Conveyor Belt Scale

Maintenance

Care and Feeding Instructions

Fundamentals:

� What is a conveyor belt scale ?

� What can I do with it ?

� What I shouldn’t do with it ?

� How does it work ?

What is a Conveyor Belt Scale ?

A device that incrementally

measures and totalizes a

continuous flow of bulk

material moving on a

conveyor.

( A gizmo that weighs the

stuff on the belt every couple

of inches as it goes from

here to over there )

What can I do with it ?

A conveyor belt scale can be an accurate

means of inventory control and process

control.

( It will tell me how much I have, and let me

know if I am putting enough of it where it

belongs. )

Inventory Control

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No span adjustment was made to 6A.

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Action% ErrWt. ErrTruck Wts.Belt Wts.

Material Test Results

6Aproject:

6/19/2001Material test

Process Control

What I shouldn’t do with it ?

A conveyor belt scale is not accurate at measuring fluid material, small discrete weights, or material traveling vertically.

( Don’t weigh water, individual diamonds, or stuff that is falling )

How does it work ?

� Rate = Weight x Speed

� Total = fWeight x Speed DTime

How does it work ?

� Speed Signal = A frequency signal proportional to belt travel.

( As the belt moves every couple of inches, the speed sensor gives a pulse.

How does it work ?

� Weight Signal = A voltage signal proportional to force.

( As weight is applied to the scale carriage, the output from the loadcell increases )

Technical Stuff

� Loadcells 101

( everything you ever wanted to know about a loadcell,

that you were afraid to ask )

Strain Gauges

The Wheatstone Bridge

Sensing Weight

Almost Sensing Weight

� Deflection , Side Loading and Binding

Weighing with Idlers

� Weighing on an Incline

� Weighing through a conveyor belt

� Idler Spacing

Weighing through a conveyor belt

� The troughing angle

The higher the angle, the rigidity

of the belting increases.

� Belting construction

Size does matter!

Thinner is better.

Idler Spacing

� The idler supports the belt half the distance from the

previous idler to half the distance to the following

idler.

Material Speed

� We can measure the belt speed, but what we really

need to know the material speed.

Sensing Speed

� The speed signal is just

as important as the

weight.

� A 1% error in the speed

input will cause a 1%

error in the scale

output.

Conveyor Properties

� Belt Tension

� Belt Tracking

� Idler Alignment

� Side Loading

Belt Tension

� Things that mess up the tension

� Applying load

� Letting the belt track into the structure (drag)

� Curves in the conveyor

� Tracking the belt to run in a straight line

� Running the motor

Belt Tension

Belt Tension

� Things that help keep tension consistent

� Gravity Take Ups

� Good belt tracking

� Good Idler Alignment

� Location of the scale

Idler Alignment

� Allows for best transfer of weight through the

conveyor belt.

How do we know if it is right?

� Test it, compare it, run it fast, run it slow, and

then test it again!

( If you have no way to check your scale, then I

can guarantee that the weight is close

enough. )

Material Test

� Check it against a know load.

Test Chains

Test Weights

Simulated Load

The Hard Part

� What makes it stop working ?

� What makes it work poorly ?

� What makes it work well ?

Spillage

Conveyor Maintenance

� I still haven’t figured out

why you would store the

water hoses on the

wing rolls of the scale

idlers.

What make it work well?

That’s easy

Just don’t do all the things

that make them work

poorly!