Level Sensor (definition and working principle)

Explore all about the Level sensors.

A level sensor plays an important role in any industrial field. It is an essential component of the automation and control systems to enhance, optimize, and get the maximum performance of any process. It also ensures the process’s highest safety factors for humans and equipment.

Level Sensor

 
In this article, we will discuss everything about the level sensors in the instrumentation system such as the meaning, function, types, and applications of the level sensors. Join us and let us start.

What is a level sensor?

A level sensor is a device (mechanical or electrical based on the type) used to convert the physical level or volume of different materials (liquid, powder, or water) to a monitored value used in many Industrial processes’ applications such as oil and gas, and renewable energy.

What is the function of level sensors?

Level sensors are used in the system ​​to monitor the material level, and protect equipment from overflow or material shortage. It controls the filling process of any material by increasing or decreasing the filling quantities based on the level sensors’ reading.

How does a leveling sensor work?

The level sensor is installed at the field level and close to the equipment and converts the material level into an electrical signal. This feedback signal from the level sensor is connected directly to the hard wire of the PLC and transferred to the higher control level (PLC) in the automation pyramid.

What are the Types of level sensors?

When we explore the type of level sensors, we have to classify the types according to some concepts. These categories are represented based on the contact with materials, working principles, and output signal type.

1- Contact Level Sensors.

It is the type where the level sensor is physically in contact with the measured material. This category is simple and has a cost impact but some parameters should be considered such as measured material level specification to minimize the material hazards and corrosion.

Examples of contact level sensors are listed below such as:

• Float Sensors. Where a floating object is used to fall or rise according to the material level. This sensor is suitable for measuring the water in tanks and oil reservoirs. It is reliable and simple. It has a lower cost compared to other types. The disadvantage of that example is that it is used with clean liquids and materials have low viscosity.
• Resistance Tape Sensors. It measures the change in level based on the change that happens according to the change in resistance. the resistance resistance is converted to an electrical signal representing the tank level. This type is good for measuring the fuel level of fuel tanks where the precis exists.
• Capacitive Sensors. It uses the concept of changing the capacitance caused by the absence or presence of the measured materials. It is suitable for measuring the chemical materials in tanks and the level in grain silos. It is good for measuring solid and liquid materials but is affected by moisture and temperature changes.
• Conductive Sensors. It uses the material’s electrical conductivity to detect the level of liquid materials. It is suitable for wastewater and water treatment. It is good for the conductive material but cannot be used with non-conductive materials.

2- Non- Contact Level Sensors

In this non-contact, level sensors operate without direct contact with the material. They are ideal for applications where hygiene, corrosiveness, or high temperatures are concerns. Many sensors work according to that concept.

Examples of non-contact level sensors are listed below such as:

• Radar Sensor. It uses the radio and microwave reflected radiation from the material surface and conditions it to an electrical signal representing the filled and empty parts of tanks. It is good for both high pressure and temperature. It is accurate and has no bad impact on the environment. But it costs a lot of money.
• Ultrasonic Sensors. It sends ultrasonic waves and receives them again after reflected from the material surface, it calculates the time to receive the reflected waves. The time and the speed of the wave determine the material level in the tanks.
• It is an accurate and reliable sensor suitable for many industrial processes such as cement, chemical industries, and water tanks. It has the advantage that is suitable for many types of materials but cannot be used with foam, temperature, or turbulence.
• Laser and light sensors. They are using the same concept of sensing a laser or light in tanks and receiving the reflected waves from the surface of the materials. Based on the time between sender and receiver, they determine the level of the materials inside the tanks. They are accurate and high precision. But it is expensive and affected by dust.

3- Specialized Level Sensors

These sensor types are designed and used with specific and special processes as well as some applications are not suitable to work with the previous types of sensors. It uses the effect of other physical quantities like pressure and load to represent the load.

Examples of Specialized Level Sensors are listed below such as:

• Hydrostatic Pressure Sensors. It measures the extracted pressure from the material and converts it to level measurement. It is good for underwater applications and large tanks. It works with many depths but is affected by the change in density.
• Load Cell Sensors. In this type of sensor, the load cell measures the weight of the material in the tank and calculates the level of the material based on that weight. It is good with bulk material measurements. It is reliable and accurate but it needs calibration and more steel structure.

load cell for level measurement

• Diaphragm Sensors. In this type, the material pressure affects the diaphragm and changes its position. The change in the position is measured and converted to a signal representing the material’s level. It is good for the grain, bulk, and sand materials. It is robust, easy, and simple.

4- Level Sensor signals. 

In this type, the level sensors are classified based on the type of output signals (digital and analog) sent to the system. The analog level sensors produce a continuous measurement and the digital sensor produces only two statuses of level. OK or not OK.

In summary, level sensors are mechanical or electrical devices that enhance, control, and optimize any industrial process. Many types of sensors are classified based on their direct contact with the material, based on the type of output signals, and finally, based on the application that uses the level sensors.

In the coming articles, we will discuss more about level sensors explaining the advantages, disadvantages, and applications of the level sensors. We will also explain some examples of level sensors in detail to learn more about level sensors.