Metal Detector User Training-Part 1(Basic)

1Machine Base Training – Metal detector Part 1(Basic Theory & Principle)

NESTLE INDIA LIMITEDNESTLE INDIA LIMITED

Submitted BySubmitted ByBrijesh Pratap SinghBrijesh Pratap Singh

B.Tech(EC)-0703231035B.Tech(EC)-0703231035ABES ENGINEERING COLLEGE ;GHAZIABADABES ENGINEERING COLLEGE ;GHAZIABAD

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About Nestle India Limited Nestlé S.A.Nestlé S.A. (French pronunciation:  (French pronunciation: [[nɛsˈlenɛsˈle]]) is the largest ) is the largest

nutrition and foods company in the world,founded and nutrition and foods company in the world,founded and headquartered in headquartered in VeveyVevey, , SwitzerlandSwitzerland..

Nestlé originated in a 1905 merger of the Anglo-Swiss Milk Nestlé originated in a 1905 merger of the Anglo-Swiss Milk Company, which was established in 1866 by brothers George Company, which was established in 1866 by brothers George Page and Charles Page, and the Farine Lactée Henri Nestlé Page and Charles Page, and the Farine Lactée Henri Nestlé Company, which was founded in 1866 by Company, which was founded in 1866 by Henri NestléHenri Nestlé..

Today, the company operates in 86 countries around the world Today, the company operates in 86 countries around the world

and employs nearly 283,000 individuals.and employs nearly 283,000 individuals.

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The Company's principal activities are to manufacture The Company's principal activities are to manufacture and distribute food products. and distribute food products.

The food products include milk and nutrition, soluable The food products include milk and nutrition, soluable beverage powder, coffee blends, tea, cream, chocolate, beverage powder, coffee blends, tea, cream, chocolate, cereals and cooking aids. cereals and cooking aids.

. Milk products and nutrition accounted for 43% of . Milk products and nutrition accounted for 43% of 2001 gross revenues; soluable beverage powder, 29%; 2001 gross revenues; soluable beverage powder, 29%; prepared dishes and cooking aids, 14%; chocolate and prepared dishes and cooking aids, 14%; chocolate and confectionery, 14% and other, nominal.confectionery, 14% and other, nominal.

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Metal Detector Metal Detector Theory and Theory and

PrinciplePrinciple

5Machine Base Training – Metal detector Part 1(Basic Theory & Principle)

1.1.General General

IntroductionIntroduction

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Why need Metal Detectors ? 1. To protect our customers

• Bits of metal can be seriously dangerous if swallowedesp. baby food .

2. To protect the Company’s reputation• Deaths or injuries from swallowing metal contaminants in product, can cause

companies to go out of business or to a lesser extent, seriously damage its reputation.

3. Complying with legislation/quality control• Ensure goods produced comply with company’s agreed assured standard e.g.

HACCP programme • Complying with food’s regulation. • Legal issue

4. CP 18.271 (Guidelines for installing, evaluating and testing metal detectors) states As the total quality of our product has to be warranted, the NQS (i) states “the

presence of metal and glass fragments must be completely avoided since these foreign objects may cause injury to the customer ”

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Facts and Myths of Metal Detector1. It Can :

• Sense the presence of “metals” contaminants going through its aperture• Output a reject command (stop the line) if the measured signal exceed a set

limit (threshold) • Go or No Go ( Policeman, speed limit)

2. It Cannot :• Detect plastics, woods, paper etc..• Indicate the material (brass, iron Etc..) of the contaminants• Detect contaminants sizes below the specification value• Measure the size of contaminants

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OverviewOverview •Detector - picks up a signal•Electronics - compare signal against set-point (Threshold)•If Signal > Threshold Metal Strike Alarm

Electronics

Detector

A. Metal contaminants•Sizes/shape•Material

B.Product•Moisture•Lumpy/undried•Recipe-mineral•Free-fall

C.Installation•Vibration/Clearance•EMI/RFI•Metal free zone•Static•Earthing

E.Detector•Position/Orientation•Aperture Size•Frequency•Head power

D.Electronics•Threshold•Stability-ABC•Signal processing•Phase control•Calibration

What can cause a signal?

Most of the false strikes arise from B and C

False strikeUnstable operation

False strikeLet throughUnreliable operation

Only wantOnly wantTHIS THIS

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Physics Principles of Metal Detection

Michael Faraday 1791-1867

Faraday’s Law of Electromagnetic induction

(1831)

When a magnet is moved through a closed coil of wire, a current is induced in the wire. The direction of the current flow is such as to create a magnetic field opposite in direction to that of the change in the field produced by the magnet…..

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Initial application for metal detectionMarine engineers utilised Faraday’s technology, fitting wires around the hulls of ships and attempted to detect large masses of metal around and below them, e.g. Submarines, wrecks & mines

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How it started in the food industry 1950’s - Food companies wanted to check for metal in 1950’s - Food companies wanted to check for metal in

the product that they produced. Principally looking for the product that they produced. Principally looking for nuts and bolts that came from their manufacturing nuts and bolts that came from their manufacturing process.process.

1972 - A person attempted to extort money from a baby 1972 - A person attempted to extort money from a baby food manufacturing company, by putting hypodermic food manufacturing company, by putting hypodermic needles into their product. The worlds press published needles into their product. The worlds press published the story, there was then an urgent need for all food the story, there was then an urgent need for all food companies to metal detect their products. companies to metal detect their products.

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2.2.Construction Construction

of of Metal DetectorMetal Detector

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General Anatomy - External

End Plate

Aperture

Stainless Steel Case Touch Panel

Aperture Lining

IP 67 or Nema 4XElectronic Controls

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The casing is filled with a glass bead and resin potting for stability

Transmitter Coil in the center of the wire former

Wire Former

Receiver Coils on the outside of the wire former

General Anatomy - InternalGeneral Anatomy - Internal

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Glass bead & Resin

Folded Stainless Steel case

Wire Former

Receiver Coils

Transmitter

General Anatomy - Cross-Section View

Flexible Silicon Aperture Lining

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3.3.Principles Principles

of of DetectionDetection

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Principles of Metal Detection -"Coupling"

The magnetic fieldThe magnetic fieldcreated by the oscillator created by the oscillator in the transmitter coilin the transmitter coilresults in "Coupling"results in "Coupling"between the Transmitterbetween the Transmitterand each of the Receiverand each of the ReceiverCoils.Coils.

A voltage is thusA voltage is thus"Induced" in each of the"Induced" in each of theReceiver Coils. Receiver Coils.

Receiver Coils

MagneticField

Transmitter Coil (Oscillator)

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Signal

0V-OUT = 0

MetalMetal

Signal output – metal contaminant

V- OUT

RX-1

RX-2

TX

Input to TX is an

Oscillator from 8v

to 30v Peak-

Peak,

50Khz to

1000Khz

When a metal piece enters the detector, this balanced condition is disturbed and the detection signal V-OUT will have a value.If this is more than a preset value (Threshold) it will be interpreted as a metal

MetalMetalMetal MetalMetalMetalMetalMetalMetalMetalMetalSignal

0

Time 0Time 1Time 2Time 3Time 4Time 5Time 6Time 7Time 8Time 9Time 10Time 11Time 12Time 13Time 14Time 15Time 16Time 17Time 18Time 19Time 20

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4.4.Factors Factors

influencing influencing SensitivitySensitivity

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4.14.1Metal TypesMetal Types

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Metals are classified into 3 categoriesMetals are classified into 3 categories The ease of detection depend on 2 key properties of metal i.e.The ease of detection depend on 2 key properties of metal i.e.

a.a. Magnetic permeability (how easily they are magnetized) and Magnetic permeability (how easily they are magnetized) and b.b. Electrical conductivity.Electrical conductivity.For metal detection the For metal detection the magnetic propertymagnetic property is is dominantdominant..

FerrousFerrous Ferrous contamination is both magnetic and a good electrical conductor and Ferrous contamination is both magnetic and a good electrical conductor and

is easily detected. Most metal detectors are able to detect small ferrous is easily detected. Most metal detectors are able to detect small ferrous particles. particles.

Non-FerrousNon-Ferrous Non-ferrous metals such as copper, lead and aluminum, are non-magnetic but Non-ferrous metals such as copper, lead and aluminum, are non-magnetic but

are good electrical conductors and are generally quite easy to detect.are good electrical conductors and are generally quite easy to detect.

Stainless SteelStainless Steel Stainless steel comes in many different grades, some magnetic and some Stainless steel comes in many different grades, some magnetic and some

austenitic ( totally non-magnetic ) and their conductivity is variable. austenitic ( totally non-magnetic ) and their conductivity is variable. Generally most difficult to detect compared to ferrous and non-ferrous.Generally most difficult to detect compared to ferrous and non-ferrous.

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How is ferrous metal detected?How is ferrous metal detected?Receiver Coil

CauseA ferrous (Magnetic) material, enters the head and moves through the magnetic field

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How is ferrous metal detected?Receiver Coil

Effect

This will improve the magnetic coupling in the area and increase the output of the receiver coil

CauseThe magnetic field, will be strengthen as the ferrous metal enters the field

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How is non-ferrous metal detected?How is non-ferrous metal detected?Receiver Coil

CauseA non-ferrous (non-magnetic)

material, enters the head and moves through the magnetic field

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How is non-ferrous metal detected?How is non-ferrous metal detected?

Cause•The non-ferrous metal will create a secondary magnetic around itself•This field is in opposition to the main magnetic field•Net effect will weaken the main field

EffectThis will reduce the coupling in that area, and decrease the output of the receiver coil affected by the coupling in that area.

Receiver Coil

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4.24.2OrientationOrientation

EffectEffect

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Orientation Effect – Ferrous metal AA FerrousFerrous segment segment

of wire will be of wire will be easiesteasiest to detect to detect when presented when presented with its longest with its longest dimension in the dimension in the horizontal axis. horizontal axis.

A A FerrousFerrous segment of wire segment of wire is is most difficultmost difficult to detect when it to detect when it is presented with is presented with its longest its longest dimension on the dimension on the vertical axis. vertical axis.

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Orientation Effect - Orientation Effect - Non-FerrousNon-Ferrous MetalMetal

A segment of A segment of Non-Non-FerrousFerrous wire is wire is easiesteasiest to detect to detect when presented when presented with its longest with its longest dimension in the dimension in the vertical axis. vertical axis.

A segment of A segment of Non-Non-FerrousFerrous wire is wire is most difficultmost difficult to to detect when it is detect when it is presented with its presented with its longest dimension longest dimension on the horizontal on the horizontal axis. axis.

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4.3 Vibration4.3 Vibration Any form of mechanical vibration to the head will disturb the magnetic field Any form of mechanical vibration to the head will disturb the magnetic field

and may cause a false triggersand may cause a false triggers

Microscopic movements of the coils relative to each other, as small as 1 Microscopic movements of the coils relative to each other, as small as 1 micron, can cause an out-of-balance voltage and a false detect signal. The micron, can cause an out-of-balance voltage and a false detect signal. The selection of former material, coil specifications and case design are crucial.selection of former material, coil specifications and case design are crucial.

Sources of vibration - motors, pulleys, auto-reject devices, temperature Sources of vibration - motors, pulleys, auto-reject devices, temperature changes, transportation and close-by machinerychanges, transportation and close-by machinery

Head must be mounted securely to permanent and rigid structureHead must be mounted securely to permanent and rigid structure

Shock absorber must be installed on the mounting. Shock absorber must be installed on the mounting. Use approved design - no through boltsUse approved design - no through bolts

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4.4 Clearance4.4 Clearance There must be sufficient clearance between the product chute There must be sufficient clearance between the product chute

and the side of the detector and they must be properly centredand the side of the detector and they must be properly centred

Any physical contacts may transfer vibration to the head Any physical contacts may transfer vibration to the head causing false triggercausing false trigger

For installations using flexible product chute, the vacuum For installations using flexible product chute, the vacuum created during product movement will cause the flexible chute created during product movement will cause the flexible chute to sometimes contract or expand resulting in occasional to sometimes contract or expand resulting in occasional physical contact with the throat, resulting in false trigger.physical contact with the throat, resulting in false trigger.

Install pressure equalising line from machine hopper to MD Install pressure equalising line from machine hopper to MD inlet pipe inlet pipe

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4.54.5ProductProductEffectEffect

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Product moisture and recipeProduct moisture and recipe Any material that is a conductor of electricity will trigger the metal Any material that is a conductor of electricity will trigger the metal

detectordetector

Product moisture is water and it is a good conductorProduct moisture is water and it is a good conductor

Undried product in lumpy/granular form may contain sufficient water Undried product in lumpy/granular form may contain sufficient water trapped within to trigger the metal detector.trapped within to trigger the metal detector.

The rejected products may test negative after a few days as the The rejected products may test negative after a few days as the particles could have been broken up or the product could have particles could have been broken up or the product could have becomes drierbecomes drier

Product with fortified iron content may also trigger the metal detectorProduct with fortified iron content may also trigger the metal detector

33Machine Base Training – Metal detector Part 1(Basic Theory & Principle)

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