What is the Working Principle of a Level Transmitter and Level Measurement

Level measurement is the measurement of the level of a fluid, the height of which is known as the liquid level, just like in an oil tank. The measurement of level is crucial in a process, so by doing the measurement, we can ensure the process is safe. The level measurement is categorized into top-down and bottom-up levels. The top-down measurement is not susceptible to leakage or can be considered a less leakage process. The top-down measurement could make contact with the fluid, or sometimes it won’t, while the bottom-up type makes contact with the process fluid. The level measurement is done for more than just fluids. It is likewise used to degree the extent of gases and solids.

Level Measurement Transmitter

Discontinuous Level Measurement

Discontinuous or point level measurement is a technique of measuring the level in a tank or silo by sensing when the level is at some value (point level). Level switches do this for point-level detection.Generally, the control is designed to produce an open or closed contact when a certain point is reached, which can be used for indication and alarm (local or remote).

Continuous Level Measurement

Continuous-level measurement devices measure fluid level in a tank or vessel. They can provide variable point-level detection or alarms. Continuous level measurements are essential for many industries. For example, constant measurement in the water supply industry can control the optimum head pressure in a prominent elevated storage reservoir for proper water discharge pressure and flow to the consumers.

Continuous level measurements are also crucial for storage tanks and silos in industry and power plants to know their inventory levels and control the same. Such measures are also vital for process/mixing tanks/reactors to satisfy process operational requirements, which determine product quality and reliability.

In every process industry, a level transmitter is an important instrument that can prevent overflow or any undesirable condition in the reactor and other vessels. The various types of level transmitters are used based on the process media and process condition. Level transmitters are used for water distribution and storage in a wide range of commercial sectors, including the petrochemical industry, chemical manufacturing and refining units.

To make sure the protection and profitability of the process, the correct stage dimension is mandatory.

Types of Level Transmitters

Regarding level measurement, there are so many different options available in the market. Each type of level transmitter has its advantages and limitations.

Based on the software location and manner of media, stage transmitters are suggested.

Ultrasonic Level Transmitter

Ultrasonic level transmitters are a valuable tool for monitoring the contents of tanks and other vessels. The time of flight principle is used to calculate the speed of sound waves and determine their location. In addition, they are non-contact, meaning they do not need to be connected to the tank or vessel to detect level changes. Instead, they can be installed on top of the tank above the process media, allowing for easy access and visibility of levels within the tank.

The audible frequency of these transmitters is up to 20 kHz. Above this frequency, ultrasonic sounds are transmitted, allowing for the detection of changes in level. This happens continuously as long as an acoustic signal is present—no contact is required!

These devices can provide a local display or output conforming to standard instrumentation signals (e.g., 4 to 20 mA).


  • Measures the actual process temperature at the surface of the process media, providing a more accurate & faster response.
  • It’s more rugged. Once this fails, the device cannot be repaired & must be replaced.
  • Ultrasonic LT can degree as much as 30 M in liquids.

Radar Level Transmitter

Microwave signals are non-contact, so they don’t have to touch the measured object. As a result, microwave technology is suitable for measuring things like powders and liquids, which would be difficult or impossible to do with other measurements.

Microwave signals reflect off a material’s surface, so they travel in a straight line. This is called the time of flight. The amount of microwave reflected depends on the material’s dielectric constant—the higher the dielectric constant, the more electricity it will reflect.

Microwave signals are relatively unaffected by changes in pressure or temperature in the process—they’re accurate even when things are moving fast—and they’re also unaffected by moisture content or other factors that might affect different measurements.


  • It provides accurate readings.
  • It has minimal contact with the substance being measured.
  • It has ease of installation and accessibility.

Hydrostatic Level Transmitter

A hydrostatic level transmitter is a device used to measure liquid levels in pipelines, tanks, vats, and other containers. It works based on pressure measurement, and the working principle of the hydrostatic level transmitter is directly proportional to the height of a vessel containing materials.

Hydrostatic level transmitters are loop-powered and cost-powerful transmitters that degree the liquid stage accurately. The hydrostatic level transmitter is compact and fits perfectly with smaller pipes. Due to its high reliability and robustness, it is prevalent among industries, borewells & tubewells.

Some other technologies are used for special applications like electromechanical type (used in volatile organic storage tanks), capacitance level for food processing applications, magneto-restrictive LTs for flammable fluids, etc.


  • They have a proven measuring principle with high reliability.
  • Hydraulic level transmitters have direct contact with the medium.
  • They provide robust measuring processes, which are unaffected by factors like vapor, contaminants, dust, buildup, foam, etc.
  • The transmitters’ measurement is uninfluenced by characteristics like dielectric coefficient, conductivity, or viscosity.

Level Transmitter Application

Level Measurement in the Soft Drink Industry

Different ingredients are added to process the final product in the soft drink industry. These ingredients need to be maintained at a certain level to achieve acceptable quality and maintain the smooth operation of the assembly line. This is why a level transmitter is used in each storage tank to ensure that the appropriate amount of ingredients is added to get an acceptable product quality. Inventory Management Inventory management is keeping track of inventory in terms of volume or weight level. In custody transfer, accurate measurement of materials is necessary as minute errors would cost more in volume. The device would vary depending on the type of transfer, whether commercial or legal.

Cement Silo Level Measurement

Commercial transferring devices include scales and weighbridges that can be used alone or together. Legal transmitting devices include barcode scanners and radio frequency identification (RFID) tags. In the cement industry, the level transmitters are used to monitor the level of process materials used to manufacture cement and other building materials. For example, in a cement silo, level transmitters help ensure that only the right amount of material is stored at any time to be used efficiently. These devices are also helpful when dealing with other chemicals or liquids that need to be monitored over a more extended period, such as oil refineries or water treatment plants.

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