Weighing System.PPT

8/18/2019 Weighing System.PPT

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Electrical Section Training 112.04.16

• Welcome toWelcome to


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212.04.16

Scales

• Scales are gravimetric devices.• In other words, they are devices that measure

the force that gravity exerts on mass.• Scales can be classified as two types:

– Differential weighing devices – Integral weighing devices


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Differential Weighing Devices

• Differential weighing devices are the mostcommon.

• You begin at one weight on a scale and thenadd or subtract weight to give you thedifference between the beginning and endingreading.


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• truc! scale starts at one reading, generally"ero, and then goes to a different weightreading when you drive a truc! onto the scale

platform.• #he difference between the two readings is the

weight of the truc!.• #ruc! scales, rail scales, platform scales,

pac!age scales, postal scales, counting scales,etc. all operate on this principle.


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• $atching scales weigh ingredients into a weighhopper on a differential basis, one ingredient at atime.

• $ul! weighers weigh and dump into and out of abul! material weigh hopper to record the highweight, the low weight, and the difference which isthe total weight transferred of bul! materials.

• %oss&in&weight feeders use a feeding device toempty a weigh hopper at a controlled rate using therate of change of weight 'the differential weightchange( as the measuring element.


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Integrating Weighing Devices

• Integrating weighing devices are the second category ofscales.

• )onveyor belt scales are integrating weighing devicesthat use a simple integral calculus summation processto measure a conveyed *uantity of material.

• #wo variables are involved: – weight and speed.

• A weight function measures the weight of a small section ofa con e!or.

• The gross weight on the scale is the weight of the "elt# the"elt con e!or i$ler an$ the material on the "elt.

• The net weight of material onl! is the gross weight less theweight of the su%%orte$ section of the "elt an$ the scalei$ler.


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• #he speed function is the second variable to be measured.• +ost modern speed sensors are rotary digital pulse

generators. #hese can be optical, magnetic or other on offsensing units. #hey are mounted on a pulley or wheel that

rotates as the belt moves. #hey generate an on off signalas they move which is directly proportional to the distancethe belt moves and the speed of the belt.


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Formulas used for commonly displayed Data:

Total weight = Weight / unit distance x distanceRate = Change of total weight / Time

Belt Speed = Distance / Time


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#ypes of $elt Scale Weighing #echnologies

• +any different types of weighing technologies havebeen used over the years for conveyor belt scales.

• #he first belt scales used mechanical integrators.

– #he speed of the belt drives a dis!. ball or another dis!rolls on this dis! at right angles to the speed dis!. #heposition of the ball or second dis! is controlled by theweight on the scale. If the ball is in the center of the speeddis!, it does not rotate at all. s the ball is moved to theoutside, it rotates faster and faster. #he speed of the ballis a mechanical multiple of the speed of dis! and theposition of the ball on the dis!. #he ball is connected to ashaft that drives a totali"er. #he speed of this shaft is therate.


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• nother method of determining the load on aconveyor belt was to use a nuclear source onone side of the belt and a detector on the other

side. – #he more material that is on the belt, the less

radiation is detected. You get an inverselyproportional signal of absorbing mass on the

belt. -sing this along with belt speed you couldma!e a belt scale. #hese were never very widespread in actual use.




• % D#/s 'linear variable differential transformers(are position sensing devices that have been usedin con0unction with spring mechanisms to measurebelt weight. – #hey are non&contacting sensors and generally have

spring mechanisms that are rugged in nature whichgives them very good overload characteristics. 1nthe down side, they can exhibit problems withthermal effects on the mechanical springs. #heseeffects can be both on "ero because of thermalexpansion and on the span due to modulus ofelasticity changes.




• Strain gage load cells are commonly used in scalestoday. – +any have been adapted to mechanical lever scales

using a lever system to sum forces at a single pointwhere a load cell is used to read the resultant forceelectronically at this point. #hese scales werecommon for retrofit installations on truc! scales forexample. lso, strain gage load cells were initiallyvery expensive and limited to in&line tension andcompression forces. #his made mechanical hybridload cell mechanisms popular. Some belt scales aremade with this technology today, but their use isdeclining.




• #oday, most scales are full strain gage suspensiontypes. #hey use little or no mechanical mechanismsand the load platform is directly supported by the

load cell system. – +ost new conveyor belt scales use this technology.1verload stops are built into the load cell mountingsystems to ma!e them rugged and reliable. lso, theyare simple in their overall design. Single point

suspension load cell designs allow for off&centerloading. #his also compensates for any extraneousside loading that could effect the true weightcomponent of the belt load forces that we aremeasuring.


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• #here are advantages and disadvantages whenconsidering conveyor belt scales. – s an integrating device, a conveyor belt scale is a

very compact device that fits into a conveyingsystem. #he scale handles large *uantities of rawmaterials on a continuous basis. It does not re*uirelarge batch hoppers, truc! scales or rail scales. Itcan handle rates that ma!e the application of

differential scales almost impractical. %oading andunloading ships is one example.


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• $elt scales have their wea! points. – 2irst, belt scales can run for extended periods of time without

returning to "ero. – #his means that any buildup on the scale that affects the "ero

will not be detected until the scale is run empty. –

"ero error is not a one&time error. #his error is continuouslyadded along with the weight of actual material. – lso, extraneous forces such as wind loading, changing belt

tension, excessive vibration, and mechanical interference withthe scale can cause errors in the weighing system.

– #he scale does not !now the difference between the forces fromactual material we are trying to weigh and the forces from

external noise. – lthough this is true of all scales, the ratio of signal to noise ismuch better on differential weighing devices than on integratingdevices. Integrating belt scales are weighing a small portion ofweight on a continuous basis and external noise can besignificant. )are must be ta!en to correctly install a belt scaleand to protect it from external influences


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2ree 2all $ul! 2low +eter

• During 3free fall3, a non&contacting mass flowmeasurement can be performed at the delivery endof conveyor systems such as vibrating conveyors,

screw conveyors, rotary dischargers, chainconveyors and conveyor belts. #he material isirradiated during its 3free fall3 to determine theweight per area.

• #he material flow in tons hour is calculated fromthe product of weight per area and material speed.


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Electrical Section Training 1&12.04.16

%oss&in&Weight 2eeder for highly precise, continuous processes%oss&in&Weight 2eeder for highly precise, continuous processes

%oss&in&Weight 2eeders are continuously weightcontrolled hopper combined with a volumetric feeder.#hey generate a controlled, absolutely constant mass

flow, as re*uired in mixing processes, for example.

2or the refill of the weigh feeders & co&ordinatedsystems feeder such as pneumatic conveyors or

volumetric feeders.


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Electrical Section Training 1'12.04.16

$asic 1perating 4rinciple of weighing

• Weighing instrument – measuring instrument

that serves to determinethe mass of a load byusing the action ofgravity.

– ccording to its methodof operation, a weighinginstrument is classifiedas automatic or non&automatic.


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Electrical Section Training 1(12.04.16


• utomatic weighing instrument – n instrument that weighs without the intervention of

an operator and follows a predetermined program ofautomatic processes characteristic of the instrument.


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• )ontrol method – #he method used to determine the mass of the

product used as the test load during material

tests. #his will generally involve the use of aweighing instrument, referred to as the controlinstrument.


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• )ontrol method – #he method used to determine the mass of the

product used as the test load during material

tests. #his will generally involve the use of aweighing instrument, referred to as the controlinstrument.


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•)ontrol metho$


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Weigh 2eeder5


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#ypes of weighing system


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#ypes of weighing control system


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1verview 2eeding1verview 2eeding

6.6. olumetric 2eedersolumetric 2eeders

7.7. 8ravimetric 2eeders8ravimetric 2eeders


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IncreasingIncreasingaccuracyaccuracy

6. olumetric 2eeders

• 9igh accuracy feeder

• Screw

• $elt feeder

• otary value

• $in Discharger

• 8ravity feeder


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$ase for efficient and accurate feeding

carefully designed volumetric feederwith agitator, homogeniser and largeentry section to ensure:

a continuous product flow

and

a constant bul! density


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1ther influences:• *ariation of the "ul+ $ensit!• ,on-constant filling $egree of

the screw

$ul! densitychanges in functionof the product level

'head effect(( = f (h ))

%imits of the volumetric feeding

1 > 2 > 3

%9

%%

3

2

1


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Agitator- ri e /nlet

*ent S%igot

o%%er

Agitator

2eeder 8%D ABScrew- ri e /

ntromitter- ri e /ntromitter

ee$ing Tu"eScrew eli

utlet Tu"e

obust, precise volumetric feeder layout is mandatoryfor an advanced volumetric feeder

C8eared ) motors


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7. 8ravimetric 2eeder 8ravimetric 2eeder

9igh precision, robust,9igh precision, robust,reliable and durable constructionreliable and durable construction

were the main ob0ectives for thewere the main ob0ectives for thedevelopment of the 8eric!edevelopment of the 8eric!egravimetric 2eeders DIW& E, F=,gravimetric 2eeders DIW& E, F=,

7== and DIW&E7== and DIW&E


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4rinciple of continuous gravimetric feeders

t m m const.

efilling capacityapprox. 6= x feeding capacity

'0

20

fre*uencyinverter

refilling valve

load cell

rpm

feed rate

controlvalue

external setpoint


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#are&compensated mechanic allows the use of heavy duty)&Drives and gearboxes in a weight feeder 'no #ara weight(

olumetricfeeder

2orce transmissionspring

+echanicaloverloadprotection

#are&compensating&

spring

1il damper

4arallelogramweighing frame

%oad cell

G 1nly the bul! materialinside the feeder H hopper ismeasured by the load cell

ibrations and disturbancesare +E)9 ;I) %%Y damped$E21 E they reach the load cellor the E SYD1S controller input


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E SYD1S 4lug H Dose

4re&wired and ready to start• +otor • 2re*uency converter • %oad cell• egulator • )ontractors

• #erminal strips• Input 1utput

terminal


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E SYD1S )ontroller 9ighlights

• 1nly one standard load cell, which is mechanically protectedagainst destruction 'overload( and vibration 'oil damper(

• Stand alone system. 1peration and display on the scale asstandard e*uipment. ;o additional service panel or controlsystem re*uired

• 9igh accuracy achieved by #rend#ech feedrate calculationalgorithm.• utomatic calculation of bul! density and head effect

compensation. ;o additional actions or inputs necessary.• Self optimising feeding by permanently updated profiles, F=

different products with separate profiles

• Easy operating. E SYD1S&)ontroller menus available inEnglish, 2rench, 8erman, Spanish, Italian, Dutch• Easy lin!ed to common field busses such as:

+od$us, 4rofi$us D4, Device ;et, Ethernet etc.• Executions for #EJ Kone 6, 7, 76, 77 available


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$elt weigher

$elt weighers permit a continuous weighing of bul!materials. #he bul! material running over the belt isweighed on a defined measuring section. In the

controller the feed rate is then calculated andregulated. In feeding mode the belt speed regulatedto provide consistent feed rate. In measuring modethe belt speed is constant and the mass flow is

measured. #he accuracy particularly depends on thecalm tape operation and on as consistent materialallocation as possible.


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$elt weigher

2re*uency&Inverter

)4-

E SYD1S E$&6

+

-

+easuring section

7

+otor speed

ctual&

value

Setpoint


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Electrical Section Training 3(12.04.16

Differences between $atch and loss&in&weight

E$&6 $atch controller • Small *uantities can be dosed

e.g. 6== g from 7= !g balance• If there is not enough product

in the hopper it is refilled first&> no continuous mass flow• olumetric mass flow 'fast and

tric!le speed(• -p to 6L ingredients, MM

recipes, two se*uences• 2ast and tric!le speed• Interruption and continuation

of the batches possible .

E%&6 loss&in&weight controller • $atch si"e min. 7= ? of the

max. scale weight,recommended proportion max.scale weight min. feedrate

max. 6:6=• 2eeding during the refill & > no&

brea! 6=== !g batches with a7= !g balance possible

• )ontrolled mass flow•

1ne ingredient• ;o tric!le speed• 1nly abort of the $atches

possible


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t

mll have to be the same

ccuracy of continuous feeding

9ow is the regularity of a continuous mass flowto be determined5

t

m

2eeding time t

W e i g h t m

t

m


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Weighing System.PPT

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