materials, also suitable for systems requiring remote monitoring.

Ultrasonic level sensors work by emitting high-frequency sound waves and calculating the time it takes for the sound waves to reflect back to the sensor. The time it takes for the sound wave to return is proportional to the distance to the liquid surface. Environmental factors such as turbulence, foam, or temperature changes may affect the sensor’s response time, so the installation position is critical.

Float Switches

Float switches are contact-type sensors that measure the liquid level by the rise and fall of a float.

Advantages: No power required, direct indication, relatively low cost, multiple output options.

Disadvantages: Intrusive, moving parts, larger in size, the float must contact enough liquid to function, not suitable for liquids with significant fluctuations.

Applications: Widely used for detecting liquid levels in tanks containing water, oil, hydraulic fluids, and chemicals.

Float level switches are a very economical and mature water level detection technology. They work through the interaction of magnets inside the float and an external magnetic reed switch, which operates when the liquid level changes. Common installation methods include horizontal/side mounting and vertical mounting, depending on the design of the tank or container.

Capacitance Level Sensors

Capacitance level sensors detect liquid levels by measuring changes in the capacitance between two electrodes.

Advantages: Solid-state, can be non-contact, compact, accurate, provides variable level measurement.

Disadvantages: May require calibration, only suitable for certain liquids.

Applications: Widely used for level monitoring in industries such as chemicals, food, water treatment, power, and brewing.

Capacitance level sensors are suitable for various solids, liquids, and mixtures. They offer both contact and non-contact configurations, with some versions designed for external installation on containers. It is important to note that not all capacitance sensors are suitable for all types of materials or containers. Since this technology is contact-based, liquid adhesion to the probe may affect sensor reliability.

Radar Level Sensors

Radar level sensors are non-contact sensors that measure liquid levels using radar technology.

Advantages: Highly accurate, no calibration required, offers various output options.

Disadvantages: Expensive, may be affected by environmental factors, limited detection range.

Applications: Suitable for environments with moisture, steam, and dust, particularly systems with significant temperature fluctuations.

Radar sensors work by emitting microwave signals and measuring the time it takes for the signals to reflect back to the sensor. By calculating the return time, the liquid level can be determined. Radar technology provides highly accurate level information and can compensate for fixed structures inside the container. It performs well in foam and viscous materials.

Conductivity Level Sensors

Conductivity level sensors are contact-type sensors that detect liquid levels based on changes in the liquid’s conductivity.

Advantages: No moving parts, easy to use, relatively low cost.

Disadvantages: Intrusive, the liquid must have certain conductivity, probe may corrode.

Applications: Suitable for level detection in boiler water, reagent monitoring, and highly corrosive liquids.

Conductivity sensors are used to detect the level of conductive liquids (such as water and highly corrosive liquids). They consist of long and short probes, where the long probe transmits low voltage, and the short probe’s tip is at the switching point. When the liquid contacts both probes, current flows between them, activating the switch. Due to the low voltage and current used, they are relatively safe. They are also easy to install and use, but the probes need to be regularly checked to prevent buildup from affecting performance.

Differences in Level Measurement Methods

The main differences between these sensors lie in the way they detect liquid levels. Ultrasonic and radar sensors are non-contact technologies, meaning they do not come into direct contact with the liquid being measured. Meanwhile, optical, float switches, and conductivity sensors are contact-based and require the sensor to be in direct contact with the liquid．