The contents of this guide are intended to be used for pre-sales activities when a belt scale solution is being considered. The information required to
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2 Belt Scale Application Guidelines 2015 Siemens Level and Weighing Table of Contents Preface .. .. .. .. .. 1 Introduction .. .. .. .. 1 Belt Conveyor Te rminology .. .. .. 2 Belt Scale Selection .. .. .. .. . 2 Idler Detail .. .. .. .. 2 Locating the Sca le .. .. .. .. 3 Belt Tension .. .. .. .. .. 3 Material Turbulence .. .. .. .. .. 3 Curved Conveyors .. .. .. .. .. 4 Concave .. .. .. .. 5 Convex .. .. .. .. .. 5 Belt Ploughs .. .. .. .. .. 5 Training/Tracking Idlers .. .. .. . 5 Metal Detectors .. .. .. .. .. 5 Conveyor Tri ppers .. .. .. .. .. 6 Conveyor Considerations .. .. .. 6 Stacker Conveyors .. .. .. .. .. 6 Belt Scale Take – up Device .. .. .. . 6 Material Feed Point .. .. .. .. .. 7 Material Loading .. .. .. .. . 7 Without Control Gate .. .. .. . 8 With Control Gate .. .. .. .. .. 8 Material Roll Back .. .. .. .. .. 8 Conveyor Belting .. .. .. .. . 9 Belt Sag .. .. .. .. . 9 Belt Stiffness .. .. .. .. . 9 Idlers .. .. .. .. 10 Idler Alignment .. .. .. .. . 11 Idler Spacing .. .. .. .. 11
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3 Belt Scale Application Guidelines 2015 Siemens Level and Weighing Head Pulley .. .. .. .. . 11 Tail Pulley .. .. .. .. . 13 Conveyor Rigidity .. .. .. .. . 14 Vibration .. .. .. .. .. 14 Conveyor Covers .. .. .. .. .. 14 Temperature .. .. .. .. .. 14 Belt Tracking and Troughing .. .. .. . 15 Skirtboards and Sealing Strips .. .. .. .. 15 Belt scale verification .. .. .. 16 Main tenance and Modifications .. .. .. .. 17 Maintenance .. .. .. .. .. 17 Modifications .. .. .. .. . 17 Material Build – up .. .. .. .. . 17 Material Spills .. .. .. .. . 17 General Inst allation Requirements for Legal For Trade Applications .. . 18 General Conveyor Requirements .. .. .. 18 Product Selection .. .. .. .. .. 19 Belt Scale .. .. .. .. .. 19 Speed Sensor .. .. .. .. .. 19 Notes .. .. .. .. 20
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Preface The contents of this guide are intended to be used for pre – sales activities when a belt scale solution is being considered. The information required to properly size a belt scale does not take into consideration many of the other factors that are part of either the environment or the conveyor, which can lead to adverse performance if not properly managed or eliminated. Please refer to the appropriate belt scale operating instructions for full specifications, as well as installation and calibrat ion procedures. Manuals can be downloaded from the Siemens website at www.siemens.com/weighing When installed and applied according to the guidelines,. belt scale design and manufacture results in greater accuracy. To help the user maintain the accuracy a nd performance of the belt scale, this guideline provides recommendations for the proper application of belt scales under specific conveyor and environmental conditions. The guide is meant to be read chronologically to both teach and build on the knowledg e of how certain aspects of the application can compound with others to create poor performance from the scale. Note: All diagrams are specific to the Milltronics MSI belt scale. When applying this guideline to other belt scale models, use diagrams as exa mples only. Other belt weighing solutions are available including Microwave, Ultrasonic, Laser, Optical, and Gamma ray. These technologies are non – contacting, and therefore do not have the same point of reference as a gravimetric based belt scale which is the basis for this application guideline.
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Introduction Belt conveyor weighing can: Indicate flow rate of material during processing Totalize material for inventory monitoring Assist in loading of truck, ship, or rail car Assist in custody transfer Provide quality control for material batching Help monitor production A belt scale is a weighing solution that combines three components: 1. Scale Belt scales monitor the flow rate of material on a conveyor belt. 2. Speed sensor Spee d sensors detect the speed of the conveyor belt. 3. Integrator Integrators collect the data from the scale and sensor and output: Flow rate Belt load Belt speed Totalization Belt scales are generally not well suited to discrete weighing or check weighing applications or flow monitoring of batches or samples less than 10 minutes in duration.
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2 Belt Scale Application Guidelines 2015 Siemens Level and Weighing B elt Conveyor Terminology Belt Scale Selection Choose a belt scale that best suits your application, based on the following criteria: Maximum flowrate. Belt speed. Conveyor width, length, incline, pulley diameter, idler diameter, and trough angle. Use your application criteria to find an appropriate belt scale. Then, confirm your choice by checking the Scale Location and Conveyor Cons iderations starting on page 6. Idler Detail
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4 Belt Scale Application Guidelines 2015 Siemens Level and Weighing Recommendation Loca te the scale no less than one idler space beyond the point where turbulence stops. If that cannot be determined, refer to the following chart: Curved Conveyors Vertical curvature in the conveyor design can create difficulties with belt scales. Both concave and convex curvatures will disturb the idler alignment if the belt scale is installed in the area of the curve. The concave curvature is more difficult to manage because it may lift an empty belt off the idlers around the curve, preventing a good empty belt zero balance for the scale. The diagrams below illustrate the minimum distance the belt scale should be from the curvature to obtain accurate results.
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5 Belt Scale Application Guidelines 2015 Siemens Level and Weighing Concave Convex belt speeds d Belt Ploughs The use of belt ploughs or any conveyor or material control device that changes the profile of the carrying belt in or near the scale area is not recommended. These devices have a negative effect on the belt scale idler alignment, and may create drag on the belt which the scale may sense as a mater ial force or load. Recommendation Do not install the belt scale within 9 m (30 ft) of belt ploughs or similar devices that change the profile of the material or belt. Training/Tracking Idlers Training or tracking idlers help ensure the belt continues to stay centered on the conveyor. These special idlers are pivoted and force the belt from side to side when the belt mis – tracks. Recommendation Do not install the belt scale 9 m (30 ft) from a training or tracking idler. Metal Detectors
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6 Belt Scale Application Guidelines 2015 Siemens Level and Weighing Metal detectors create a magnetic field around the conveyor belt. This magnetic field can disrupt load cell signal processing. Recommendation Install the scale at least 3 m (10 ft) from any metal detectors or equipment that generates a magnetic field. Conveyor Trippers A conveyor with a tripper is not as common as a conveyor with fixed curvature, but it can have a similar effect on belt scales. A tripper can cause varying belt tension and can cause liftin g of the belt in the scale area if the belt scale is not located in the best position. Recommendation On a conveyor with a tripper, locate the scale according to the recommendations for fixed curves, but with the tripper in its fully retracted position. Conveyor Considerations Stacker Conveyors Any conveyor that is not a permanent structure or that varies in its incline, elevation or profile is not considered a good installation for an accurate belt scale. For applications where a belt scale can be used effectively with a conveyor of this type, please consult your Siemens representative. Recommendation Ensure that an inclinometer is used in applications with varying inclines and that accuracy will not normally achieve optimum specification. Belt Scale Take – up Device A variety of conveyor belt take – ups can control conveyor belt tension. Of the three basic types (screw, horizontal gravity, and vertical gravity), the vertical gravity take – up is the most reliable because it can react to changes in belt t ension and maintain relatively uniform tension. Using a vertical gravity take – up greatly reduces the influence of belt tension on the scale and improves accuracy.
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7 Belt Scale Application Guidelines 2015 Siemens Level and Weighing Recommendation For the best accuracy, use a vertical gravity take – up. If that is not practical or possible, use a horizontal gravity take – up. The use of the screw type take – up should be limited to conveyors with pulley centers of less than 18 m (60 ft). Material Feed Po int Some conveyor systems require that multiple feed points be in use at the same time. Belt tension can vary considerably depending upon the combination of feed points in use at any given time. Recommendation Whenever possible, install the scale on a c onveyor that has only one feed point. Material Loading Various methods are used to feed material to the belt. Often, the flow of material from the pre – feeder to the belt is not uniform and at speeds different from the conveyor belt speed. These influences may reduce accuracy.
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