Level Sensors

How Hygienic Level Sensors Optimize Your Processes

Achieving optimal production processes and maximizing resource efficiency requires precise and continuous monitoring of level, volume, or mass in storage and process tanks. Anderson-Negele offers advanced level measurement technologies tailored for various tanks, media, and applications. Whether you need hydrostatic, potentiometric, weight measurement, or differential pressure solutions, we have the right sensor for every need.

Hydrostatic Instrumentation from Anderson-Negele

Anderson-Negele provides a comprehensive range of level sensors designed to meet the stringent demands of hygienic applications in industries such as dairy, brewing, food, and beverage. For the life sciences sector, we offer specialized pharmaceutical versions that cater to even higher requirements.

Our product lineup includes everything from the cost-effective P42 with IO-Link to the high-performance L3 model. The L3 features intelligent electronics with enhanced temperature compensation via an integrated temperature measuring cell, density compensation for various media, and integrated tank linearization for diverse or custom vessel shapes. This ensures highly accurate outputs in gallons, pounds, PSI, and other units, outperforming comparable devices. For outdoor or challenging environments, the LAR sensor prevents climate-induced drift with a hermetically sealed measuring system, ensuring reliable results. Additionally, our D3 Differential Pressure and Level Control sensor, based on the L3’s advanced technology, offers a solution with dual pressure detectors and integrated electronics for precise differential pressure output.

Potentiometric Level Sensors from Anderson-Negele

The NSL measuring system is the foundation of Anderson-Negele’s extensive range of potentiometric level sensors, designed to meet diverse application needs across various industries. This versatile technology allows for a wide array of configurations:

• NSL-F: A level sensor with integrated electronics and a programming display for easy setup and monitoring.
• NSL-FR: A remote version with separate electronics, perfect for installations in hard-to-reach areas or where strong vibrations occur during the process.
• NSL-F-01: A curved version designed for installation in the side wall of tanks, offering flexibility in challenging tank geometries.
• NSL-F-02: A dual probe model ideal for non-metallic vessels, ensuring accurate level measurement in a broader range of materials.
• NSL-M: A compact, mini variant without a display, designed for direct data output to the PLC, making it suitable for streamlined installations.
• IO-Link with Flex Hybrid Technology: Available for all NSL-F variants, providing advanced connectivity and integration options for modern industrial setups.

Weighing Systems from Anderson-Negele

In many industrial applications, weighing systems offer a more practical and accurate solution for level detection compared to other measuring techniques. Anderson-Negele provides precise, robust, and efficient weighing solutions with a proven track record in the field.

Accurate inventory control in process vessels, storage tanks, and silos is often challenging. Traditional methods like hydrostatic sensors, potentiometric probes, or radar can sometimes fall short in terms of precision, speed, flexibility, or cost-effectiveness. Anderson-Negele addresses these challenges with advanced weighing technology, offering the following systems:

• Load Disc Weighing Modules: Ideal for precise measurement in challenging environments, providing reliable performance where other methods may fail.
• Load Stand Weighing Systems: Designed for robust applications, these systems ensure accurate level detection in large tanks and silos.
• Bolt-On Load Cells: Offering a cost-effective and practical solution for retrofitting existing vessels, these load cells provide dependable accuracy without the need for extensive modifications.

Choosing the Right Technology for Your Application

Selecting the best technology for level measurement depends on various factors that influence performance and accuracy:

• Container Characteristics: Consider the type, size, shape, and material of the container to determine the most suitable measurement method.
• Media Type: Differentiate between liquid media and solid particles like granules or powders, as each requires specific measurement technologies.
• Material Properties: Assess whether the media is liquid, pasty, adhesive, foaming, or conductive/non-conductive to ensure accurate readings.
• Measurement Accuracy: Identify the level of precision required for your application to select the most appropriate sensor.
• Media Conditions: Factor in the media’s temperature, density, and their potential dynamic variations during the process.
• Consistency of Media: Determine whether the media changes frequently or remains consistent, impacting sensor choice.
• Installation Location: Consider whether the sensor will be installed indoors or outdoors, and how climatic conditions may affect performance.
• Pressure Conditions: Evaluate whether the environment is at atmospheric pressure or involves a pressurized tank, as this can influence the technology selection.

What is Hydrostatic Level Measurement?

Hydrostatic level measurement relies on the pressure exerted by a liquid within a vessel, acting vertically on all walls. As the liquid level rises, so does the pressure. A sensor (transmitter) positioned at the bottom or lower edge of the vessel measures these pressure variations and transmits the data to the PLC (Programmable Logic Controller). Depending on the installation requirements, the sensor diaphragm can be mounted at the vessel’s bottom or laterally at the bottom edge.

Pressure transmitters use a piezoelectric signal converter to convert the mechanical pressure detected by the sensor diaphragm into a proportional voltage signal. This signal is then output as a 4…20 mA standard signal or another protocol based on the customer’s needs.

Modern systems, like the Anderson-Negele L3, enhance hydrostatic measurement by directly converting pressure values into volume or mass in the sensor electronics. This advanced capability requires input on factors such as container shape, medium, and process temperature to calculate specific density accurately. The L3’s integrated temperature compensation ensures higher accuracy across the entire process temperature range, enabling precise readings in gallons, pounds, PSI, or other units, even under dynamic temperature conditions.

For open systems (vessels with atmospheric pressure), a single pressure sensor at the bottom of the vessel suffices, as external pressure remains constant. In closed systems (pressurized vessels), varying pressures can affect the measurement. In these cases, two sensors are used: one to measure the process pressure at the bottom and another to measure the head pressure at the top. The differential pressure between these two readings is calculated in the PLC or an evaluation unit, providing an accurate fill level.

How Does a Hydrostatic Pressure Transmitter Work?

A hydrostatic pressure transmitter operates by measuring the pressure exerted by the liquid within a vessel. The pressure sensor is installed in the vessel wall, with its diaphragm positioned perpendicular to the contents. As the process or level pressure increases, it deforms the diaphragm. This deformation is transmitted via a capillary fluid to a measuring cell equipped with a piezoelectric signal converter, which transforms the process pressure into a corresponding voltage signal.

The sensor’s internal electronics then convert this voltage into the industry-standard output, such as analog 4…20 mA or HART 7.0, depending on the customer’s requirements. This allows the hydrostatic pressure to be accurately output as an electrical signal to the PLC, enabling precise level monitoring and control.

What’s the Difference Between Relative and Absolute Pressure Gauges?

Relative pressure gauges measure the process pressure in relation to atmospheric pressure. In these sensors, the back of the diaphragm is vented, allowing the transducer to account for changes in atmospheric pressure. On the other hand, absolute pressure gauges measure pressure relative to a vacuum. During manufacturing, a vacuum is sealed between the diaphragm and the sensor’s base body, providing a stable reference point.

Because atmospheric pressure can fluctuate due to meteorological changes, absolute pressure gauges generally offer higher measurement accuracy, making them ideal for applications where precision is critical.

What is Temperature Compensation for Pressure Transmitters?

Temperature compensation is a critical feature for pressure transmitters, especially in industries like food and beverage where precision under fluctuating temperature conditions is essential. The Anderson-Negele L3 sensor is engineered for high accuracy in such environments, using a piezoelectric signal converter combined with an integrated temperature sensor. This setup measures both the pressure and temperature of the internal capillary fluid, ensuring accurate pressure readings.

The sensor’s electronics convert the mV signal from the converter and the resistance from the temperature sensor into an adjusted pressure value. This temperature compensation corrects for errors that can occur due to temperature effects or drift. For example, as temperatures change, the specific density of a medium also changes, which can lead to inaccurate level measurements if not properly compensated.

Conventional sensors may experience a temperature drift of up to 0.4% per 10°C, leading to significant inaccuracies at higher temperatures. At 110°C, this drift can exceed 2.5%. In contrast, the L3 sensor boasts a remarkably low temperature drift of just 0.03% per 10°C, resulting in a drift of less than 0.4% even at 110°C—six times lower than conventional sensors. This superior temperature compensation ensures highly accurate measurements, even in dynamic temperature environments.

What is Potentiometric Level Measurement?

Potentiometric level measurement relies on changes in the voltage ratio between the sensor’s electrode rod, which is immersed in the liquid, and the metallic wall of the filled tank. This voltage ratio changes proportionally with the height of the liquid in the tank, allowing for precise level detection. The measured values are then processed and output by the sensor’s electronics.

This measurement technique is specifically suited for liquids with electrical conductivity, typically at levels greater than 50μS/cm, as required by Anderson-Negele sensors. Potentiometric level measurement is versatile, making it ideal for use in both closed and open process tanks, feed tanks, storage tanks, and even pressurized tanks. For non-metallic tanks, a sensor variant with a reference rod is available to ensure accurate readings.

How Does a Potentiometric Level Sensor Work?

A potentiometric level sensor consists of an electronic unit and a measuring rod that extends into the liquid within the tank. The sensor can be installed in various positions, including from above, below, diagonally, or even in the side wall of a tank using a version with a bent measuring rod. The length of the measuring rod can be customized to fit the tank in 10 mm increments, up to a maximum of 3 meters, with intermediate sizes available upon request.

Once installed, the sensor generates an electric flow field within the liquid, influenced by the medium’s electrical conductivity and capacitive properties. This creates a voltage ratio that is directly proportional to the immersed portion of the rod. Since the sensor focuses solely on the voltage ratio, the medium’s properties, such as electrical conductivity, do not affect the measurement accuracy.

Anderson-Negele’s NSL sensors take accuracy a step further by utilizing a second, patent-pending measurement method. This method evaluates the electrical resonance properties to determine the exact immersion state of the electrode rod. It also effectively detects and compensates for foam, preventing erroneous readings caused by foam or adhesion. This ensures reliable and precise level measurement, even in challenging conditions.

Products and Applications Suitable for Potentiometric Level Measurement

Potentiometric level measurement is ideal for a wide range of media and applications, thanks to its insensitivity to foam and buildup, exceptional measuring accuracy, and extremely short response times. This technology is particularly well-suited for dairies, breweries, milk and beverage processing, as well as the food and life science industries. The primary requirements are the electrical conductivity of the medium and a container height of up to 3 meters.

The flexible and modular NSL sensor system ensures reliable and precise measurements, even in challenging conditions and demanding applications, including:

• Various Fluids: Suitable for products, CIP media, water, and more.
• Specific Applications: Ideal for use in milk heaters, bottling plants, ice cream production, separators, brewing and lauter tanks, and horizontal tanks.
• Foaming Media: Handles strongly or variably foaming media such as beer, juices, and dairy products.
• Pasty Media: Effective with pasty or adhesive media like creams, ice cream, ketchup, and sauces.
• Pressurized Tanks: Compatible with pressurized environments.
• Rapid Level Changes: Performs well in scenarios with fast level changes, such as during filling.
• Non-Metallic Tanks: Works efficiently in non-metallic tanks.
• Changing Media: Automatically adapts to different media within the same tank.
• Complex Tank Shapes: Suitable for tanks with limited installation possibilities.
• Harsh Environments: Withstands high mechanical or chemical stress, including exposure to cleaning agents.

Signals and Parameters for Potentiometric Measurement

The NSL sensor system’s high-precision measurement process, combined with intelligent electronics, offers various signals and adjustable parameters:

Output Signals:

• Level Height: 4…20 mA or digital IO-Link signal with <1% measuring accuracy.
• Dry Running Warning: Prevents potential damage due to low levels.
• Failure Warning: Alerts in case of system malfunctions.
• Underflow/Overflow Limitations: Signals and errors related to underflow or overflow conditions.
• Signal Simulation: 3.95…20.05 mA for testing and calibration purposes.

Adjustable Parameters:

• Fill Level Zero Point/Offset: Fine-tuning the sensor’s starting point.
• Level Slope/Gain: Adjusting the sensitivity of the measurement.
• Attenuation/Filter: Smoothing out signal noise for more stable readings.
• Physical Unit: Setting the desired unit of measurement.

What is Inventory Measurement by Weighing Systems?

In many applications, weighing systems offer a more practical and precise solution for level detection compared to other measurement techniques. Anderson-Negele provides robust, efficient, and field-proven weighing systems that excel in scenarios where traditional methods fall short.

Accurate fill quantity determination in process vessels, storage tanks, and silos is often challenging. Classical measurement systems like hydrostatic sensors, potentiometric probes, or radar may not be precise, fast, or flexible enough for certain environments. They can also be impractical due to technical limitations or cost constraints.

Challenges Addressed by Weighing Systems:

• Process Vessels with Agitators: In vessels with agitators, sensors that protrude into the medium are not feasible. The dynamic forces and motion of substances create challenges for traditional sensors. Weighing systems allow for precise measurement and control of dosed and dynamically added ingredients, even during ongoing processes. These systems are also effective in closed stirring systems with negative or positive pressure.
• Interchangeable Movable Containers: For applications like yogurt mixing, where containers are frequently moved or replaced, installing individual level sensors is impractical and costly. Weighing systems provide a flexible solution without the need for permanent sensor installations.
• Horizontally Stored Tanks: In horizontally stored tanks, even small changes in fill level can cause significant volume shifts. The inherent movement (sloshing) of liquids further complicates measurement by traditional level sensors. Load cells offer more reliable results by accurately measuring weight, regardless of the liquid’s movement.
• Tanks for Dry Bulk Materials: In tanks or silos storing dry bulk materials, uneven mass distribution (such as piles, funnels, or ratholes) can lead to inaccurate surface measurements. Due to their size and height, classic continuous level probes are often not suitable. Weighing systems provide an accurate solution by converting the entire container into a precision scale.

The Solution: Turn Your Container into a Precision Scale

By implementing weighing systems, you can transform your container into a highly accurate scale, ensuring precise inventory measurement and control. For more details, visit the Kistler-Morse Website and explore their Weighing Systems product section.