Level Control for Industrial Applications

Level control describes the technical detection and monitoring of liquid levels in containers, tanks or canisters and their use for controlling downstream processes. Typical applications are found in dosing technology, in pump systems and in industrial plants in which liquids must be conveyed or dosed safely, reproducibly and as required.

The goal of level control is to reliably adapt the operation of pumps and dosing systems to the actual fill level. This includes, among other things, timely shutdown in the event of an empty condition, preventing overfilling, and providing measured values for higher-level control systems. Correctly designed level control helps to avoid plant downtime, protect components from damage and keep process sequences stable.

In industrial practice, the term level control is often used together with level switching. While switching usually refers to the direct switching on or off of pumps or alarms, control can also provide continuous measured values that are used for finely tuned dosing of liquids. Which design is sensible depends on the respective process, the medium and the requirements for accuracy and safety.

For applications in dosing technology, for example when extracting liquids from containers via suction lances, level control plays a central role. It ensures that dosing pumps are always sufficiently supplied and are automatically switched off when the container is empty. At the same time, fill levels can be monitored in order to be able to respond to refilling requirements in good time.

What Level Control and Level Switching Achieve

Level control and level switching perform the task of detecting liquid levels in technical systems and deriving targeted switching or control functions from them. They form the basis for the safe and controlled operation of pumps, dosing systems and downstream processes. Depending on the application, the focus is either on individual switching points or on a continuous measurement range.

Typical Objectives in Systems and Processes

In many industrial applications, the goal is not to know the exact fill level at every moment, but to reliably detect defined states. Level switching is therefore often used to avoid critical operating conditions and to stabilize system operation. This includes, in particular, protecting pumps from dry running and preventing overfilling of containers or collecting trays.

In addition, level control supports a consistent and predictable process sequence. In dosing technology, it enables liquids to be extracted as required and dosing pumps to be operated only when sufficient medium is available. Early empty signals help to initiate refilling processes in good time and avoid unplanned downtime.

Limit Detection Versus Continuous Measurement

In principle, two approaches can be distinguished. Limit detection solutions detect whether a defined fill level has been reached or fallen below. They provide a clear switching signal and are particularly suitable for applications such as on and off operations, alarm messages or simple two point controls.

In contrast, continuous measurement systems provide an ongoing measured value across the entire fill level range. This value can be transmitted to a control or regulation system and enables finer adjustment of conveying capacity or dosing quantity. Such solutions are used when the dosing of liquids is to be closely linked to the current fill level or when permanent monitoring is required.

In practice, both approaches are often combined. A continuous measurement can guide the process, while an additional limit level serves as an independent safety layer. This separation of control and protection function increases operational safety without unnecessarily complicating the system design.

Technologies for Level Control at a Glance

Depending on the application, different sensor technologies are available for level control. They differ primarily in the measuring principle, the information content of the signal and their operating conditions. Selection is based on the medium, container geometry, process requirements and the desired integration into pump or system control. 

Float Switches as a Limit Level Solution

Float switches detect a liquid level via a mechanically moving float that follows a defined level. When the switching point is reached, a contact inside is actuated, generating an electrical signal. This technology is used when clear limit levels need to be monitored, for example for empty signals or overfill protection.

Typical characteristics and advantages of float switches are:

• clear switching signals for on and off operations
• simple integration into existing pump control systems
• suitability for many liquids due to different materials
• possibility to implement multiple switching points in one system
• manageable installation effort for clearly defined fill levels

Float switches are often used where robustness and clear status signals are more important than continuous measurement.

Transmitters for Continuous Level Signals

Transmitters measure the fill level continuously over the entire measuring range and convert it into an electrical output signal. This signal can be passed on to a higher level control system and processed further there, for example to regulate pump performance or dosing quantities.

Characteristic features of this technology are: 

• continuous information about the current fill level
• connection to control systems via standardized signals
• possibility of visualization and trend monitoring
• support for precise dosing of liquids
• use in applications with variable or dynamic fill levels

Transmitters are preferably used when processes need to be actively controlled or monitored and not only limit states are relevant.

Conductive Rod Electrodes Without Moving Parts

Conductive rod electrodes operate according to the conductivity principle. As soon as the medium touches an electrode, the electrical resistance changes, generating a switching signal. The prerequisite is that the liquid is electrically conductive. Since there are no moving parts, this technology is suitable for applications with high requirements for low maintenance.

Key properties of conductive rod electrodes are: 

• detection of limit levels without mechanical movement
• possibility of multipoint detection with several electrodes
• suitability for applications with conductive liquids
• low wear due to the absence of moving components
• use as overfill protection, dry run protection or two point control

Conductive rod electrodes are often used where simple limit level information is required and the media conditions allow the measuring principle.

Dosing Technology as an Application with High Practical Relevance

In dosing technology, liquids are extracted in a controlled manner from storage containers and supplied to defined processes. The dosing of liquids is often carried out via pumps that draw from canisters, drums or tanks. For this process to function reliably, a stable supply of medium is required. This is precisely the interface where level control performs a central function.

Without suitable level switching, there is a risk that dosing pumps will continue to run when the container is empty or nearly empty. This can lead to malfunctions in the process and increase wear on the pump. At the same time, without level monitoring there is no reliable basis for planning refilling operations and designing dosing processes in a reproducible manner. An integrated level control system therefore supports both component protection and process reliability.

Suction Lance with Integrated Level Control

The suction lance combines medium extraction and level monitoring directly inside the container. It is inserted into the storage container and supplies the medium to the dosing pump. Integrated sensors detect the current fill level or defined limit levels, for example for empty detection.

Typical features of suction lances with level control are:

• combination of medium extraction and level monitoring in a single component
• automatic shutdown of the dosing pump when empty
• early notification of low fill level for process planning
• compact design for canisters and smaller containers
• versions for different media and container sizes

Through this integration, additional installations in the container can be avoided and installation effort reduced. Suction lances are therefore frequently used in compact dosing systems.

Dosing Liquids with Stable Supply and Shutdown

When dosing liquids, not only dosing accuracy is decisive, but also the continuous availability of the medium. Level switching ensures that liquids are dosed only when a sufficient fill level is present. At the same time, it enables a defined shutdown before air is drawn in or the dosing process is interrupted.

Especially in applications with frequent media changes or limited space, the combination of a suction lance and integrated level control has become established as a practical solution.

Design, Selection and Technical Coordination

The reliable function of a level control system depends largely on proper design. As early as the planning phase, the operating conditions should be clearly defined so that the sensor technology and design match the medium, the system and the desired functional scope. A structured consideration of the most important parameters facilitates selection and reduces later adjustments during operation.

In practice, the following sequence has proven effective for technical coordination: 

1. Medium and chemical properties
   Decisive factors are conductivity, density and possible chemical interactions with the sensor material. These factors determine whether, for example, float switches, conductive rod electrodes or transmitters are suitable.
2. Temperature and environmental conditions
   The permissible temperature range of the medium and the environment influences material selection and electrical design. Protection class and installation situation are also relevant here.
3. Container geometry and installation situation
   Height, diameter, openings and installation position of the container define which design is appropriate. In canisters or smaller containers, compact solutions such as suction lances are often used.
4. Switching points and signal type
   It must be clarified whether a simple empty signal is sufficient or whether multiple switching points are required. Alternatively, a continuous signal may be necessary, for example to control the dosing of liquids.
5. Materials and mechanical design
   Depending on the medium and the application, different plastics or metals are used. The selection has a direct impact on resistance and service life.

In addition to selecting a single technology, combining different variants is also a common approach. In many applications, continuous level measurement is used to guide processes or control dosing quantities. In addition, a separate limit level sensor can be used that independently performs a shutdown or alarm function regardless of the measurement signal. This combination makes it possible to support ongoing operation as well as defined protective functions without unnecessarily complicating the system architecture.

Level control and level switching are used wherever liquids need to be safely monitored, conveyed or dosed.

Typical fields of application beyond dosing technology include, among others: 

• Chemical processes and cleaning systems
  Control of aggressive or sensitive media, empty detection and overfill protection.
• Water and wastewater technology
  Level monitoring in containers, collecting basins and technical installations.
• Machinery and plant engineering
  Integration of level switching into pumps, units and compact systems.
• Process related supply systems
  Ensuring media availability for downstream process steps.

By selecting suitable sensor technology, these applications can be implemented both with simple limit level solutions and with continuous measurement. Level control therefore supports reliable dosing of liquids and robust pump control across a wide range of industries.

Guidance and Service at Reed Electronics AG

Reed supports customers in selecting and designing suitable solutions for level control and level switching. This includes technical coordination based on the medium, container, installation situation and desired signal type, as well as clarification of whether limit level solutions, continuous transmitters or combined variants are appropriate. Reed also supports integration into existing pump and control concepts, including applications in dosing technology such as suction lances for safe media extraction. The goal is a technically appropriate, transparently designed solution that integrates reliably into the respective process.

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