Product Application Guidelines Platform Scales
Table of Contents Preface... 3 Introduction... 4 Platform scale selection... 4 Locating the scale... 5 Location... 5 Vibration... 5 Floor... 5 Bench... 5 Outdoors... 5 Scale considerations... 6 Balances... 6 Bench scales... 6 Floor scales... 6 Pallet truck scales... 6 Forklift scales... 6 Truck scales... 7 Rail scales... 7 Load cells... 7 End loading... 8 Mobility... 8 Cleaning... 9 Platform verification... 9 ANSI/ASTM E617 classes... 9 NIST classes... 10 Maintenance and modifications... 15 Maintenance... 15 Maintenance precautions:... 15 Material build-up... 15 Material spills... 15 Product selection... 15 Platform scale... 15 2
Preface The content of this guide is intended to be used for pre-sales activities when a platform scale solution is being considered. The information required to properly size a platform scale does not take into consideration many of the other factors that are part of the environment which can lead to adverse performance if not properly managed or eliminated. Please refer to the appropriate platform scale instruction manual for full specifications, and installation and calibration procedures. Siemens does not offer platform scales but can supply load cells and mounting units. For more information, go to our website at www.siemens.com/weighing. When installed according to these guidelines, platform scales will perform with greater accuracy. To help the user maintain the accuracy and performance of the platform scale, this guideline provides recommendations for the proper application of platform scales under specific environmental conditions. Note: All diagrams are specific to floor scales. When applying this guideline to other platform scale models, use diagrams as examples only. 3
Introduction Platform weighing can be used for: Shipping and receiving verification or indication Inventory control Truck/rail car loading Custody transfer Quality control for material batching Production monitoring A platform scale is a weighing solution that combines two components: a scale and a terminal. Platform scales weigh the material placed on them automatically or manually. Terminals collect the data from the scale and output weight. Platform scales are generally not well-suited to continuous weighing applications because the product being weighed is meant to be at rest during measurement. Platform scale selection Choose a platform scale that best suits your application, based on the following criteria: Maximum weight Required platform size. Stationary or mobile use Wash down conditions Material loading characteristics (e.g., steel coils require cradles) Use your application criteria to find an appropriate platform scale. Then confirm your choice by checking the scale location and application considerations below. 4
Locating the scale Location Select a location that is flat within ¼ (6mm), solid, level and that fully supports the weight of the platform scale plus the load that will be applied to it. Do not select a site where overweight loads would have to be maneuvered to avoid crossing the platform. Avoid areas where the scale might receive damaging shock loading from falling objects. Avoid areas where water or chemical spills could damage a scale not meant for a wash down environment. Vibration A platform scale is an inherently sensitive device and should be isolated from equipment that can induce harmful or disturbing vibration. Equipment such as crushers, vibratory feeding equipment, bins subject to hammering, and hammer mills should be avoided. Floor Floor scales can be mounted flush to the floor or on top of it. A floor scale that is mounted flush to the floor should be mounted on a rigid steel pit base. In wash down applications, this pit base should have a drain to ensure material does not become trapped below the scale. Scales mounted on top of the floor need to be protected from traffic and bumper guards are recommended. For platform scales on top of the floor where lift truck weighing is required a ramp will need to be installed to access the scale. The mounting feet of a floor scale are often adjustable for easy leveling. These feet should be restrained with mount plates so that the scale does not shift or move when items are placed on it. When ramps are installed, the scale feet should be connected to the ramp to ensure the scale doesn t shift when the load is applied. The floor scale must not be up against any obstruction that could hamper deflection as it will affect the performance of the scale. Install the scale in an area where it will be easy to access, with a clear indication that it is a scale to help protect it. Ensure that the terminal box is easily accessed for troubleshooting and maintenance. If the scale is mounted on the floor, ensure the floor is flat. If the area where the scale must be installed is not flat, self-aligning mount feet are also required. Tread plate should be used on scales that are flush to the floor for safe footing. Bench Bench scales can be mounted flush to the bench or on top of it. A platform scale that is mounted flush to the bench should be mounted on a rigid steel base. The mounting feet of a bench scale are often adjustable for easy leveling. The bench scale must not be up against any obstruction that could hamper deflection because this will affect the performance of the scale. Install the scale in an area where it will be easy to access. To help protect it, clearly indicate that it is a scale. Ensure that the load cell under the platform can be easily accessed for troubleshooting and maintenance. Outdoors Truck scales or any kind of platform scale installed outdoors must be able to withstand the natural elements. Truck or rail scales need to be installed on heavy duty concrete pads to ensure they can support heavy loads. In some cases, manhole access covers are required in the scale platform for maintenance and repair access. 5
Truck scales should be located so that the vehicle can enter and leave the scale as easily as possible. Smooth and level approaches are required at each end of the platform to reduce loading shock and facilitate testing of the scale. Rail scales must be installed in straight run sections where the rail car can be brought to a complete stop during weighing. The scale must not collect water above or below the platform; pooling water can affect weighing accuracy. Outdoor scales can be subject to harsh environmental conditions, including lightning strikes. Proper installation and maintenance are critical. Because truck and rail scales are often used for trade applications, optimum accuracy is important. Manufacturer s recommendations must be followed. Scale considerations Balances Balances can provide the highest level of accuracy for critical weighing and analyzing operations. With resolutions up to five decimal places, these scales can be used for inventory control or counting as well as verification of critical mixing and recipe control. Balances are typically small scales, with minimal capacities. Bench scales Scales used for table tops or benches are typically for critical micro tasks such as weighing materials for consumption or manufacturing. Bench scales can be certified to high legal-for-trade standards and are a very popular measurement device in commercial applications. Floor scales Floor scales are one of the most popular measurement instruments across all industries. Floor scales can be certified to legal-for-trade standards and can also be portable but are typically mounted on or in the floor. Different types of floor scales can be applied for different application needs, such as top deck hinged openings or materials of construction. Pallet truck scales Weighing pallets or skids, which can be easily transported, have made pallet truck scales popular in manufacturing. Not having to move the pallet to a floor scale for a weight reading, can save time and money. The scale is integrated into the lifting forks of the pallet truck. Pallet truck scales are generally not as accurate as floor scales due to their dynamic nature, but are often suitable for the purpose required. In-coming or outgoing logistics recording are suitable for pallet truck scales. Forklift scales The ability to weigh the item while transporting it has made forklift scales very popular in manufacturing and commercial industries. The scale is integrated into the lifting forks of the forklift. This eliminates the need to move items onto a floor scale or drive the entire forklift onto a scale for weighing. Forklift scales are generally not as accurate as floor scales due to their dynamic nature but are often suitable for the purpose required. In-coming or outgoing logistics recording are suitable for forklift scales. 6
Truck scales Truck scales are used to weigh materials being transported in trucks. The scale itself can weigh the entire truck on one bridge, or individual axles on multiple bridges. The smaller axle designs are much more cost effective than the complete bridge style. Truck scales are often certified legal-for-trade because the purpose is to sell the material based on its weight going into or out of the plant. Configurations of multiaxle scales are typically not accurate enough to be certified. The position of the scale can also be above ground or recessed into a pit depending on the customer s preference or environmental concerns. Becausetruck scales are subject to horizontal forces while the vehicle is moving across the scale, a small amount of movement is acceptable and will not damage the scale. Truck scales can often be used as the primary measurement in filling to determine load size as well as vehicle load weight. The soil bearing pressure must be adequate enough to support the scale, generally anything in the range of 7,300 kg/m² to 12,200 kg/m² (1,500 lb/f² to 2,500 lb/f²). The approach of the scale should be at least two times as long as the width of the scale for adequate ramping and smooth transition onto the bridge. Rail scales Rail scales are used to weigh materials being transported in train cars. The scale itself can weigh the entire car on one bridge, or individual axles on multiple bridges. The smaller axle designs are much more cost effective than the complete bridge style. Rail scales can be certified legal-for-trade because the purpose is to sell the material based on its weight going into or out of the plant. Configurations of multi axle scales are typically not accurate enough to be certified. Rail scales can often be used as the primary measurement in filling to determine load size as well as car load weight. The soil bearing pressure must be adequate enough to support the scale, generally anything above 12,200 kg/m² (2,500 lb/f²) is adequate. Load cells Depending on the type of platform scale, the load cell requirements will change. Bench scales are generally no larger than 24 x 24 (600mm x 600mm). For this reason, a single point load cell can be used mounted to the center of the scale. Single point load cells can handle capacities up to 1800 lb (800 kg). The load cell should be mounted so that the center of the cell is aligned to the center of the platform. Floor scales are generally no larger than 60 x 60 (1500mm x 1500mm). Platform scales use four load cells mounted at each corner of the scale. Shear beam load cells work best due to their low profile design and how the shear beam deflects, which allows for multiple cell mounting without mechanical binding or interference. 7
Truck scales can have anywhere from 6 to 12 load cells and can hold very large capacities, up to 40 t. Compression canister load cells are generally used for truck and rail scales. Compression type load cells require mounting units for proper alignment and installation. Ensure that any scale has the right load cell for capacity and environmental conditions. Multiple load cell scales should use self-aligning mounts to ensure that no mechanical binding occurs during deflection under load. End loading Floor scales should be rated for 100% end loading. End loading is an indication of how much weight can be applied to one side of the scale before any permanent damage can occur. Because many floor scales are used to weigh large pallets of material, the fork lift often places the weight down on one side to easily retract the forks and weigh the goods. 100% end loading ensures that the maximum rated capacity of the scale can be applied to one side of the scale safely. Ensure that any floor scales have a 100% end loading specification. Mobility Platform scales can be mobile or even part of a pump truck to weigh goods conveniently. Mobile platform scales of any kind must be zeroed before they weigh the goods to ensure that any influence of an uneven floor does not affect weighing accuracy. 8
Do not weight the goods while moving the scale. Ensure that any close obstructions to the scale are not in contact with the goods or platform, because this could affect scale accuracy. Mobile floor scales should have fork lift guides to ensure the forks do not damage the load cells during transport. Cleaning In applications where the scale will be cleaned, a lift top design is frequently most suitable because it allows for easy access below the platform. Drain holes or non-slip finishes are also available for flush mount units in wet environments. Ensure that scale and load cell construction is stainless steel. Load cells should be IP67 rated, as a minimum. Platform verification The best means of verifying a platform scale s performance is with certified weights. For applications thathave a high capacity rating, the use of weights is typically not practical. A weighed material sample can be use as the best alternative. Calibration test weights are a good choice for platform scale verification. The following standards apply to calibration weights: OIML R 111 classes OIML Class E0 - Used as a primary reference for calibrating other reference standards and weights where the stability of the environment and careful handling are assured. Class E0 weights have no method of adjustment and are not suitable for general laboratory use. Class E0 is 1/2 the tolerance of E1. OIML Class E1 - Used as a primary reference for calibrating other reference standards and weights where the stability of the environment and careful handling are assured. Class E1 weights have no method of adjustment and are not suitable for general laboratory use. OIML Class E2 - Can be used as a reference standard in calibrating other weights and is appropriate for calibrating high-precision analytical balances with a readability as low as 0.1 mg to 0.01 mg. OIML Class F1 - Appropriate for calibrating high-precision, top loading balances with a readability as low as 0.01 g to 0.001 g. OIML Class F2 - For calibration of semi-analytical balances and for student use. OIML Class M1, M2, M3 - Economical weights for general laboratory, industrial, commercial, technical and educational use. Typically fabricated from cast iron or stainless steel. ANSI/ASTM E617 classes ANSI/ASTM Class 000 - Used as a primary reference for calibrating other reference standards and weights. Class 000 weights are intended to be used in metrology laboratories where the stability of the environment and careful handling are assured. Although very stable, one-piece construction Class 000 weights have no method of adjustment and are not suitable for general laboratory use. 9
ANSI/ASTM Class 00 - Used as a primary reference for calibrating other reference standards and weights. Class 00 weights are intended to be used in metrology laboratories where the stability of the environment and careful handling are assured. Although very stable, one-piece construction Class 00 weights have no method of adjustment and are not suitable for general laboratory use. Class 00 weight tolerances are equal to OIML R 111 E1 tolerances and are tighter than Class 0. ANSI/ASTM Class 0 - Used as a primary reference for calibrating other reference standards and weights. Class 0 weights are intended to be used in metrology laboratories where the stability of the environment and careful handling are assured. Although very stable, one-piece construction Class 0 weights have no method of adjustment and are not suitable for general laboratory use. ANSI/ASTM Class 1 - Can be used as a reference standard in calibrating other weights and is appropriate for calibrating high-precision analytical balances with a readability as low as 0.1 mg to 0.01 mg. ANSI/ASTM Class 2 - Appropriate for calibrating high-precision top loading balances with a readability as low as 0.01 g to 0.001 g. ANSI/ASTM Class 3 - Appropriate for calibrating balances with moderate precision and with a readability as low as 0.1 g to g. ANSI/ASTM Class 4 - For calibration of semi-analytical balances and for student use. ANSI/ASTM Class 5 - For student laboratory use. ANSI/ASTM Class 6 - This class meets the specifications of OIML R 111 Class M2. ANSI/ASTM Class 7 - For rough weighing operations in physical and chemical laboratories, such as force measuring apparatus. NIST classes NIST Class F - Primarily used to test commercial weighing devices by state and local weights and measures officials, device installers, and service technicians. Class F weights may be used to test most accuracy Class III scales, all scales of Class IIIL or IIII, and scales not marked with a class designation. The following table lists the tolerances of weights that could be used in platform scale applications: Calibration weights should be used to meet the needs of the application and not exceed it. The accuracy of the scale should be taken into consideration as well. 10
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Maintenance and modifications Maintenance Once the scale is installed it requires little to no maintenance. Maintenance precautions: When welding near the scale, do not allow current to pass through the load cells. Reset the shipping stops to reduce physical shock to the load cells during maintenance. Material build-up Keep the scale and associated equipment as clean as possible, so that the scale measures only the loads intended and not the added load due to material sticking to the scale. To remove materials that stick to the scale equipment, use a vacuum to remove solids or washer for cleaning. Although scales can be frequently and automatically recalibrated at no load (zero), it is not a good practice to allow material build-up to remain on the scale. Material spills General good housekeeping is always important. Material spillage results in lost production and can also adversely affect scale operation when spilled material wedges between dynamic parts preventing proper scale deflection. In addition, the build-up affects the zero balance of the scale. Do not overload the scale. As a precaution, install deflectors to keep spills from reaching the scale. Product selection Platform scale There are many different styles of platform scales available: bench, floor, truck designs, industrial or commercial with multiple platform styles. Generally, there are three factors to consider when selecting a platform scale: Application needs Price point Drives the specific selection of models and options. The environment will also play a part, the scale should be stainless or galvanized in corrosive areas or near sea ports. If the location is considered hazardous, an approved scale will be needed. Influences the selection of the type of scale. Featureless scales are less expensive, but if the application is not suited for them, they should not be used. Scale sizing Limitations based on application needs and product features or performance will narrow the selection of the product in most cases. Load size and load cell optimization are all considered when a platform scale is engineered. 15
Siemens AG Industry Sector 1954 Technology Drive P.O. Box 4225 Peterborough, ON Canada K9J 7B1 email: techpubs.smpi@siemens.com For more information www.siemens.com/weighing