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STORAGE EQUIPMENT How to ensure accurate grain level measurement with grain applications, Hycontrol engineers have found ccuracy, repeatability to TDR guided wave radar units to be more suitable and reliability are and more reliable than competing technologies for essential concepts this product. in the field of level VF04 TDR gauge TDR Technology control. Without Originally developed for detecting breaks ensuring these key in subsea cables, TDR (Time Domain requirements are Reflectometry) technology has proven to met by whichever be a powerful tool for level monitoring and level monitoring control. The TDR unit is mounted on top of equipment is being deployed, producers risk the storage vessel with a probe guide (usually a running out of product (leading to production cable or rod) hanging down inside the vessel. During stoppages and downtime) or, worse, overfilling operation, micro-pulses are transmitted along a probe their storage vessels (with the risk of product loss, guide. The pulse travels at close to the speed of light, pollution and costly clean-ups). This is as true in the and when it hits the grain surface much of the energy storage of grain as it is in the storage of cement, sand, is reflected back to the electronics module on top of the sugar, or anything else from a long list of bulk products. vessel. Working on the principle of ‘time-of-flight’ this It is therefore in the best interest of site operators and information is then converted to provide readings of the producers to firstly know how their grain will behave in level, distance or volume, depending upon what is required the storage vessel, and secondly to utilise quality, up-toby the site operators. date level monitoring equipment. The advantages of choosing TDR for grain measurement Achieving accuracy and repeatability applications are numerous. Whereas many non-contact The first step in establishing an accurate and repeatable level measurement technologies can be disrupted by dust level measurement output on a grain storage vessel inside the vessel and provide false readings, TDR remains is through the positioning of the level probe itself, unaffected by dust, coating or changes in temperature. It is specifically in relation to the fill point. Assuming there is durable and reliable, and largely immune to the issues of a single, centrally-located, fixed fill point, solid material mechanical wear and tear that affect pulley-based systems being fed into the vessel – in this case, grain – will behave and other older contact technologies. Above all, TDR in a fairly predictable manner, coming to rest in a conical technology offers a high degree of repeatable accuracy for pile that peaks beneath the fill point. The so-called ‘angle solid products and should require only periodic routine of repose’ (the slope of the pile when the falling product calibration and cleaning. has come to rest) will vary according to the properties of With the launch of the new VF04 TDR gauge, Hycontrol the product and the size of the vessel but should be around has produced a compact, durable TDR unit ideally suited 45°. Similarly, when the grain is drained from below one to the needs of the milling and grain industry. With a can expect to see a similar depression forming. variety of probe types offering a measurement range of up Of course, there are many factors that will have an effect to 24 metres and accuracy of +/- 5 mm, this two-wire loop on the behaviour of the product in the vessel, including its powered unit has been designed for simple installation density, the shape of the vessel, variances in the pressure and can be retrofitted to existing process connections. at which the product is blown in, and so on. That said The unit can be easily configured on-site using the plugthe use of simple geometry would provide a useful guide in LCD programming and display unit; information can for positioning a level probe so that it can take a reliable then be piped to a central site PLC via the 4-20mA or HART average of the grain cone height within the vessel. outputs. Alternatively, a HART programmer or a computer with Hycontrol engineers, drawing on the company’s extensive appropriate PC software can be used to remotely programme the experience in the level measurement field, recommend mounting unit. continuous measurement probes at a position approximately Many grain industry applications will be in designated 2/3rd radius of the vessel away from the product peak position hazardous areas, and accordingly, the VF04 is available with that forms after a fill. Even in vessels that experience constant ATEX Ex ia options. For level monitoring in production filling and draining, this provides a reliable indication of the processes, there are also high-temperature models and coated content level to users. Please note that behaviour of product in cables for measuring more aggressive products. Besides grain vessels with multiple fill and drainage points is often harder and other similar solid products such as flakes and powders, the to predict, which may adversely affect contents measurement VF04 TDR can also be used with liquids, slurries and pastes. accuracy. Consultation with an experienced level measurement Through the deployment of well-positioned, well-chosen company is therefore advised. level measurement technology, site operators and management As previously mentioned, the correct selection of technology can be confident in the accuracy and reliability of their level is equally as important as the positioning of the probe. Anyone measurement readouts. This, in turn, will help to ensure with even a cursory knowledge of level measurement and control continued production efficiency and more importantly will assist equipment would agree that that the variety of options available in the prevention of costly incidents in grain storage vessels. can appear overwhelming. Therefore it is wise to draw on the experience of industry veterans. In over three decades of dealing

82 | April 2017 - Milling and Grain

APR 2017 - Milling and Grain magazine  
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