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Analogue level and temperature measurement reed chain

In today's high-tech world, level and temperature measurement in industrial plants, tanks, and containers is becoming increasingly important. Level and temperature measurement is a fundamental process in industry and significantly influences the efficiency and safety of operations. Analog level measurement using a Reed chain in combination with a temperature sensor such as the PT100/PT1000 or bimetallic temperature switch has proven to be a true leader in this field. It allows for continuous and accurate monitoring of liquid levels and additionally measures or monitors temperature.

Operating Principle

The operating principle of an analog level sensor with a Reed chain in combination with a float is based on utilizing the upward and downward movement of a float in the liquid level. The level sensor consists of a Reed chain and a float. The Reed chain consists of several individual Reed switches attached at regular intervals to a flexible metal strip. Each Reed switch consists of two ferromagnetic contacts separated by a glass housing. In contrast, the float is a buoyant body that rests on the surface of the liquid and rises or falls in response to the fill level. The float is equipped with a magnet, while the Reed chain is positioned vertically inside the container. As the fill level changes and the float ascends or descends, the magnet moves along the Reed chain. The individual Reed switches in the Reed chain respond to the magnet's magnetic field. When the magnet approaches a Reed switch, the contacts of the Reed switch close, generating an electrical signal. This signal is then captured by a measuring device or evaluation unit and converted into a measurable value. In addition to this functionality, temperature measurement is integrated to monitor the temperature of the liquid in the container.

Analog temperature measurement is achieved using highly accurate temperature sensors such as PT100 or PT1000. These sensors rely on the principle of a metal's electrical resistance changing with temperature. A PT100 sensor consists of a platinum resistor that changes its resistance value as the temperature increases. Similarly, a PT1000 sensor operates, but its resistance is 1000 times greater than that of a PT100. PT sensors are capable of providing very precise and accurate resistance values directly related to the temperature of the liquid or medium in contact. These analog resistance values are then converted into temperature values and displayed through an appropriate measuring device or evaluation circuit. Temperature values can also be transmitted to control and regulation systems to monitor the temperature in the facility and potentially control and regulate the process.

The bimetallic switch consists of two metal strips with different coefficients of thermal expansion connected to each other. When the switch is exposed to a certain temperature, the metal strips deform due to their different rates of expansion. This deformation leads to a mechanical movement of the switch. The temperature switch uses the bimetallic switch as a sensor to monitor temperature. When the temperature reaches or exceeds the preset threshold, the deformation of the bimetallic switch causes a movement that either opens or closes the electrical contact. When the switch is open, the circuit is interrupted, and no current flows. This can serve, for example, as a protective device to prevent overheating. When the switch is closed, the circuit is completed, and current can flow.


  • Precise Monitoring: The combination of level and temperature measurement allows for precise monitoring of liquids and process parameters, enabling early detection of deviations and appropriate corrective actions.
  • Efficient Process Control: Continuous measurement of level and temperature enables efficient process control. Facilities can automatically respond to changing conditions to ensure optimal performance and quality.
  • Enhanced Safety: Accurate tracking of liquid level and temperature contributes to process safety. Potential hazards such as overfilling or overheating can be detected and avoided in a timely manner.
  • Reduced Downtime: Timely detection of level or temperature variations allows for proactive maintenance or servicing of equipment, minimizing unforeseen downtime.
  • Efficient Resource Utilization: Accurate measurement of level and temperature enables more efficient use of resources, including liquids, energy, and materials, leading to cost savings.
  • Improved Product Quality: Continuous monitoring of level and temperature ensures consistent processing of materials and ingredients, enhancing product quality.
  • Flexibility and Adaptability: Sensors capable of measuring both level and temperature are versatile and can be adapted to various industries and applications to meet specific requirements.
  • Easy Integration: Modern sensors are often equipped with digital interfaces, facilitating easy integration into existing control and automation systems.
  • Long-term Cost Savings: By avoiding overfilling, overheating, or unexpected failures, long-term cost savings can be achieved by avoiding costly repairs or production interruptions.
  • Environmental Friendliness: Efficient process control often leads to reduced environmental impact as the use of raw materials and energy is optimized.

Applications and Industries

Chemical and Petrochemical Industry
Monitoring tanks and containers containing chemicals or oil products is critical for tracking inventory and safely handling substances.

Food and Beverage Industry
Precise monitoring of liquid levels in production equipment, along with temperature monitoring, ensures product quality and safety.

Heating and Cooling Systems
In boilers, air conditioning, and cooling systems, combined sensors enable efficient control of heating and cooling processes by monitoring both water level and temperature.

Environmental Protection Applications
In environmental protection systems, these sensors are used to monitor liquid level and temperature in waste and wastewater tanks to ensure compliance with environmental regulations.

Pharmaceutical Industry
Accurate monitoring of level and temperature in reactors and fermenters is required to control and optimize production processes.

Power Generation
In power plants and turbines, combined sensors are used to monitor water level and temperature in cooling systems and heat exchangers to improve energy generation efficiency.

Lubrication Systems
In machinery and equipment lubrication systems, these sensors monitor the level and temperature of lubricating oil or grease to ensure the smooth operation of moving parts and prevent damage.

Steam Generators and Boiler Systems
In steam generators and boiler systems, combined sensors are used to monitor water level and temperature to ensure safe and efficient steam generation.

Textile Machinery
In the textile industry, these sensors monitor the level and temperature of chemicals or dyes in textile machines to ensure uniform and precise processing.

Printing Machines
In printing machines, these sensors monitor the level and temperature of printing inks or solvents to ensure smooth print quality.


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D-72535 Heroldstatt

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Industry sectors

  • Hydraulic units
  • Chemical industry
  • Dosing filling equipment
  • Electroplating
  • Food industry
  • Machinery and equipment construction
  • Medical
  • Overview industries

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