Difference between level measurement in open and closed tanks

In open tanks, the liquid level is most often measured in relation to atmospheric pressure. In this case, the hydrostatic pressure of the liquid is directly proportional to the depth of the liquid. In closed tanks, the situation is more complicated, because the pressure inside the tank is not constant and can vary from atmospheric pressure. Therefore, in this case, level measurement must take into account both the hydrostatic pressure of the liquid and the pressure inside the tank.

Level measurement methods in closed tanks

• Hydrostatic level measurement (pressure measurement): The most common method, measuring the hydrostatic pressure at the bottom of the tank taking into account the pressure of air or gas above the liquid. Differential pressure transmitters, such as the JUMO dTRANS p20 DELTA, are ideal for this purpose.

• Float measurement: Uses a float that rises with the changing level of the liquid and transmits level information to the transmitter. Transmitters in the JUMO NESOS series are an example of such devices.
• Ultrasonic and radar measurement: These methods involve sending out waves (ultrasonic or radio waves) and measuring how long it takes for them to reflect off the surface of the liquid.
• Capacitive measurement: Uses changes in electrical capacitance between electrodes immersed in a liquid as the level changes.

Each of these methods has its own advantages and limitations, so it is important to choose the right technology depending on the specific application and tank conditions.

Measuring the level in closed tanks using a differential pressure transmitter

A differential pressure transmitter, such as the JUMO dTRANS p20 DELTA, works on the principle of measuring pressure differences. In closed tanks, this measurement refers to the hydrostatic pressure of the liquid and the pressure inside the tank. By calculating the difference between them, which is proportional to the height of the liquid column in the tank, the transmitter is able to accurately determine its level. It is important to consider the appropriate installation location of the pressure transmitter to avoid areas with large fluctuations in pressure or temperature.

In the case of measurement using a differential pressure transmitter, two measuring points are required:

Lower capillary: Placed at the bottom of the tank and measures the total pressure of the liquid column.

It consists of two simultaneous pressures:

• Pressure caused by the depth of the liquid (hydrostatic pressure).
• Internal pressure of the tank, which can be caused by various factors, such as fermentation processes.

Upper capillary: is placed where there is no direct contact with the liquid, so it only measures the internal pressure of the tank, without considering the hydrostatic pressure of the liquid.

In summary, to determine the actual level of liquid in the tank, we need to know the difference between the pressure measured at the lower measuring point and the pressure measured at the upper measuring point. This difference corresponds to the hydrostatic pressure of the liquid, which is proportional to its depth in the tank.

Measuring liquid level in closed tanks using float-type liquid level sensors

The JUMO NESOS series level transmitters are designed for continuous, precise measurement of liquid levels in various applications, including closed tanks. They operate on a float principle, based on Archimedes' law, where the float moves along a guide as the liquid level changes. Floats of various shapes are available, made of stainless steel or titanium.

Float-type level indicators from the JUMO NESOS series, such as JUMO NESOS R04 and JUMO NESOS R40, are available in curved or horizontal versions and can be mounted sideways, which is particularly useful in closed tanks with limited top access.

In potentially explosive environments, such as gasoline tanks, it is important to use technology with appropriate safety certifications. Float-type level meters from the JUMO NESOS series have Ex certifications, meaning they can be safely used in explosion-prone areas.

In summary, the JUMO NESOS series level transmitters are versatile tools for measuring levels in closed tanks, offering installation flexibility, safety in explosive environments, and the ability to simultaneously measure level and temperature. JUMO NESOS float level probes are designed to withstand pressures from -1 to 37 bar, making them ideal for use in pressure tanks. During installation, it is important to ensure that the float is placed in a location that allows free movement up and down.

How to measure the liquid level in a closed tank? Summary

Measuring the liquid level in closed tanks is a key element of many industrial processes. In this article, we have presented two main approaches to monitoring the level in such tanks: using the JUMO dTRANS p20 DELTA differential pressure transmitter and the JUMO NESOS series of float liquid level sensors.

The JUMO dTRANS p20 DELTA differential pressure transmitter is able to accurately determine the filling height based on the measurement of the hydrostatic pressure (so-called liquid column) and the internal pressure of the tank. On the other hand, the level transmitters of the JUMO NESOS series, which operate on the float principle, are ideal for tanks with limited access from above and in environments with a potential risk of explosion. Their versatility, safety and precision make them an excellent choice for many industrial applications.

Choosing the right measurement method depends on the specific application, operating conditions and accuracy and safety requirements. Both differential pressure transducers and float liquid level sensors have their own unique advantages that make them suitable for different scenarios in closed tanks. The final choice depends on the individual needs and specifics of the application and the medium being measured. Contact us - we can help you choose the right method and measuring equipment!

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