USB Load Cell with Analog and Digital Output

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Load Cell Terminology

Ambient Conditions		The conditions (humidity, pressure, temperature, etc.) of the medium surrounding the load cell.
Ambient Temperature		The temperature of the medium surrounding the load cell.
Angular Load Eccentric		A load applied eccentric with the primary axis at the point of application and at some angle with respect to the primary axis.
Angular Load Concentric		A load applied concentric with the Primary axis at the point of application and at some angle with respect to the Primary axis.
Axial Load		A load applied along or parallel to and concentric with the primary axis.
Calibration		The comparison of load cell outputs against standard test loads.
Calibration Curve		A record (graph) of the comparison of the load cell outputs against standard test loads.
Combined Error		(Non linearity and Hysteresis) The maximum deviation from the straight line drawn between original no-load and rated load outputs expressed as percentage of the rated output and measured on both increasing and decreasing loads.
Compensation		The utilization of supplementary devices, materials, or process to minimize known sources of error.
Creep		The change in load cell output occurring with time while under load and with all environmental conditions and other variables remaining constant.
Creep Recovery		The change in no-load output occurring with time after removal of A load which had been applied for a specific period of time. Usually measured over a specific time period immediately following removal of rated load and expressed as a percent of rated output over a specific period of time.
Deflection		The change of length along the primary axis of the load cell between no-load and rated load conditions.
Drift		A random change in output under constant load conditions.
Eccentric Load		Any load applied parallel but not concentric with the primary axis.
Error		The algebraic difference between the indicated and true value of the load being measured.
Excitation, Electrical		The voltage or current applied to the input terminals of the load Cell.
Frequency Response		The range of frequencies over which the load cell output will follow the sinusoidally varying mechanical input within specified Limits.
Hysteresis		The maximum difference between load cell output readings for the same applied load; one reading obtained by increasing the load from zero and the other by decreasing the load from rated output.
Insulation Resistance		The dc resistance measured between the load cell circuit and the load cell structure. Normally measured at fifty volts and under standard test conditions
Load		The weight or force applied to the load cell.
Load Cell		A device which produces an output signal proportional to the applied weight or force.
Natural Frequency		The frequency of free oscillations under no-load load conditions.
Nonlinearity		The maximum deviation of the calibration curve from a straight line drawn between the no-load and rated outputs; expressed as a percentage of the rated output and measured on increasing load only.
Output		The signal (voltage, current, pressure, etc.) produced by the load cell. Where the output is directly proportional to excitation, the signal must be expressed in terms of volts per volt, per ampere, etc., of excitation.
Output, Rated		The algebraic difference between the outputs at no-load an at rated load.
Overload Rating, Safe		The maximum load in percent of rated capacity which can be applied without producing a permanent shift in performance characteristics behond those specified.
Overload rating, Ultimate		The maximum load in percent of rated capacity which can be applied without producing a structural failure.
Primary Axis		The axis along which the load cell is designed to be loaded; normally its geometric centerline.
Rated Capacity (Rated Load)		The maximum axial load the load cell is designed to measure within its specifications.
Reference Standard		A force measuring device whose characteristics are precisely known in relation to a primary standard.
Repeatability		The maximum difference between load cell output readings for repeated loadings under identical loading and environmental conditions.
Resolution		The smallest change in mechanical input which produces a change in the output signal.
Sensitivity		The ratio of the change in output to the mechanical input.
Shunt Calibration		Electrical simulation of load cell output by insertion of known shunt resistors between appropriate points within the circuitry.
Shunt-To- Load Correlation		The difference in output readings obtained through electrically simulated and actual applied loads.
Side Load		Any load acting 90 degrees to the primary axis at the point of axial load application
Stabilization Period		The time required to insure that any further change in the parameter being measured is tolerable.
Standard Test Conditions		The environmental conditions under which measurements should be made when measurements under any other condition may result in disagreement between various observers at different times and places. These conditions are as follows: Temperature 23 degrees +or- 2 degrees C (73.4 degrees +or- 3.6 degrees F
Temperature Effect On Rated Output		The change in rated output due to a change in ambient temperature.
Temperature Range Compensated		The range of temperature over which the load cell is compensated to maintain rated output and zero balance within specific limits.
Temperature Range Safe		The extremes of temperature within which the load cell will operate within permanent adverse change to any of its performance characteristics.
Terminal Resistance Corner To Corner		The resistance of the load cell circuit measured at specific adjacent bridge terminals at standard temperature, with no load applied, and with the excitation and output terminals open-circuited.
Terminal Resistance Input		The resistance of the load cell circuit measured at the excitation terminals at standard temperature, with no load applied and with the output terminals open-circuited.

Content source: transducertechniques.com

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Making of a Resistive Load Cell

Designing
Depending on the application the type (bending beam, column, shear beam, etc.) is decided. Load range and the output are important factors to consider while deciding the material to be used. While aluminum is used for lower load ranges steel is preferred for higher loads. For weigh scale applications bending beam load cells are used. Tensile loads cells are used in automatic packing machines to measure tensile forces. High capacity column or shear beam load cells are used for weigh bridges/truck scales.

A load cell designing software reduces work to a great extent. Most software provide dimensions for the most critical part of the load cell. For shear beam load cells web thickness is most critical. For column load cells column width and width is important. And for binocular beam load cells thickness of the thinnest part of the profile & distance between the holes are important.

Material Procurement
Material procurement involves purchase of metal (steel or aluminium), strain gauges (transducer class), bonding adhesive, terminals, PCBs, cables, bellows, fasteners and name plates.

Strain gauges are selected based on the application; linear or shear. Strain gauges are available in various sizes such as 3mm, 6mm, etc. Strain gauges can be procured from any of the reputed manufacturers like HBM, Micro-Measurements (MM), Shinkoh, BLH, etc. Bonding adhesive and matching accessories such as terminals, wires for internal wiring, cable glands, etc. are also procured. Teflon coated multi-core cable (4 core or 6 core) with right color code (red, black, white, green, yellow and blue) is procured from the right vendor. Cable should be tested for continuity and also quality of strands within the cores, strands should be silver-coated and flexible.

Alloy with right cross section (circular or square or rectangular) is selected so that material wastage is at its least. Most manufacturers prefer to use circular sections of EN24 for steel load cells. Next step is testing the metal's chemical composition and internal cracks (ultra sound testing) from a reputed testing services provider. Alloys not confirming to industry standards is rejected. Also material with internal cracks cannot be used for load cell manufacturing.

Machining and Heat Treatment
Machining raw material to required form is performed with lot of care. Commonly used machines are shaping machine, milling machine, lathe, column drilling machine and surface grinding machine. Machines should be in good working conditions and capable of producing accurate dimensions. Right coolant is used at all stages to avoid excessive heating during the process. Dimensions are checked at every stage using precision measuring instruments such as height gauge, digital vernier, depth gauge, micrometer, etc. at accuracy of 1 micron. Material in process (steel) is oiled to avoid oxidation. Surface grinding is the last stage of machining, its done after the process of hardening.

Only steel elements undergo the process of hardening at a heat-treatment plant. The elements are heated slowly to a high temperature and cooled rapidly in a oil bath followed by further cooling in a water bath. Harness is tested in a Rockwell Hardness Tester. Hardness value should be between HRC 40 to 45. If the value is lesser than 45 then elements need to be hardened again or if the value is higher than 45, elements will be softened. Some batches of steel fail to harden to the required value, elements have to be rejected in such cases.

Surface grinding achieves two objectives; accurate dimensions and smooth surface finish. Material removed in the process is usually few microns. The elements undergo one last round of deburring and ready for the next stage.

Electroplating
Zinc-plating was the used commonly during earlier years. However in the last 2 decades electroless nickel is the preferred protective coating since it offers good protection and also makes the elements aesthetically good. Elements undergo a process called buffing to improve the surface finish. Then it is cleaned and rinsed in chemicals to remove grease and other matter. Elements are kept dipped in a chemical bath for a specified period of time during which nickel adheres to the elements. The last step is polishing which is done to enhance aesthetics.

Bonding Strain Gauge and Internal Wiring
This is a crucial stage of load cell manufacturing. On the element, the surface where strain gauge is to be fixed is prepared by polishing it with water emery in circular movement. Using a height gauge and a surface plate the cross-hairs are drawn to mark the precise position of the strain gauge on opposite sides of the element. The strain gauge surface is cleaned thoroughly using chemical agents like Trichloroethylene (TCE) and Acetone. Alternate chemicals are used in place of TCE since its banned in many countries.

Once the element is free from grease and other impurities, adhesive is applied at the cross-hairs (matching the approximate area occupied by the strain gauge). Adhesive is also applied to the bottom-side of strain gauges and solder terminals and allowed to settle for few minutes. Its important to apply just the right amount.

Under a microscope, the strain gauge is positioned by aligning the marks with the cross-hairs and then taped to hold it in position. The adhesive tape used is of special quality capable of withstanding temperatures in the range of 250 degrees Centigrade for about 2 hours. With strain gauges in places, pressure pads and clamps are fixed. This is done to arrest movement and also maintain uniform thickness of adhesive between the strain gauge & element. With clamps in position, elements are placed in an electrical oven (with a air blower) and heated to about 180 degrees for about one hour. The process is usually known as curing. Temperature and duration of heat treatment depend on the adhesive used. The elements require about 12 hours to cool down to room temperature and should happen naturally. After curing, clamps and adhesive tapes are removed. The elements undergo another round of heat-treatment called post-curing. This done to destress starin gauges and adhesive.

The next step is to solder strain gauge terminals to solder tabs and fix wires to create a circuit so that the strain gauges are in Wheatstone Bridge configuration. High-end soldering stations (temperature controlled) with special solder tips are used for this job. The internal wiring terminates at a small PCB to which the multi-core cable is joined. At this stage, we have a working load cell. A basic test is done; 10V DC (or 12V DC) is applied is measured using a multimeter with least count 0.1V and no-load or zero output is noted. Load is applied in right direction to check if output is positive. Ideally no-load is adjusted to -0.25 mV.

Temperature Compensation
Load cells are required to behave consistently through a specified temperature range ~ 0 to 60 degrees Centigrade. To achieve that, load cells are studied at 0°C and 60°C for 6 to 12 hours. Based on the differences in output, a length of wire made of a special alloy is introduced into the circuit to counter the effect of temperature. A second round of temperature test is run to ensure the load cell behavior is constant through out the range i.e. between 0°C and 60°C. With recent developments in strain gauge technology, self-compensating strain gauges have eliminated one stage of load cell manufacturing. However, companies serious about quality do check load cell behavior at different temperatures.

Load Testing and Calibration
In this stage, load cells undergo a host of tests- full scale output, repeatability, linearity, creep, hysteresis, and many more. Load cell output is tuned to 20mV (or 10mV, 30mV depending on the specification) at rated load. Load cells also undergo overload tests to ensure they withstand 150% of the rated load.

Repeatability Test: Load cell undergoes full scale (and partial load also) test number of times and output noted at every instance of loading. The output should be within the claimed accuracy level.

Linearity Test: Load cell undergoes incremental & decremental loading and output noted at every instance. The Load versus Output graph should be a straight line.

Creep Test: Load cell is loaded at full scale for an extended period, say one hour, and the out output is observed. Ideally the output should neither increase nor decrease.

Hermetical Sealing
This is the final stage where the load cell is made dust-proof, moisture-proof and water-proof. Some lower-end load cells are not hermetically sealed for cost reasons. Larger load cells (higher capacities) are coated with expoxy paint to provide additional protection. The load cell is tested again to ensure that outer cover or bellow has not affected load behavior.

Every load cell is supplied with a data-sheet which has load cell serial number, date of manufacturing, cable color code, external dimensions and electrical parameters like excitation voltage, input & output impedance, no-load output, rated capacity, full scale output, sensitivity, etc.


For definitions of load cell terminology, please refer this webpage- http://www.transducertechniques.com/load-cell-terminology.cfm

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Things to consider before buying a load cell

When your application needs to measure static or quasi-static loads, forces or weights, you would need to use a load cell. A load cell is a device that converts the applied force into an electronic signal that can be used to compute the magnitude of the force applied. Although relatively simple in concept, you’ll find that there are many complexities that might affect measurements when you actually implement your load cell system. One needs to consider a number of factors before you decide which load cell to use. These include:

1. Magnitude of force/load/weight being measured
   • This is important to know because typical load cells offer overload protections of about 1.5 times the rated load capacity. If you apply loads – even temporarily – beyond this maximum load – you can seriously damage your load cell and might need to recalibrate it to ensure accurate readings
   • If you suspect that there could be an occasional spike in loading conditions, be conservative in picking a load cell with adequate capacity to handle the highest load condition with at least 50% margin to avoid exceeding the elastic limit of the load cell
2. Accuracy needed for application
   • Accuracies of load cells are generally rated as a percentage of full scale. So a load cell with 0.1% accuracy rating for a 100 lb load cell would offer +/- 0.1 lb accuracy, but the for a 1000 lb load cell offer a +/- 1 lb accuracy. So you need to pick the right capacity load cell for your application
   • Certain test and measurement applications may need the accuracy as a percentage of reading so you may need to pick a load cell with adequate accuracy to address those applications
   • You also need to consider the accuracy of the complete system – not just the load cell. Depending on how you plan to use the load cell, the accuracy of the system could be a function of the load cell, the signal conditioning equipment, the resolution of the digitizer, the variation of the power being supplied and other environmental factors
3. Operating Temperature Conditions
   • Although most load cells offer certain degree of temperature compensation, you need to consider the operating conditions before you pick a load cell.
   • Is your application in a well controlled, room temperature or outdoor, harsh environments with changing humidity and temperature? If it is outdoor – you should look for load cells with IP68 rating
   • Even with temperature compensated load cells, there could be transient temperature conditions that affect the load cell readings. Generally speaking the compensation works best when used under constant temperature conditions
4. Duration of measurement – Short Term vs. Long Term
   • An important consideration in picking the right load cells is to understand the stability of a load cell under short term vs. long term test conditions
   • Most scales work under the scenario where someone “
   • ” the load cell and then takes a reading. Accuracies are generally very high for these applications especially under room temperature conditions
   • But when temperatures are changing or when a constant load is placed on a load cell for a long time, and one cannot “Tare” the reading periodically there could be drift or Creep in the baseline reading. If your application cannot tolerate this kind of drift then you need to purchase a load cell with good long term stability and low creep
   • Process control applications that cannot be periodically tares and still require very high resolutions and accuracy with temperature over long periods of time – are some of the most demanding applications to outfit with a load cell
5. Data Update Rate
   • How fast do you need the reading to be? 1 Hz, 10 Hz, 100 Hz or faster?
   • This is important to know because load cells are generally speaking "quasi static" devices. That is they are not meant to measure the dynamic forces acting on the sensor - rather just the static loads
   • When you need to measure forces at a very high frequency to study the dynamics of a system - you need to purchase a force sensor with those characteristics
   • The response time of a load cell is generally of the order of 3-5 milliseconds - BUT this does not take in to consideration the mass of the body attached to the load cell. Depending on what is attached to the load cell - the response time could be much slower than what you expect
   • Furthermore, the response time is generally indicated as that of the load cells' analog output - and not that of the complete digitized system. You need to consider the data rate of the data acquisition system, the PC or PLC being used etc. to get very high data rates
6. Direction of loading
   • Load cells generally are designed for measurement in one direction - either in Tension or in Compression
   • The reason for this is that -calibration systems and calibration processes are designed for one direction.
   • If your application needs forces to be measured in both directions i.e. Universal loads - then the accuracy of the system may be lower than it is in just one direction.
   • Some load cells such as the S-Beam load cells are better for such universal applications and if your application permits the special mechanical configuration of the S-Beam load cell - then you should consider using that kind
   • Manufacturers of load cells may charge you an extra fee for calibrating the load cells in both directions
7. Mounting Options
   • This may be one of the most often overlooked aspect of load cells! Designers, engineers or users often pick a load cell and then discover they have to spend hundreds of dollars more to design fixtures or other accessories to actually use it in practice!
   • Pay special attention to the mounting options offered by load cells on the top as well as bottom of the load cell. Threaded holes are easier to work with and are generally lower in profile and less expensive to use than if you have to drill a hole and thread it on your end!
   • Also pay special attention to off-center loading conditions when you design your application. Some load cells such as pancake, button style and other circular load cells are more accurate when used axially along the center of the load cells. When off center loading conditions exist - then certain load cells such as cantilevered single point load cells offer better performance than others.
8. Output Required (Analog or Digital)
   • This is one of the most important factors to consider when picking a load cell since the type of output you want for your application is one of the biggest determining factors in the final cost of your solution
   • The most common output available from conventional load cells is mV/V. When you apply 10V DC power - you get about 20 milliVolt for full scale outputs. This is a low level analog signal which cannot be input into general purpose DAQs or PLCs and requires amplification before it can be used in that mode. Look for load cells with amplified outputs to reduce the headache associated with this step and the additional cost incurred
   • If the distance between the load cell and the DAQ/PLC is large - you may need to use the 4-20 mA type of analog output.
   • Better still - if your application works with a PC or a DAQ/PLC with digital inputs then look for load cells with Serial/RS-232/RS-485/USB or Wireless outputs
9. Total cost of Ownership
   • The cost of the solution depends on many factors:
     • Cost of load cell
     • Cost of signal conditioning equipment needed
     • Cost of digitizers/control systems
     • Cost of Programming or applying calibration to get readings in lb/Kg/N
     • Cost of periodic recalibration
   • You need to consider the total cost of solution before making a decision about which load cell to purchase
   • In addition, there could be significant unit to unit variation in performance and accuracy - so you need to consider the cost of calibrating the system - if you are an OEM designing a system to be used by an average consumer
10. Certifications Needed
    • If your application is going to be used commercially to transact business on the basis of weight, there are rules and regulations that you'll need to follow
    • For example if you are selling coffee beans packaged in 1lb bags, then you need to use NTEP certified load cells for measuring the coffee bags during packaging
    • In Europe and other areas this certification is called "OIML".
    • In general R&D, Education and Test and measurement applications do not require such NTEP/OIML certifications, but there might be industry guidelines and recommendations you need follow

Source: http://www.loadstarsensors.com/
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Digital Weigh Scale types

Weighing scales can be broadly classified into-

1. fixed
2. portable

Fixed scales can be classified as below-

Fixed Type	Description	Weight Range
Dormant scale	This scale is fixed in a pit such that it's top surface is in level with the floor. Heavy objects like cylinders/barrels can be rolled on to the scale for easy weighing. Dormant scales are commonly used in gas-filling areas to monitor cylinder weight. Filling takes place with the cylinder placed on the scale. On reaching the limit filling is cut-off or an alarm is sounded to alert the operator.	100kg to 10000kg
Tank/Hopper/Silo weighing system	Weighing system is built into the structure of the tank support. Load cells are positioned to take the tank/hopper/silo's weights. This system helps monitor/control material stock/movement.	500kg to 20000kg
Conveyor weighing system	A conveyor weighing system measures rate of flow of material- tonnes per hour (TPH). It is commonly used in industries such as mining, cement, fertilizer, etc. Load cells are fixed into under the conveyor belt which senses the weight at that point. The system includes other components like proximity switch to monitor speed. A special digitizer calculates TPH using input from load cells and proximity switch. Conveyor weighing system helps monitor/control rate of flow of material which is a critical parameter in process industries.
Crane weighing system	A weighing system is built into the structure of the crane. Load cells are positioned to measure the load lifted by the crane. This system helps avoid overloading. It is also used to monitor/control material stock/movement.	500kg to 20000kg
Filling/Packing system	A Packing/Filling system is commonly used in industries liquid or solid material are packed in containers like plastic bags, cardboard cartons, cans, bottles, etc. The system measures and fills the container with the specified quantity. Load cells installed in the system are connected to a special purpose digitizer cum controller which monitors & controls material feeders. Packing/Filling systems are common in food, sugar, cement, fertilizer, etc.	200g to 50kg
Check weighing system	A check weighing system is commonly used in industries where material (liquid or solid) is packed in containers like plastic bags, cardboard cartons, cans, bottles, etc. Check weighers are used to ensure that material quantity is right- not less or not more. The system alerts the operator whenever a package falls outside the specified limits. Some systems automatically send non-qualifying packages to reject bin. Check weighers are normally built into the conveyor system on which packed material move. Load cells installed in the system are connected to a special purpose digitizer which monitors weight data of every package moving over the conveyor.	50g to 200kg
Weigh bridge	Also called truck scales, these scales are used to weigh commercial vehicles like trucks and trailers. Weigh bridges are a must for medium and large manufacturing industries.	20T to 100T
On-board truck scale	Load cells are mounted on the truck chassis and connected to digitizer in the driver's console. This system measures the weight of the material in the truck/tipper. Onboard weighing is used as a safety feature or to track material movement continuously.	10T to 200T
Rail weighing system	Rails are modified to accommodate strain gauges and hence work as load cells. Such rails, installed in the tracks and connected to a digitizer, help measure railcar weight. The train need not stop for the measurement- weighing is done in-motion.	100T to 500T
Off-Road Truck Scales	These scales are heavier versions on truck scales. Heavy tippers used coal/iron ore mines use such scales to track material movement.	50T to 500T
Weigh-in-motion system	These systems are used to check overloading of commercial vehicles on highways. A weigh bridge positioned under the surface of the road measures the weight of truck/trailers while the vehicles are in motion.	100T

Portable scales can be classified as below-

Portable Type	Description	Weight Range
Laboratory scale	Laboratory scales are made for high accuracy-high precision measurement of light objects weighing few grams. These scales are delicate & sensitive and need to be handled with extreme care. Most cases these scales are placed in a special enclosure to protect the scale from dust, moisture and even blowing air. Test weights or objects to be weighed are handled with forceps, not with bare fingers.	10g to 1kg
Human scales	Human scales designed for home/clincal use are generally low accuracy scales. Compact floor models are the most commonly ones used to weigh human beings other than infants. There are other special types for the disabled- wheel chair scales or scale mounted stretchers. To weigh infants and small kids, baby scales are employed by hospitals.	200kg
Table top scale	Table top scales are used for weighing light weight objects. Retail stores is the biggest market for these scales. Dealers offer various models- low-cost to high precision/high accuracy models. These scales are easy to use and easy to maintain but delicate and need to be handled with care.	10kg to 30kg
Bench scale	Bench scales are low capacity scales mainly used at a retail stores. Most scales are simple low-cost, easy to use, easy to maintain devices which can be purchased of the shelf.	30kg to 50kg
Platform scale	Platform scales are available in low to high capacities having a wide range of applications right from a retail store to a warehouse to a manufacturing setup. While lower capacity scales have one load cells, higher capacity scales come with four load cells. Scale manufacturers/dealers offer simple low-cost models to expensive custom-built models with extended features like connectivity to PC or ticket-printing facility.	100kg to 500kg
Floor scale	Floor scales are designed for heavy-duty usage in industrial, manufacturing or warehouse setting. These scales usually have a two steel frames- lower and upper- between which four load cells positioned. Objects to be weighed are placed on the top deck plate which is fastened to the top frame. Load cells are connected to a digitizer via a junction box. Digitizer can be a simple weight indicator or possess advance features to transfer weight data to a PC where data is captured & stored for further use like generating reports on material movement.	200kg to 1000kg
Pallet weighing scale	Pallet Weighing Systems (PWS) helps weigh load on the spot or as it is being handled. PWS are commonly used in manufacturing setups to track material movement. Load cells and necessary accessories are integrated into the pallet truck frame so that load cells sense the weight of the material handled. A battery powered digitizer powers the load cells and displays weight on a ergonomically positioned display.	500kg to 2000kg
Hook Scale	Hook scales is a compact device with a tensile load cell and digitizer components housed in special enclosure. The load cell has hooks fixed on both ends- upper hook for hanging the scale and lower for hanging the object to be weighed. Hook scales are commonly used in cranes in loading area so that weight of the material can be checked. They are also used in production area to ascertain weights of various objects. They can also be used as safety equipment in cranes while hoisting delicate or sensitive items.	500kg to 2000kg
Livestock scale	Livestock scales or cattle scales are commonly used on farms to weigh animals. These scales are designed to accommodate the animals and coated with special paints or coatings to resist corrosive properties of animals wastes. Livestock scales are easy to carry, setup and use.	100kg to 500kg
Ramp-End Scale	Weigh pads or Portable Ramp-end Scales help weighing vehicles on any level surface. Weigh pads are used to check weight distribution on wheels/axles. These light weight and low profile scales can be carried around in a car or a van. Setting up the scales is simple- just position scales to match axle width & wheel base and connect to digitizer. The battery powered digitizer powers the weigh pads and displays weight- individual wheel weight, weight on each axle or total weight. Portable Ramp-end Scales are useful to vehicle manufacturers, car racing teams, fleet owners and highway authorities (to check overloading of vehicles).	5T to 10T
Aircraft weighing system	Aircraft weighing systems are similar to Portable Ramp-end Scales. AWS is used to check weight distribution on the wheels and also to measure total weight of the aircraft. These light weight and low profile scales can be carried around and set-up easily. Normally the aircraft to be weighed is jacked up, weigh pads positioned under the aircraft and then lowered down so that it rests on the weigh pads. A battery powered digitizer powers the weigh pads and displays weight- weight on each of the pads and also the total weight. AWS are useful to aircraft manufacturers and aircraft maintenance companies.	2T to 10T

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