Fill levels must be recognized in countless storage, buffer and holding tanks in the process industry, food industry, and even in wind power plants or other fields.
The level switches used are normally as different as the various media being monitored. With the CleverLevel LBFS/LFFS switch, Baumer has developed a true all-rounder that uses frequency sweep technology. This method capitalizes on the fact that every material, regardless of its consistency, has a dielectric constant specific to that medium. This makes the new level switch suitable for practically all media, including liquids, granulates and even electrostatic media. At the same time, it is unaffected by adhesive substances or foams that may lead to switching errors with other technologies. Furthermore, it can distinguish between different media. This makes the CleverLevel more than merely a replacement for the traditional vibrating fork used in level control. Configuration is possible using Teach-in. It is more convenient with Flex Programmer software, which enables visualization at the same time. The displayed information can be communicated to a higher-level controller if required and interpreted there in accordance with the operation phase.
Figure 1: Level control in a container.
Level detection is of great importance in the process industry. They monitor maximum and minimum values of material fill levels in tanks or as protection against overflow or dry operation. A number of limit switches are available, based on different technologies. The specific application determines the selection, because until now it was not possible to cover all applications with one level switch. Things are different now. A new level switch that uses frequency sweep technology now proves to be a practice-oriented all-rounder for almost every conceivable medium.
The demands on level switches can vary considerably, depending upon application. There are therefore numerous application-specific factors to consider, such as foam formation, aggressiveness or flammability of the media to be detected, adhesive substances, unfavorable installation conditions, the speed of the filling process and, naturally, the accuracy required.
The widely used vibrating forks do not necessarily offer the best conditions. Some have quite large components that extend far into the material being measured. Measuring errors can arise, since high viscosity materials tend to stick to these forks. Coarse granular media can easily become lodged between the forks and also cause measuring errors. The forks and difficult to clean and liquid and powder substances require different versions. It was impossible to cover all applications with one level switch, until now.
Versatile sensor with elegant configuration
Now the Baumer CleverLevel series of level switches fill this gap. They are based on frequency sweep technology. The sensor analyses the resonance frequency of the oscillating circuit affected by the dielectric constant of the medium below the sensor tip. This allows adhesive substance on the sensor tip or foam to be suppressed. High sensitivity over a large measurement range for dielectric constants from 1.5 to over 100 enables limit detection for all sorts of powders, granulates and liquids. And setup is easy.
The default setting already recognizes most media. The Teach-in function helps in case of doubt and more complex configuration becomes child’s play with the FlexProgrammer software, because the user can practically “see” the same thing as the sensor. The switching range can be adjusted as required to ignore foams in maximum or minimum monitoring, for example. The same applies if the sensor needs to ignore adhesive substances. Tanks with liquid chocolate are a typical example. Even when empty, the sensor and container walls are coated with chocolate. When configured accordingly, the CleverLevel still switches only when the tank is really full or empty. Electrostatic adhesion, which must frequently be taken into account in the detection of powdery substances, can also be ignored by appropriate definition of the switching range.
The simple, graphic configuration software really adds to the user-friendliness. For example, it is possible to observe the sensor’s internal signal while the thresholds are adjusted by mouse click within the graphic representation. This not only makes the configuration method intuitive and thus easily learned, but also considerably improves the reliability of the results, because they can be checked graphically at any time. This is also possible with extended setting methods that take medium conductivity into account, even if two media have the same dielectric constant.
Even different media in the same process line or process tank can be detected in order to differentiate the end product. For example, different types of fish sauce, different beers, etc. For this purpose a measuring signal can be output so that different dielectric constants through different media, foams or adhesive substances can be differentiated in the control. This makes it possible to detect if a medium is polluted with another medium, e.g. oil polluted with water.
Assessment of measurement results and maintenance planning
The information that is visualized with the help of software can also be transferred to the higher-level controller. It can then evaluate the measuring signal. It ultimately knows if the position of the switching point shifts because another medium is in the tank during flushing, for example. Dirt in the tank can also be detected in this way and cleaning can be scheduled accordingly. Today, many application areas are dependent upon this information. Wind power plants are a typical example of this, because “spontaneous” maintenance of lubricant containers is extremely costly and can only be carried out at unjustifiable expense. The same applies to locomotives, ships or mobile implements in agriculture, for example.
A further strength of the level-monitoring sensor is particularly evident in mobile tanks. It normally works with a response time of 0.1 sec., which permits high-speed filling processes and the precise maintenance of filling levels. However, this becomes a disadvantage if the tank is in motion and the contents slosh around. In such cases, a switching delay of up to 10 sec. can be set to avoid false signals due to tank movement.
Robust, hygienic, with ATEX approval
But the new CleverLevel series offers even more. The level switches can be installed in any position, even in rather inaccessible locations. The LED that signals the switching process is highly visible in all directions. The sensor works silently, compliance with protection class IP67 requirements is standard, and it is suitable for ambient temperatures between -40°C und +200°C. Operation is also unaffected by vibrations. For example, the latter is important if the level switch is placed close to a pump as protection against dry running. The small penetration depth of only 15 mm is also a positive feature in these circumstances. Flow and pressure are hardly affected. In addition, thanks to gap-free installation and the smooth tip, nothing can adhere to the sensor.
In addition to the industrial process connections, there are also versions with EHEDG approval and an ATEX version for Ex areas for applications with stringent hygiene requirements. There are countless application possibilities for this all-rounder level switch. The food and beverage industry can benefit from its possibilities as much as every other industry, from pharmaceuticals, chemicals, petrochemicals, and process engineering all the way to the water supply and wastewater fields. Further areas of application are found in wind power plants, mobile machinery, cereal mills or cleaning facilities and pumping systems.