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Thread: Belt Weigh Feeder Conveyor Design

  1. #1

    Belt WeighFeeder Conveyor Design

    I'm quite a beginner in bulk material weighing and now I have a project to implement bulk weighing.

    Please can anyhow explain me from where should i begin.

    I have seen a typical system that has an idler mounted on two loadcells and the output is connected to the PLC. Please give me a clear idea on the things that I should know before I begin.

    Hope you experts will somehow help me.

    Last edited by arunkish; 14th March 2008 at 15:37.

  2. belt weigher

    There are certain factors that you have to understand to find a solution for belt weighing.
    1) What is the capacity of the belt?
    2) The belt load is (belt capacity/3600)/belt speed.

    The loadcell capacity will be the belt load + the idler weight + the belt weight per meter.

    This ratio of belt load to dead load will determine the accuracy of the system.

  3. Hello,
    There are two basic variables that are needed. First is a representation of load. Usually described in lbs. per foot or Kg per meter. The other variable is belt travel in feet or meters per second. By combining both signals you can get lbs. per second or alternately kg per second. If you accumulate this combined signal based on distance travelled you can get a total weight. There are alot of influences on get both of these signals correct, and if you have any specific questions, post away! There are a number of experienced people that read this forum.

    Todd Dietrich

    Kaskaskia Valley Scale Co.

  4. #4
    Dear Friends
    Thanks everyone for posting your valuable reply. The material going to be weighed is the leaf of the tea plant.

    The maximum kg to be weighed per hour will be set by the user and the max allowed is 5000 kg / hour.

    I have planned to set the belt width to 1000 mm.

    Will I require an encoder for the calculations and what will be the formula? What kind of PLC and loadcell will be required to carry out this operation?

    Thanks & regards

  5. #5
    5 tonnes per hour on a 1m belt sounds like the belt will always outweigh the tea. You need some specialist help in calibrating that one because the dynamic disturbances from belt passage over the idlers and uplift from cross wind can cause big percentage errors with that kind of set up.

  6. Your Tea Feeder will have light loading. In other words, the change in weight from an empty belt to a loaded belt will need to be at least 10% of the load cell size. Your best bet is to have a conveyor belt speed that is very slow. Here is how the math goes.

    5000 kg /hr passing over an idler that is spaced 500 cm apart from the adjacent idlers with a belt speed of 3 meters per minute.

    5000 kg/hr = 83.33 kg / min

    83.33 kg /min travelling a 3 meter per min = 27.77 kg / meter

    27.77 kg / meter applying weight to an idler spaced at 500 cm
    would give a weight of 13.89 kg on the idler

    a 100 kg load cell would see a change of signal of about 14% at maximum capacity. Slowing the belt down increases the weight proportionally. Increasing the spacing between the idlers also increases the loading seen by the weigh idler.

    ( I did the math in feet and pounds and then coverted back to metric. As an American farmboy, I can not grasp the metric system unless forced by others.)

    Todd Dietrich

    Kaskaskia Valley Scale Co.

  7. If this is for tea, the belt has to be synthetic and the idlers have to be of low weight i.e polymer construction.
    The weighing arrangement is also crucial as the weight of the idler and belt will have to be nullified. The distance between idlers will have to be as high as possible.
    We have supplied a lot of conveyor weighing systems for tea.

    You can contact us at

  8. Tea Feeder

    Hello Mr Kurian

    I agree with Mr. Dietrich. We have often seen clients using this arrangement to perform weighing. We do recommend using in integrator and speed detector before the PLC for ease of use and ease of calibration and accuracy.
    Accurate measurement of speed is essential. If the speed is off by 1%, totalization is off by 1%, assuming you are totalizing.
    Compensating for deadload and averaging the deadload of the belt over a complete revolution is also essential. This is called tare or zero.
    It is essential that the supported idler is absolutely level with at least two idlers before and after. This is why many clients use a weighframe.
    The distance between the idlers should not be so great as to have visible sag in the belt. Absolutely sag should be no more than 4% (of the idler spacing) assuming reasonably correct tension adjustments.

    Mike Tallevi
    Mike T.

  9. Weighfeeder design for tea leaves


    A friendly suggestion weighfeeder design and construction is a specialised subject. The basics are simple - the implementation not so . One needs to consider appropriate infeed device based on material properties, extraction forces, speed reduction, drive selection , speed pickup and weight pick up arrangements, volumetric capacity needed, belt width selection, belt tensioning and tracking, quality of joint , proper algorithm for speed and belt load derivation, normalising, multiplication, scaling to get the actual feed rate, setpoint - actual comparison , a PI algorithm to generate correction signal to variable speed drive , fault alarms ----- the works! Plus the design details of proper mechanics .

    If you are an user - a better bet would be to get an experienced supplier.

    If you are a budding manufacturer - rather late in the day . The field is as it is crowded.

    Also - tea gardens are very poor in advanced maintenance staffing - and very very cost tight .

    Feel free to email me if you want more detailed info .
    Benukrishna Mandal

    Management and Engineering Advisor

    Email :

  10. #10

    Low Density Weigh Belt

    Thayer Scale manufactures weigh belts specifically designed for low loading, low density applications such as yours.

    These designs consist of a unique suspension system inter-posed between a mass counter-balanced, multi-idler weigh bridge and a single load cell.

    This system permits load cell selection based on net, rather than gross weighing requirements. The suspension system also blocks all extraneous horizontal force vectors (belt tension, friction, torsional forces, etc.) from being misinterpretted as changes in material weight.

    These products are used globally to accurately blend tobacco leaf, measure the flow of snack chips and control the flow of natural and synthetic fibers with bulk densities as low as 4 kg/cubic meter.

    Visit for additional information.
    Attached Files Attached Files

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