Seminar on

Metal Detectors in Food Industries

Presented By- Aman Paul M. Tech. Food Technology-Food Chain

Management Roll No.-10MTFTFC005

Presented To- Department of Food Process Engineering,

SHIATS, Allahabad (U. P.)

1

ContentsS.No. Topic Page

No.1. Acronyms 32. Objective of Seminar 43.a.b.

c.

IntroductionMetal ContaminantSources of Metal Contamination in FoodsNeed of Metal Contaminant’s Detection

566

8

4.a.

Metal Detection DevicesBasic Principle of Metal Detector

910

5.

a.b.c.d.e.

Factors Affecting Working of Metal Detector

Contaminant FactorsDetector FactorsInstallation FactorsProduct FactorsElectronic Factors

12

1315172020

6.

a.

Alignment of Metal Detector with FSMS Plan

Action in Case of Deviation

21

22

7. Limitations of Metal Detectors 238. References 24

2

Acronyms

E - Electromagnetic Force Φ - Magnetic FluxT - TimeWb - WebberSec - SecondV - VoltB - Magnetic Flux DensityA - AmpereN - Newtonm - Metera - Areaμ - Magnetic Permeabilityμo - Magnetic Permeability of Substance in Spaceμr - Relative Magnetic Permeability of Medium ρ - Resistivityσ - Conductivity

3

Objective of Seminar

1. Studying basic working principle of metal detector.

2. Observing the basic causes of false detections by metal detector.

3. How metal detectors are aligned with the HACCP program.

4

Introduction

Food technology is moving towards a new era, of food safety. With the increasing zeal of consumer towards food awareness, the safety has become the prime concern of every firm. Implementation of GMP’s and HACCP program has oriented the industry towards a new dawn. Such programs mainly emphasize on the microbial, physical and chemical safety of the processed food stuffs. With the globalization of firms, the continuous exporting and importing of food products throughout the world has become common. In such a situation food safety has become important, not only from consumer point of view but also in tagging up of the firm’s global image. International standards such as ISO 9001 and ISO 22000 aided the global standardization process.

Food safety consists of the underling of the food hazards, irradicating or reducing them to acceptance limit and further prevention. The hazards may be physical, chemical or biological. In this seminar we will mostly focus on the detection of physical hazards that can be detected on the basis of there electrical and magnetic properties, i.e. we will talk about the detection of metallic particles in food processing industry.

5

Metal Contaminants

Metal contaminants are physical hazards that could cause serious internal damages to the body when accidentally consumed. A particle of size greater than 2mm can cut all the way when it enters the mouth, proceeding from throat to stomach and so on. These cuts cause internal bleeding and even death. They can enter through various sources in the food.

Sources of Metal Contamination in Food

There are many channels the metal contaminants can follow to enter the food. Few of them are listed below:-

1. Raw Material- The raw material can itself be contaminated at the primal level. The contaminants can enter the chain while the processes of harvesting, threshing, drying, storing, etc. are being carried out. Talking about the Indian scenario, there are no check points in the farms as such. This makes the post harvest activities of raw material really prone to metallic contamination.

6

2. Transportation- Fresh produce of fruits and vegetables are usually transported in crates which may be open and exposed to the environment to facilitate metabolic activities, this increases the risk of metallic contamination in the food.

3. Processing- During processing the metal contamination can occur through processing equipments, exposed lines, etc. The food contact surfaces of the equipments may serve as a source of metal inoculation in the food product.

4. Packaging- Packaging infrastructure is a complex unit in itself, which has many potential areas where metal contamination can occur. For example, any screw can fall from the equipment into the product. This is the most common source of contamination from the packaging unit, as the machine is continuously vibrating so there are chances that any of the screw loosen up and contaminate food.

7

Need of Metal Contaminant’s Detection

The following reasons necessite the need of metal detection:-

1. Social Responsibility- As we have seen in the above article that the metal contaminants when consumed can even cause death. So it is a social responsibility of every food technologists to exclude all such contaminations for humanity.

2. Consumer Safety- Consumer is investing his trust in the company by buying the product, and if his trust is lost it will let him move towards jurisdiction.

3. Firm’s Image- Global players often loose there image if they encounter any food safety remarks on there brand, these could even uproot there international brand image.

8

Metal Detection Devices

The most commonly used metal detection devices are:-

1. Sifters2. Metal Detectors3. X-rays

Sifters are used to eliminate particles of size either greater than or smaller than that of food. But sifters are ineffective when the contaminations are inside the food stuff. This makes there use very rare in the industry. X-rays have now become old fashioned. As the debate regarding exposure of food to irradiation is still incomplete and safety concern of food irradiations are highlighted the X-rays have departed there way out of the food industry as a potential metal detection device. Metal detectors working on the electromagnetic principle have now replaced sifters and X-ray utilizing devices. These metal detectors have now become the soul of every Food Safety Management System (FSMS). Now lets see how these metal detectors really function and the factors affecting there working.

9

Basic Principle of Metal Detector

1. Metal detector works on the “Faraday’s Law of Electromagnetic Induction”. According to this law “whenever the magnetic flux linked with an electric circuit is altered and electromagnetic force is induced in the circuit”.

E = - dΦ/dT Unit of E = Wb/Sec (Volts)

Here the Magnetic Flux (Φ) is the magnetic lines passing through a given area.

Φ = B.a.cosϴ

Where “ϴ” is the angle between a normal area “a” and direction of B.

2. Construction- The basic construction of a metal detector is shown below.

10

Transmitting coilTx(One)

Receiving coilRx(Two)

Metal Strike Zone

The transmitting coil generates a high frequency magnetic field, while the two receiving coils pick up the oscillating field. The receiving coils are connected to display and alarm.

3. Schematic Block Diagram

4. Functioninga. In a normal state magnetic field coupled is

equally to both coils. Therefore a balanced condition exists so no signal is generated on display.

b. When the contaminant enters, it distorts the magnetic field, which upsets the balanced condition and a signal is detected, which is displayed on the display-screen connected to the receiving coil.

c. This signal is compared to the threshold, if it is above the threshold, the alarm rings.

11

Signal Generation

Comparison with

Threshold

Alarm if Signal

>Threshold

Display Signals

Factors Affecting Working of Metal Detector

The following factors affect the working of metal detector devices:-

1). Contaminant Factorsa. Materialb. Size and Shape

2). Product Factorsa. Moistureb. Undried/Lumpyc. Recipe (Minerals)

3). Installation Factorsa. Vibrationb. Clearancec. EM/RF Interferencesd. Metal Free Zonee. Earthing

4). Electronic Factorsa. Thresholdb. Signal Processingc. Calibration

12

5). Detector Factorsa. Positionb. Orientationc. Aperture Sized. Head Frequency

Let’s discuss every factor one by one.

Contaminant Factors

a. The most important factor affecting working of metal detector is the contaminant material. The key properties essential for metal detection are:-

1. Electrical Conductivity- is the ability of a body to conduct electricity.σ = 1/ρ

2. Magnetic Permeability- Measure of the ability of substance to support the formation of magnetic field.μ = μo x μr

The magnetic properties play a more dominant property in detection.

13

Below is the decreasing order of conductivity of some metals:

SilverCopperGold

AluminiumZinc

NickelTin

ChromiumLead

Mercury

Property Matrix

14

Good Conductors( σ)

Bad Conductors( σ)

b. Another factor that affects the working is size and shape of the contaminant material. It is usually observed that spherical objects are detected with more difficulty and wires are detected easily.

Detector Factors

a. Orientation effect-

15

1. Easy for non-ferrous2. Difficult for ferrous

1. Easy for ferrous2. Difficult for non-

ferrous

b. Position effect-

d. Aperture size- Lower the aperture size, higher is the sensitivity of metal detector and vice-versa.

16

At centre magnetic field is weak and objects are

difficult to detect

At sides the magnetic field is the strongest and

easily detected

Aperture Size

e. Head Frequency-

Installation Factors

a. Metal Free Zones- This place a very important role in the proper functioning of the metal detector. The Metal free Zones are classified in two categories:-

MFZ 1 (For non moving metal particles)

MFZ 2 (For moving metal particles)

17

Higher the Frequency, Higher the Sensitivity

Lower the Frequency, Lower the Sensitivity

Detects

Stainless Steel

High Rates of

False Rejectio

ns

MFZ 1 (For non moving metal particles)

MFZ 2 (For moving metal particles)

18

b. Vibrations- High level of mechanical vibrations causes an increase in the number of false strikes.

c. Clearance- Here clearance can be detected as the vertical distance from throat to chute. It should be at least 10mm. Clearance is necessary for performing of validation test and for expansion/movement of flexible product chute.

d. Electromagnetic/Radio Frequency Interference

Another Detector

(AM Receiver)

Inverter Motors,

Clutch/Brake and Power

Cables

Fluorescent Lamp

Mobile Phone and

Walkie Talkie

Air-Borne Disturbances

in Environment

EM/RF Interfere

nce

19

Note- Metal detectors are very sensitive to AM radio receiver.

Product Factors

a. Moisture- Water is a good conductor of electricity. It may cause a false metal strike, if moisture is present in high concentration. Rejected products may test negative after a few days as the particles could have been broken or product dry up. So it detection gets difficult.

b. Recipe- If the product is rich in mineral matter, faulty metal detections often appear at a fast rate.

Electronic Factors

Factors such as detection threshold, fault in signal processing system and calibration error also plays important role in the proper functioning of metal detectors.

20

Alignment of Metal Detector with FSMS Plan

In current scenario, metal detector has become an active part of all FSMS plans. Metal detector has turned out into a CCP essential. It is used to track particles of size more than 1mm.

The online testing of metal detectors should be carried out in the following manner:-

1. Hazard- Metal Particles2. Location- All filing lines3. Specification- Correct functioning of metal

detection system and should detect operating limit defined by the factory. Critical Limit is SS 2.0mm.

Note- The test piece should be spherical and certified by the supplier for both operational and critical limits.

CCP monitoring procedure:-1. Check proper functioning of metal detector at

least once per shift with standard spherical test pieces of operational limit.

2. Ensure that the product incriminated by the metal detector is kept separately and sorted by offline metal detectors.

21

3. Metal retrieved from the rejections are retained and root cause analysis is done.

4. Record for online testing, offline testing and retrieved metal pieces.

5. In case of increasing number of metal retrievance proper correcting action should be taken by the production/engineering section.

Action in Case of Deviation

1. Incase the metal detector fails in the routine check, than stop the line.

2. Check the detector with 2mm SS, if it passes than release the product since last check and recalibrate the detector.

3. If detectors fails with 2mm SS, block the product since last check.

4. Pass the product through offline metal detector.

5. Incinerate the rejections and rework the unrejected ones.

22

Limitations of Metal Detectors

23

Limitations

Sensitivity

Can only detect metal

contaminants

To be detected the metal diameter should be

greater than 1mm

Installation

Needs a bigger vertical space

Performance is affected by

noise and vibrations

References

1. www.metaldetection.com/subtwo140.html

2. www.wikipedia.en/metaldetector.html

3. Gaur, R.K. and Gupta, S.L. 2003. Engineering Physics. Dhanpat Rai Publications.

4. Potter, N.N. and Hotchkiss, J.H. 2007. Food Science. CBS Publishers & Distributors.

5. Alli, I. 2004. Quality Assurance:Principles and Practices. CRC Press LLC.

24