How to control the density of fish feed


By Knut Szemjonneck, TEWS Elektronik knut.szemjonneck@tews-elektronik.com


When fish feed is put into water, it should act in accordance with the feeding behaviour of the respective fish. This means that it should either float on the surface or sink to the bottom. These characteristics largely depend on the fish feed’s density, which in turn defines the different types of fish feed: • Feed that floats on the surface of the water • Feed that sinks slowly • Feed that sinks and is water resistant • Feed that sinks and is extremely water resistant Consequently, the density of the fish flakes, granules, pellets or


chips is an important aspect for the quality of the product. The moisture content of the feed is also an important parameter for


the quality of the product throughout the production process. Both a high and a low moisture content often lead to loss of quality and can complicate further processing or even prevent it entirely. An ideal moisture content leads to a longer shelf life and prevents the onset of rotting. Regular checks of the moisture and density are therefore necessary


to produce high-quality fish feed. The common method of quality control is through laboratory measurements. Operators in the fish feed process are used to manually taking samples from production and analyzing the moisture and density content in a laboratory. This provides the respective moisture and density values that can, depending on the method, take between 5 minutes and a few hours to obtain. Sample taking is both time-consuming and labour-intensive, and the measured values are generally available too late to be able to control the production process adequately. TEWS Elektronik has developed a measurement technique with


which the moisture content as well as the density of the fish feed can be continuously measured during the production process. With the help of bypass sensors that are integrated into the process, the values are


Above: Bypass sensor for inline measurement of moisture and bulk density- filled with pellets.


measured and visualized reliably and accurately in a matter of seconds. A quick and targeted intervention in the production process is thus possible. Improved control of the production processes leads to energy savings as well as less wastage and better quality of fish feed. In short, moisture and density measurements during the process increase the efficiency of the entire production chain. The patented measuring method is based on microwave resonance


technology. As soon as the material passes through the field of the microwave sensor, its resonance properties change depending on the water content. A single configuration of the systems is all that’s needed for it to work continuously and reliably. The special unique feature of this technology is the independence of colour, density, grain size or surface influences of the product being measured. Contrary to the so-called near-infrared procedure, which measures the moisture content only on the surface, the microwave measurement equipment also determines the core moisture in the inside of the product, for example in pellets or granules.


Above: The MW 4260/70 enables the continuous inline measurement in processing lines. Up to 3,500 measurements per second are possible


PAGE 52 SEPTEMBER/OCTOBER 2017 FEED COMPOUNDER


The Microwave Resonance Method Water molecules are among the smallest molecules that are positively and negatively charged. The moisture sensor generates a low-energy electro-magnetic field, which interacts with these water molecules inside the product sample. Since the microwave field penetrates a few centimetres into the sample, water is not only detected at the surface but also in the product’s core.


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