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New Technology provides a simple and more accurate method of moisture control

hether in the final pelletised product or the raw material intake, the moisture level in the material during animal feed manufacture is an essential value to measure and control. A number of different options present themselves when installing moisture control into a grain and feed processing plant. These include measuring the moisture of the incoming grain from the fields and also measuring moisture in the feed whilst it is in the mixer or after it has been pelletised. Moisture measurement is often viewed as too complex to add to a plant. Nuclear based and Near InfraRed solutions are expensive to install and maintain and microwave based moisture sensors have traditionally been seen as not accurate enough with limited information available when compared against the cost of the sensor. However recent developments in technology have enabled Hydronix, a UK based company which designs and manufactures digital microwave sensors, to include a set of new sensing modes within its latest generation of sensors. The new sensors take a digital measurement which is then processed to give a number of different readings relating to the electrical properties of the material. By selecting the measurement mode most appropriate to the material and process, a much more stable and precise reading of the moisture level can be obtained. Mechanical installation is also a very important consideration with microwave moisture sensors, as the consistency of the material and flow stability is crucial to getting the best results. The installations which achieve the best results have a bypass system which diverts some of the material flow past the sensor before returning it to the main flow. This prevents any interference from turbulence changes or changes in density in the previous processes affecting the moisture sensor. To assist customers to achieve the best results with mechanical installation, Hydronix has recently developed a new ducting system. This is designed to be inserted into 76 | March 2016 - Milling and Grain

existing plant ducting and is available for either vertical or angled ducting. This system enables a Hydro-Mix moisture sensor to be easily positioned at exactly the correct angle against the diverted material flow to achieve an extremely accurate, real time moisture measurement. Any adjustment that is required to the material flow is simple using the baffles provided. As digital microwave sensors provide a much more reliable and stable signal when compared with sensors based on older technologies, there is no need to continuously monitor and adjust the calibration of the material being measured. It is sufficient to make a calibration when the sensor is first commissioned and installed into the process. It is important to take representative samples from the process flow over the sensor at the same time as recording the average corresponding sensor values. This is vital, as these points will determine the accuracy of the material calibration point. Of equal importance is the testing of the material samples. It should not be assumed that another measurement technology is good enough to give an accurate moisture value, as other sensors are often not as accurate as they seem. The only scientific way to find the material moisture is to test the sample in the laboratory by heating it until completely dry and determining the loss in weight. The calibration process itself when using a digital sensor (which has a response which is inherently linear to the moisture change) is very simple. Each step change in moisture gives the same step change in the sensor reading. If you have two separate moisture sample points then you can extrapolate the calibration line very simply by doing a standard linear regression using the sensor setup software. This software also provides the option to add multiple calibration points which improves the accuracy of the sensors by cancelling out some of the inevitable errors due to sampling errors and laboratory handling procedures. As moisture is the simplest component to adjust during the manufacturing process, the addition of digital microwave sensors to a control system for a feed plant has now become a simpler, more accurate and extremely cost effective method for improving the final quality of the product.

Mar 2016 - Milling and Grain magazine  
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