How Modern Day Belt Weighers Work | 2014

Basic Operation of a Belt Scale

The modern day belt weigher is known by many names.  These include belt scale, weightomoter, conveyor scale, dynamic scale and in-motion weigher.  You will also find spelling variations on these such as beltweigher and beltscale.

Today’s belt weighing sytem consists of a weighing frame, load cells, a belt speed sensor and an integrator.

The weigh frame typically is made of a short section of steel channel with cross-members and one or more sets of  rollers on idlers that are designed specially for weighing applications.   The weigh frame is inserted into a section of the conveyor that has been removed.   Modern day belt scales used in heavy industry’s such as coal, minerals and iron ore use electrical load cell technology.  A load cell essentially converts the force of the weight of the material into an electrical signal.  To compute mass flow rate the electrical signal from the load cells is combined with an electrical signal from a belt speed sensor in a device known as an Integrator.   The integrator is a PLC or micropressor and some sort of a user interface device.

Knowing the mass and the belt speed the mass flow rate can be calculated and is typically expressed in tonnes per hour or kg per metre.  Total tonnes conveyed over a given period of time can also be calculated..

There are many factors to consider when selecting a belt weigher.   There are different load cell configurations such as pivoted, counterbalanced and fully suspended.  The specifics of the application will determine what configuration is most suitable.
 

RTI Belt Weighers

RTI supply and service the Process Automation  (PA) premium quality electro-mechanical belt weighing systems primarily for the coal, iron ore and minerals industry’s.

Unlike most other systems, RTI’s belt scale range incorporates a counter-balance mechanical design which virtually eliminates measurement error inherrent in standard weighers that use a traditional pivot or fully suspended frame design.

The RTI Econoweigh®, Accuweigh® and UniPro® range of beltscales combines our counter balance engineering advantage with quality components, manufacturing excellence and practical field know-how to deliver an Australian manufactured weigher that provides unrivalled accuracy and repeatability, day to day, month to month, year to year.

 

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The RTI Counterbalance Engineering Advantage


Most conveyor belt scales utilize a fully-suspended free-floating weigh frame design.  Historically, this simple design was considered adequate.   However, modern-day bulk materials handling is all about accuracy, quality and efficiency.  Increasingly, near-enough is not good-enough.


The issue with free-floating belt weighers is the mass of the frame and associated idlers in relation to the mass of the bulk material being weighed.   When this ratio is relatively high, which is common in many coal and mineral conveyor systems, the accuracy of the scale is seriously compromised.  This is because the weight measured by the load cells is dominated by the dead weight of the weigh frame.  The RTI counter balance system removes the dead weight from the load cell by using a frictionless pivot with the weigh idler on the one side and the load cell and counter weight on the other side.  A counter balance weight is sized to match the weight of the scale weigh frame, idler and belt, which brings the arrangement into perfect balance.   The only weight measured by the load cell is therefore that of the bulk material being measured.

RTI supply the following state-of-the-art PA beltscales:
 

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Conveyor belt weigher –    Application questionaire

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