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Level regulation without blemish Smart sensors in chocolate paradise
through non-metallic container walls without the sensor coming into contact with the media. However, conventional capacitive sensors also have a number of disadvantages. The sensitivity of the sensor must be adjusted in a time-consuming process so that the signal is triggered not by the container itself but by the container wall together with the medium. If you try to accurately detect the level of chocolate, ketchup or a similar substance using a conventional capacitive sensor, you will discover that these medias leave a residue behind when drained as well as regularly depositing, leading to sensing errors, making error-free measurement impossible. This challenge was faced by Gysi, the renowned
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chocolate manufacturer in Switzerland. They met this whilst seeking to equip the agitators of various tempering machines for heat treatment of chocolate when retrofitting new sensors for level regulation. The previous level detection system was based on measuring the pressure difference, was getting old and weathered and repeatedly had to be checked and cleaned at regular intervals. This incurred considerable effort and downtime. Therefore Gysi looked for a new solution. However, first attempts with a built-in sensor from the
machine manufacturer, did not look promising. "We couldn't leave the application unattended," says Ulrich Streit, who is responsible for the technology at Gysi, "the container kept overflowing. This was caused by sensing errors regarding the temperature range in which the tempering machine operated. All it took was a temperature change of a few degrees to change the permittivity of the medium in use, so much so that the sensor no longer switched correctly." “We then looked for an alternative and decided on a
sensor with smart level technology from sensor specialist Balluff. In making this decision we completely relied on Balluff," adds Streit. "Balluff provided us with a comprehensive consultation. Together we chose the right sensor based on the polarity of the medium to be measured—the chocolate—and then we checked it in a testing environment. It immediately worked. Now we have a solution that works completely error-free even in long- term operation."
apacitive sensors are a fine thing: They can detect levels of liquids, powders and granular materials
Measuring principle with many advantages "The new sensors in a M18 design operate according to the capacitive principle," explains Zumbrunn. "With strongly conductive media they open up new application fields whilst being significantly easier to handle. Therefore, they are capable of compensating for container walls and deposits, which enables error-free measurement without elaborate readjustments. Furthermore, they are also compatible with all sensors used for the level measurement of media having a dipole character. This applies to immersion applications and level detection through non-metallic walls with a maximum thickness of 10 mm. As a result, it is an easy task to detect the chocolate through a 3mm thick membrane of a plastic sleeve, in which the sensor is screwed into. This is possible due to sensors with smart level
technology operating at an oscillator frequency significantly higher than conventional capacitive sensors. Furthermore, the patented electronic processor unit gathers more information than is usually the case with capacitive level measurement. It evaluates not only the capacitance, but also the conductivity value of the medium. Since compact media has high, thin films of the same medium, but only low conductivity values, the new sensors have no trouble distinguishing between thin deposits and the real level. This means that sensing errors with media that do not drain without leaving residue, such as chocolate, are largely prevented. This technology was developed at the Balluff competence center for capacitive sensors, SIE Sensorik, headquartered in Viernheim, Germany.
Easy installation, fast adjustment Gysi now has 6 machines retrofitted with the new sensors and there are already plans to retrofit additional systems. "Since we do the conversion ourselves," Streit continues, "the expenses are low. The sensor is simply inserted into a sealed plastic sleeve and rotated into a separate metal container in the container wall ensuring that it is flush within the wall." The sensor with smart level technology is easy to adjust with a potentiometer, which has to be done only once after the installation. Furthermore, it operates without needing any maintenance whatsoever. Now cleaning procedures for just the sensor are entirely unnecessary; they are taken care of as part of the regular maintenance cycle.
CONNECTINGINDUSTRY.COM/IRISHMANUFACTURING IRISH MANUFACTURING | APRIL/MAY 2019 35 The sensor in the container wall detects the level of the
chocolate directly through the end face of the plastic sleeve in the container wall. If the chocolate falls below a certain fill level, the sensor triggers and after 30 seconds liquid chocolate is refilled until the optimum fill level is reached. Unlike conventional capacitive sensors, these fill-level
indicators do not have to be readjusted, neither during operation, nor when changing the recipe. Therefore, the switch point between white and dark chocolate, for example, differs by only three millimeters. "It is somewhat more expensive than a standard
capacitive sensor," summarises Ulrich Streit, "but when you find a perfect solution that works permanently, the price plays only a subordinate role. The device pays itself off within a very short time."
Balluff 01606 812 777
sales@balluff.co.uk
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