Level-Transmitter Sensors for Continuous Fill-Level Monitoring
What are Reed Level-Transmitter Sensors?
Level transmitter sensors are the silent safeguard for precise processes. They continuously detect the liquid level and convert it into an electronic signal – either as resistance, voltage or a standardized 4 to 20 mA current. This enables reliable continuous monitoring of tank contents from 0 to 100 percent, automation or integration into control systems.
Reed Electronics AG offers customized solutions based on the proven reed chain measurement principle, ranging from compact miniature sensors for tight installation spaces to robust explosion-proof versions for demanding industrial environments.
Product overview
Operating principle of the reed chain in the level transmitter sensor
Reed level transmitters are based on a mechanically simple yet technically refined principle. The liquid level is detected by a float with a built-in magnet that moves along a guide tube. Inside this tube is the so-called reed chain, a series circuit of sensitive contacts that are activated one after the other by the magnetic field. The function is comparable to a resistive potentiometer.
Reed chain measuring principle showed
The float rises and falls with the level of the medium. The magnet installed in the float actuates the Reed chain within the sliding tube. By placing the Reed contacts in a row inside the sliding tube, various grids and thus different fill-level measurement resolutions can be generated. In addition to a three-wire potentiometer circuit, 4–20 mA or 0–10 V are also available as an electrical output.
Magnetic float and contact chain
The only moving part of the system is the float itself. As the liquid level rises or falls, the float moves accordingly without friction or additional power supply. As soon as the float’s magnet reaches a reed contact inside the guide tube, the contact closes. This creates a quasi-continuous signal that corresponds to the current fill level.
The major advantage is that the measurement is independent of the medium’s electrical properties such as conductivity or dielectric constant, and it is also insensitive to pressure, temperature, foam or vibration. This principle has proven itself over decades and is considered extremely reliable, maintenance-free and wear-free.
Understanding measurement resolution and dead zones
The accuracy of the level transmitter sensor is defined by the spacing of the reed contacts – common step sizes are 5, 10 or 15 mm. The closer the contacts are placed, the finer the resolution of the fill level. We also offer custom applications with up to 1 mm resolution.
Electrical output signals – from resistance to 4–20 mA output
The signal generated by a level transmitter sensor must match the application, whether for simple analog displays or integration into a control system. The reed chain technology is especially flexible, allowing for different signal types without complex electronics or calibration.
Resistance output vs. 4–20 mA current output
In the simplest case, the changing fill level is output as a change in resistance – ideal for short cable lengths or basic evaluation circuits. For industrial use, however, active signals are preferred:
- 4–20 mA current signal – the industry standard. Highly resistant to interference, even over long distances, and compatible with almost all control systems. As a 4–20 mA current output or current transmitter, the level transmitter sensor is particularly popular where reliability matters.
- 0–10 V voltage output – a common alternative, especially for shorter cable runs or control systems without current interfaces.
Depending on the model, signal outputs can be flexibly configured – with an additional temperature sensor or switch points for full and empty notifications.
Compatibility with control systems, IIoT and milliampere transmitters
Choosing the appropriate output signal allows the level transmitter sensor to be easily integrated into existing systems, whether for basic visualization or fully automated processes. The widely used 4–20 mA interface, for example, makes it a typical milliampere transmitter for process control and Industry 4.0 applications.
Advantages of Reed sensors
Design variants and material diversity
Whether it’s tight installation spaces, aggressive media or hazardous zones, the requirements for level measurement are as diverse as the applications. Reed Electronics AG addresses this variety with a modular system – each level transmitter sensor is individually tailored to the specific use case, starting from batch size one.
Are you looking for the right sensor for your application? Contact us for a non-binding consultation.
Standard version
For classic industrial applications, the standard version of the level transmitter sensor offers a wide range of configuration options. Selectable lengths from 100 to 2000 mm, various float diameters (Ø 16 to 52 mm), mechanical connections and electrical output signals (resistance, 4–20 mA or 0–10 V) make the system flexible for use in mechanical engineering, chemical plants or process automation.
At the heart of it is the proven reed chain, enabling quasi-continuous level detection with grid spacings of 5, 10 or 15 mm.
Mini level transmitter sensor – compact, encapsulated and robust
This version was developed specifically for confined spaces and demanding environments, such as mobile equipment, waste containers, chemical plants or OEM modules. With its slim guide tube and float diameter starting at Ø 25 mm, it allows precise continuous level measurements.
Two sensor technologies, each tailored to different application requirements, are available:
Hall sensor chain:
- Meets automotive standards – especially shock- and vibration-resistant
- Low sensitivity deviation – high precision and wider steps possible
- Factory-calibrated to magnet sensitivity – reliable switching even with temperature fluctuations
- Cost advantage – semiconductors are significantly cheaper to produce than mechanical reed contacts in glass housings
Despite minimal installation space, the mini Hall version can be fully integrated into 4–20 mA systems. For resistance or voltage output, the following sensor is used:
Plastic-encapsulated reed switches:
- Specially developed for the mini level transmitter sensor series in a fully encapsulated design
- Shock- and vibration-resistant, corrosion-resistant and durable – the sensor is also used in tractors and agricultural machinery
- Classic Reed principle in a robust miniature format with resistance or voltage output signal
- Passive component, no external power supply required
Explosion protection, temperature options, food-grade finish
Reed Electronics also offers matching variants for other demanding applications:
- Explosion-proof version for use in hazardous atmospheres (e.g. ATEX zones)
- Temperature sensors (PT100 / PT1000) or thermal switches as additional functional units
- Surface finish (electropolished) for hygienically critical applications in the food and beverage industry
- Different connection types – cable, terminal box or connector – depending on installation environment and customer requirements
Manufacturing is available in robust stainless steel, chemically resistant PVDF, PP or cost-effective PVC – matched to the media specification.
Special materials can be evaluated upon request.
