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Belt Weigher Maintenance procedure
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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
no adj0.08%0.09151.31151.22
No span adjustment was made to 6A.
no adj0.05%0.07154.27154.34
no adj0.03%0.04147.43147.47
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!