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Everything You Need to Know About Level Measurement

In Industry, measuring and keeping a track of all the variables i.e. the process values like temperature, level, pressure, velocity, etc that are constantly changing, is very necessary. In processes such as boilers, there are various factors that affect the value of the main mixture inside the boiler.

large liquid tank

These values are affected by each other as well as the main component of the boiler and vice versa. Now, to maintain these values it is important to measure these values correctly and accurately in a way that can be readable and accessible to the operator.

One of the most important process variables is level. Level indicators indicate the level of solid or liquid inside a closed system. There are various principles by which you can measure level inside a system;

  • Tuning Fork Level Switch: Tuning fork type level measurement uses the principle of tuning fork and harmonics. Tuning forks when vibrated produce harmonics depending upon the size of the tuning fork and the medium they are present in. Thus, they can easily detect the presence, absence, or level of liquid present inside the container. The tuning fork level switch has got a tuning fork-shaped sensing element inserted inside the liquid. It is then set at its natural resonant frequency. When it vibrates but doesn’t produce the same harmonics as it does in free air we know that there is liquid present inside. Or differing harmonics can also detect the level of the liquid present. It is one of the widely used methods of level measurement in the industry.
  • Conductance: The substance present inside the tank or container acts as a dielectric of the two conductance plates. As per the principle of conductance as the quantity of the substance increases between the two capacitor plates the energy or current increases in the circuit. As it decreases the energy decreases too. This principle of conductance can be used to calculate the level of solid or liquid present inside the container. It can also be easily calibrated as the output of this system is current itself and does not need a lot of transduction.
  • Magnetic: In the magnetic type of level measurement, a magnetic object is placed inside a buoyant container and suspended on the liquid. It is then used to detect the level of the liquid present inside. With the float being on the top of the liquid, the magnetic object can measure the level of the liquid present inside. This method is suitable for stable fill as the level of the liquid can be easily transmitted through the magnetic device.  This method is also suitable for solids if you select the right floats.
  • Hydrostatic Pressure: The hydrostatic pressure measurement works on Pascal’s law. According to that law, the pressure of the liquid body in the absence of an external force is a function of itself. This means that the pressure of the liquid is dependent on the type, mass, and quantity of the liquid present. Thus by knowing the pressure of the liquid present inside you can easily calculate the volume of the liquid present inside.
  • Radar Fill: The Radar fill type of level measurement works on the principle of radio wave emission. The suitable radio transmitters are mounted on the top of the container in which the liquid is present. The transmitter sends a signal into the liquid thereby receiving the reflection. The received signal can easily transmit the level of the liquid present inside.
  • Ultrasonic: This is similar to the radar fill type measurement. The only difference being that instead of radio waves, ultrasonic waves are used for knowing the level of the liquid present inside the container.
  • Optical: Optical level detection uses the principle of optical reflection. Inside the container, a LED light is placed and a phototransistor is fitted. When the light is emitted inside an empty container complete light is reflected back to the transistor.

But when it is half filled, some part of the light gets refracted because of the medium. Thus the level of the liquid present inside the container can be detected. The accuracy of optical detectors is very high. Optical level detectors can be used in the detection of any leaks present inside the system.


Thus, we saw several level measuring devices. Level measurement is one of the most common and widely used methods of maintaining and running processes and systems. It is used in both hazardous and non-hazardous mediums.

Even when other types of pressure variables are not calculated, the level is calculated almost in all systems. Different instruments are developed using these basic principles of level detection.

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