[Translate to Englisch:] CAPTRON Kompaktsonde

April 6th, 2023 | 11 minutes read | CAPTRON editorial office
(This is the revised version of a post from August 5th, 2020)

Which is the best level sensing technology to measure my medium?

Economic decisions in today's industrial automation depend on reliable measurement data. For plant operators, process monitoring and control of machines is therefore an important tool. This is especially true in the area of level measurement. But which level sensing technology is best suited for my application and the medium to be measured?

Generally speaking, the choice of level sensing technology depends on which liquid or material is involved, whether it is chemically aggressive, and whether a single measurement or continuous measurement is required. The vessel size and the operating environment, such as high temperatures, pressure and dust, also play a role.

The following overview explains different technologies for level sensing of liquids, bulk solids, pastes, adhesives and chemically aggressive materials to facilitate your choice of the right method.

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Overview of the most important technologies for level measurement

[Translate to Englisch:] symbol Time of Flight

ToF („Time of Flight") laser

Level measurement by the Time-of-Flight ("ToF") method measures the distance of the medium from the sensor by the time it takes the light to travel from the sensor to the medium and back. A level change leads to a change in the runtime of the light and thus to the measurement and display of the changed level.

The advantage of level measurement by ToF with laser is the very fast and accurate non-contact measurement even in special environments with high pressure and explosion hazard or in dust and fog.

ToF measurement by laser is particularly suitable for bulk solids measurements, since the measurement is performed without contact with the medium and is therefore independent of the medium's characteristics. In addition, the measurement method with ToF laser is cost-effective.

[Translate to Englisch:] symbol optische Reflektionsmessung


Optical reflection measurement exploits the refraction of light on the medium to detect the level of liquids. Refraction is the phenomenon where light rays change direction as they pass from one material to another. This occurs because the speed of light is different in different materials. Optical reflectance sensors consist of a light emitter and a photodetector that measures the reflected light. When a liquid is present, the light is refracted and thus only a portion of the light is reflected, resulting in a corresponding change in the electrical signal.

This is an invasive method that requires contact with the liquid, but is an inexpensive and practical solution for level measurement and leak detection at high temperatures and pressures. Such sensors can only detect a certain level and are susceptible to contamination.

[Translate to Englisch:] symbol der kapazitive Füllstandsmessung


Capacitive level measurement is a method for measuring the level of liquids or solids in a container, whereby the electrical capacitance is measured between a measuring rod (electrode) and the conductive container wall. The higher the level of the medium, the greater the measured capacitance of the capacitor formed. In the case of a non-conductive tank, the capacitance changes can also be measured between two measuring rods or a measuring rod and a cladding tube.

In addition to the level, the capacitive measurement is also influenced by the dielectric constant of the medium (DK value). Therefore, a calibration to the respective medium is required, which can be done either already at the factory, by an adjustment procedure or by a DK value input to the measuring system. Capacitive level measurement is a very precise and reliable method. It is often used in industry, especially in applications where accurate level measurement and control is required, such as in the chemical industry, food industry, pharmaceutical industry and special machine construction.

[Translate to Englisch:] Füllstandsmessung durch Ultraschall


These level sensors emit ultrasound so that the distance between the sensor and the liquid can be determined based on the travel time of the reflected sound wave. This is an accurate, non-contact method that is not affected by the type of material being measured. However, level measurement by ultrasonics is complex and expensive. In addition, problems occur with foaming liquids and complex container shapes.

Moreover, the method does not work with vacuumed containers, since sound cannot propagate in the airless space. As with all measurement methods based on the ToF method, there is a dead zone in the upper area of the container, so that the container cannot be filled completely.

[Translate to Englisch:] Füllstandsmessung mittels Radar


Level measurement by radar is similar to ultrasonic measurement. However, radar sensors transmit electromagnetic microwaves in the frequency range of up to 120 GHz, instead of ultrasound. The level of the measured product is determined by the duration between the transmission of the microwave signal and its echo (ToF method).

Radar sensors are accurate even at large measurement distances and do not require calibration. But they are expensive. With this measuring principle, similar problems (dead band) occur as with ultrasonic sensors. However, radar sensors also work in a vacuum. Normally radar sensors are used for measuring larger distances (1 m -50 m), for example in grain silos.

[Translate to Englisch:] Füllstandsmessung mittels Vibrationssensoren


This method is particularly suitable for liquids as well as for powdery and fine-grained solids in the mining, chemical and food industries. Vibration sensors have a fork-shaped probe that vibrates at its natural frequency. A change in frequency indicates a change in level. This method is inexpensive and compact, but requires contact with the material.

Since you can only measure a certain level per sensor, measurement by vibration usually only measures discrete levels, such as a certain limit level or 40%, 60%, and 80%. Vibration sensors are also not very repeatable.

[Translate to Englisch:] Füllstandsmessung durch Prüfung der Leitfähigkeit


Between the probes used in this measurement technique, a voltage is applied between two electrodes to measure the conductivity or electrical resistance of the material. As long as the probe is covered with liquid, the circuit remains closed and current flows. As soon as the probe is no longer covered, the circuit is broken and can thus indicate a low or high level (discrete measurement).

Such sensors are inexpensive but in contact with the medium and can only be used with consistently conductive liquids, such as drinking water. In addition, the probe may corrode over time.

[Translate to Englisch:] Füllstandsmessung mittels Schwimmer


Another sensor for easy detection of a high or low level is the float switch. This rises or falls as the level in the vessel or tank increases or decreases. This mechanical sensing principle requires no power supply and is inexpensive.

However, compared to other sensors, float switches are relatively large and less reliable because they can become dirty and stuck in the tank.

[Translate to Englisch:] Füllstandsmessung mittels Last


Load sensors measure the weight of a container to determine the level. In this process, the load sensors are attached to the support of the container and measure the weight exerted by the container. Any change in weight corresponds to a change in level.

Load sensors are suitable for both liquid and solid media, as long as the material has a uniform density. The supply lines of the tank, which falsify the weight measurement, are problematic.

The differences in the measurement technologies at a glance

[Translate to Englisch:] CAPTRON kapazitive Füllstandsmessung

Capacitive level measurement with CAPTRON

As a specialist in level measurement, CAPTRON uses capacitive as well as ToF laser technology for level measurement.

As the figure on the right shows, the operating principle of capacitive level measurement is based on the change in capacitance of a capacitor. In this example, the probe rod and the vessel wall form the two electrodes, while the medium acts as the dielectric. The change in level causes a change in capacitance. An empty vessel has a low capacitance, while a filled vessel has a high capacitance.

Selection Criteria for Capacitive Probes

The selection criteria depend on numerous factors – 1-rod probes are used for metal vessels, while double-rod probes or a 1-rod probe with a cladding tube are used for plastic vessels. The environmental conditions, such as temperatures above 100 °C, and the required protection class, e.g. IP67, determine whether an external amplifier is required or what type of instrument connection is needed.

Special designs according to customer specifications

In every industry, very different requirements are placed on products and materials. That is why CAPTRON offers a range of probe systems that can be combined and customized. Depending on the application and type of vessel, the company's systems can be used to configure probes that meet very specific customer requirements - right down to probe lengths that are accurate to the millimeter. Custom designs are an important consideration, especially for different vessel sizes. CAPTRON meets these requirements and offers probes or even dual probes in the desired length and with sensors that measure many different liquids and powders. Due to the material options, corrosion does not occur. Special designs are developed according to customer specifications, especially the rod length can be determined to the centimeter and delivered within two weeks. CAPTRON's level sensors are extremely reliable and very accurate. There are systems that have been in operation for over 20 years. CAPTRON also takes care of the precise calibration of probes with regard to the vessel geometry, the measured material (DK value) and other influencing factors, such as temperature or the movement of an agitator, among others. Compact probes with integrated electronics in the housing or probes with external amplifiers are available. The external amplifier is connected via a shielded, temperature-resistant Teflon cable to the rod probe. Due to the spatial separation of the rod probe and the amplifier, these probes are suitable for temperatures of up to 230 °C.


[Translate to Englisch:] CAPTRON kapazitive Füllstandsmesstechnik
Capacitive level measurement
CAPselect - free configuration of your device

With the CAPselect system for level sensors, you are able to freely configure the probe of your choice depending on the application, container type and sensor properties. CAPTRON produces these with millimetre accuracy to ensure full flexibility.