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High-precision sensors: the ideal solution for measuring grain humidity


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Storing and manufacturing food materials like grain can be extremely challenging. Even the slightest bit of extra humidity can create mould growth, causing the grain to deteriorate. This leads to …

Storing and manufacturing food materials like grain can be extremely challenging. Even the slightest bit of extra humidity can create mould growth, causing the grain to deteriorate. This leads to economic losses for manufacturers in the commercial food industry.

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  • 1. Digital Re-print September | October 2013 High-precision sensors: the ideal solution for measuring grain humidity Grain & Feed Milling Technology is published six times a year by Perendale Publishers Ltd of the United Kingdom. All data is published in good faith, based on information received, and while every care is taken to prevent inaccuracies, the publishers accept no liability for any errors or omissions or for the consequences of action taken on the basis of information published. ©Copyright 2013 Perendale Publishers Ltd. All rights reserved. No part of this publication may be reproduced in any form or by any means without prior permission of the copyright owner. Printed by Perendale Publishers Ltd. ISSN: 1466-3872
  • 2. FEATURE Figure 1: Microwave resonator with inner lens tube High-precision sensors: the ideal solution for measuring grain humidity by Hinrich Römhild, sensors and measurement senior R&D engineer, WORK Microwave GmbH, Germany S toring and manufacturing food materials like grain can be extremely challenging. Even the slightest bit of extra humidity can create mould growth, causing the grain to deteriorate. This leads to economic losses for manufacturers in the commercial food industry. Microwave resonator-based sensors offer a solution to this problem by enabling manufacturers to obtain a precise measurement of the weight, moisture, or water content of grain. Moreover, microwave sensors can also be used to identify foreign particles or substances that have come into contact with grain. This article explains the benefits of relying on microwave frequencies and RF resonators to accurately measure the humidity of grain. 38 | September - october 2013 Measuring grain humidity In the food manufacturing business, if grain materials are exposed to too much humidity, they can develop mould and would then need to be discarded. This can be prevented by controlling the humidity within the Key for Figure 2: ¢ Oats ¢ Triticale ¢ Barley ¢ Wheat Figure 2: Resonance curve for different samples of grain &feed millinG technoloGy Grain
  • 3. FEATURE production facility using microwave frequencies and RF resonators. Resonators are high-quality factor (Q factor) structures that resonate at specific frequencies. When a sample of the grain material is inside of the cavity region, it affects the cavity’s centre frequency and Q factor. The material’s electrical permittivity and permeability are determined using the frequency shift between the resonant frequency of the unloaded resonator (f Res unloaded) and the loaded resonator (f Res loaded). The Q factor is calculated based on the frequencies from 3 dB to the magnitude at resonance. Measuring the shift in resonance frequency and Q factor helps to determine two corresponding physical qualities, such as weight and humidity. In many cases, only one physical measurement is required, necessitating the resonator to only measure the shift in resonance frequency or the Q factor. A typical resonator measurement system using the resonant cavity method includes a resonator cavity, signal processing part, and software control by a computer. For this specific application, the resonator is aluminum-based and has a diameter of about 22 cm and a height of approximately 32 cm (Figure 1). The electrically active part is supplemented by two flanges on the top and the bottom. They enable integration in a tube system and avoid any discharge of electromagnetic radiation. The aluminum resonator also features a tube made of PEEK. PEEK, or PolyEtherEtherKetone, is a type of plastic approved for appliance in food technology. It is extremely resistant to chemicals and offers a heat resistance to 480°F. Thus, a PEEK tube does not degrade after being exposed to water or steam and is flame- and radiation-resistant. Unfilled PEEK received FDA approval in 1998 and may be used in food contact and in processing equipment without danger of contamination or degradation. In an aluminum resonator with a PEEK tube, the grain only encounters the PEEK tube, ensuring the materials are not compromised. The plastic tube of the sample resonator has an inner diameter of 62 mm. For measurement of electrical characteristics, the resonator includes two small antennas. One is used for sending microwave signals, the other for receiving. In order to analyse the data from the antennas, the absorption of the microwaves on their way from the transmitting antenna to the receiving antenna needs to be contemplated. Thus, the resonator is connected to an evaluation unit. A laptop shows the transmittance measured. By applying the microwave transmittance over the frequency, users can determine a maximum with a frequency of 1050 MHz in an empty test resonator. If the user fills grain in the resonator, this maximum will be shifted to lower frequencies. This makes it possible to distinguish between different kinds of grain (Figure 2). &feed millinG technoloGy Grain Making the same adjustment, it is also possible to distinguish between samples of the same grain with diverse humidity. Figure 3 shows the differences between various wheat samples. The curves received are easily reproducible. The analysis shows that changes in humidity are detectable in a one-tenth percent range without any problems. Examination of the complete resonator curve is not feasible in the field. Therefore, the output of the sensors has been limited to the transmittance of one frequency. In this instance, only one value corresponds with the humidity of grain. In order to demonstrate the measurement process an adjustment was made (Figure 4). Figure 4 shows a tube of acrylic glass with three samples of grain with different humidity. The samples are physically fastened by foam bucklers. The measurement reading is the transmittance on a working frequency while the test tube is pushed through the resonator. Figure 5 shows the measurement result over time. The samples of grain can be distinguished clearly. The minima arise if the foam is in the active area of the resonator. Analog & Digital RF-Solutions Precision Sensors for the production environment Typical Applications Mass / Weight Optimize your Production Process with Microwave Sensors »» Microwave technology measuring principle »» Ideal for demanding in-line applications »» Suitable for solid, granular and Moisture powdered materials »» Measures samples as small as 1 mm³ »» Up to 10,000 samples per second Foreign Particles »» Rugged housing for harsh environments »» Contactless and maintenance free measurement »»Contact us Address: Tel.: Fax: E-Mail: Web: WORK Microwave GmbH Raiffeisenstraße 12 83607 Holzkirchen – Germany +49 8024 6408 0 +49 8024 6408 40 September - october 2013 | 39
  • 4. FEATURE Figure 4: Measurement adjustment in humidity Key for Figure 3: ¢ Wheat humidity 14% ¢ Wheat humidity 18% ¢ Wheat humidity 20% Figure 3: Resonance curve for wheat with diverse humidity The sensor (including local electronic) can be easily integrated in a transport system of a grain dryer. Analysis can then be performed on a local laptop or on a PC at a central location via ethernet connection. Of course, a custom-built adaptation on the type of dryer in question is necessary. Benefits of microwave resonator technology In addition to helping food manufacturers accurately measure the humidity of grain, microwave resonator sensors offer a number of other benefits. One is the ability to measure extremely small samples (e.g. as small as 1 mm3) with precision accuracy at high speeds of 10,000 samples per second. Given the small size of grain, this is important on a manufacturing line. Microwave resonators are also highly sensitive, making it possible to detect small differences of the unloaded resonator while the probe is on. This is critical to measuring the humidity of grain with the utmost accuracy. The repeatability of a microwave resonator is about 0.1 percent, indicating that the variation in measurements taken by a single sensor is quite low and that an accurate measurement is being taken. The microwave resonator technique is also much safer and more cost-effective than using nuclear-based sensors. In the food industry, consumer safety is of utmost concern. Nuclear sensors contain radioactive material, requiring manufacturers to train their employees about the proper protocols involved with handling radioactive materials. Nuclear sensors also require a strict waste disposal process that is heavily regulated by the government. Conclusion Figure 5: Sensor signals for wheat with different humidity (14, 18 and 20 %) 40 | September - october 2013 Food manufacturers have a responsibility to deliver the freshest quality product possible to consumers. A microwave resonatorbased sensor allows them to achieve this by performing real-time, accurate measurements of the weight, moisture, and water content of grain. Microwave resonator sensors can easily be integrated into any manufacturing facility to increase productivity and profits. While this article specifically addressed the use of microwave resonator technology for grain, RF sensors based on the microwave resonator technique can also be used to measure other food materials. They can also be applied in other industries, such as tobacco, pharmaceutical, automotive, recycling, and chemical to measure moisture, mass, and density, as well as to identify foreign particles and measure dielectric properties. &feed millinG technoloGy Grain
  • 5. LINKS September - October 2013 This digital Re-print is part of the September | October 2013 edition of Grain & Feed Milling Technology magazine. Content from the magazine is available to view free-of-charge, both as a full online magazine on our website, and as an archive of individual features on the docstoc website. Please click here to view our other publications on first published in 1891 • The holistic approach to avoid losses in the feed mill In this issue: • • Sieving technology in feed pellet production • Mixed integer optimization: Traceability a new risk in maize production? • See the full issue • Visit the GFMT website • Contact the GFMT Team • Subscribe to GFMT a new step in formulation software • Weighbridges the workhorses of industrial weighing • High-precision sensors: the ideal solution for measuring grain humidity INCORPORATING PORTS, DISTRIBUTION AND FORMULATION A subscription magazine for the global flour & feed milling industries - first published in 1891 To purchase a paper copy of the magazine, or to subscribe to the paper edition please contact our Circulation and Subscriptions Manager on the link adove. INFORMATION FOR ADVERTISERS - CLICK HERE Article reprints All Grain & Feed Milling Tecchnology feature articles can be re-printed as a 4 or 8 page booklets (these have been used as point of sale materials, promotional materials for shows and exhibitions etc). If you are interested in getting this article re-printed please contact the GFMT team for more information on - Tel: +44 1242 267707 - Email: or visit