Measuring liquid levels in open and closed tanks

Measuring liquid levels varies considerably depending on whether one is dealing with an open or closed tank. In open tanks, where the liquid is exposed directly to atmospheric pressure, the measurement process is usually simpler and may use more direct methods such as float level sensors or hydrostatic probes. In contrast, in closed tanks, where the liquid is under additional pressure or isolated from the environment, more advanced technologies such as differential pressure transducers are required. These differences are driven by the need to adapt measurement methods to the specific conditions of the environment. It is crucial to consider the specifics of each application, as accurate liquid level measurement is essential to ensure process efficiency, safety and optimised asset management.

How to measure level in closed tanks?

Hydrostatic probes can be used to measure the level in closed tanks, but they need to be adapted to the conditions in such tanks.A hydrostatic probe measures the pressure exerted by a column of liquid, and this pressure is proportional to the height of the liquid above the sensor.In closed tanks, it is important to take into account any additional gas or vapour pressure that may be above the liquid, which can affect the accuracy of the measurements.

In addition to hydrostatic probes, there are several other methods of measuring liquid levels in closed tanks that may be better suited to specific conditions, such as differential pressure transducers.

Do the volume and dimensions of the tank affect the level measurement?

The answer to this question is complex and depends on the measurement method chosen. For open tanks, where the influence of atmospheric pressure is constant and unchanging, the shape and dimensions of the tank are the main factor affecting the measurement. For example, in tanks with unusual shapes, such as conical or cylindrical, calibration of the sensor may be required to account for the changing geometry.

Conversely, in closed tanks, where pressures other than atmospheric pressure may exist above the liquid, the volume of the tank may be less important. In such cases, it is more important to consider the gas or vapour pressure above the liquid, which may influence the choice of appropriate measurement technology, such as differential pressure transducers or float level indicators.

Overall, both the volume and dimensions of the tank can affect the measurement of liquid levels, but it is key to understand that each case requires an individual approach and potentially different measurement methods to ensure the highest accuracy.

Hydrostatic probes

The hydrostatic probe is one of the most basic, yet reliable methods of measuring the level of liquids in tanks. Its principle is based on the law of hydrostatics, according to which the pressure exerted by a liquid at a certain depth is proportional to the height of the liquid column above that point. In other words, the higher the level of the liquid in the tank, the more pressure it exerts on the bottom or on the sensor located there. A hydrostatic probe measures this pressure, converting it to a value corresponding to the height of the liquid.

Hydrostatic probes are widely used in various industrial sectors because of their versatility and their ability to withstand a wide range of environmental conditions. They are used in both small tanks and large industrial installations. In the water and wastewater industry, they are used to monitor water levels in storage tanks, reactors, wells and wastewater treatment plants. In the chemical and petrochemical industries, they are used for precise level measurement of a variety of substances, from aggressive chemicals to crude oil.

Capacitive Level Limit Switches

Capacitive level limit switches, such as the JUMO ZELOS C01 LS, play an essential role in various industrial sectors, offering precise and reliable solutions for monitoring the level of liquids and bulk materials. This type of sensor measures the point level of media, which is crucial in preventing overflow and dry running, for example, in pumps. Its applications are diverse and include the food and beverage industry, rail technology, shipbuilding, mechanical and plant engineering, as well as water and sewage engineering. Their durability under high pressure and temperatures, and their ability to operate in hygienic environments and explosion-hazard zones make them versatile and safe to use.

Capacitive level sensors as an alternative to radar level sensors

Capacitive level indicators are an attractive alternative to radar level sensors, especially in applications where simplicity, cost-effectiveness, and minimal maintenance are priorities. Although radar sensors are valued for their accuracy in challenging conditions, capacitive indicators offer lower costs and are less sensitive to foam or contamination. They are ideal for precise measurements in small tanks and where the presence of vapors is minimal. Additionally, their simplicity and fewer moving parts often make them more reliable in long-term use, which is key in industrial applications where long-term stability and minimal maintenance are priorities. The choice between these two liquid level sensor technologies should depend on the specific requirements of the process, allowing for the optimization of both performance and costs.

Float level sensors

Float sensors, used to monitor liquid levels, work on the principle of a floating float that moves with changes in the liquid level. They are simple, reliable and widely used in many industrial applications. The JUMO NESOS series of float transmitters further develops this technology by introducing advanced features such as precision magnetic mechanisms and reed switches for multi-point switching. These enhancements make the NESOS series of level probes more flexible and suitable for complex industrial applications, offering greater accuracy and ease of installation.

Can float level probes be used in hazardous areas?

Float level sensors can be used in potentially explosive atmospheres, provided they are properly designed and certified for such an application. For example, float transmitters from the JUMO NESOS series are available in variants that meet the requirements of explosion protection, including intrinsically safe (Ex i) and flameproof (Ex d) versions. Such solutions allow the float sensors to be used safely in environments where flammable gases, vapours or dust are present. Thanks to special designs and safety features, these sensors can operate safely in harsh environments without causing an ignition risk.

Tank level measurement with pressure transmitters

Pressure transducers are a reliable tool for measuring the level of liquids in tanks, working on the principle of measuring hydrostatic pressure. In practice, this means that a transducer placed at the bottom of the tank or in the lower part of the tank measures the total pressure exerted by the liquid, allowing the level to be accurately determined. This method is ideal for tanks of various sizes and types, including closed tanks, where the transducer compensates for the additional pressure. Their key advantage is their high accuracy and resistance to harsh conditions such as the presence of vapours or chemicals. The versatility of the pressure transmitters makes them widely applicable to a variety of industries, from chemicals to waste water processing, providing precise and stable liquid level measurement.

About the author

My name is Ewelina Szmit and I have been working in the field of content marketing for several years, combining my professional skills with my passion for writing. I believe that even the most technical topics can be presented in a way that is interesting and accessible to everyone. Outside of work, I develop my creativity by making newspaper collages. I like to spend my free time most actively, walking my dog or running.

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