FIELD OF THE INVENTION
The present invention relates to a method for detecting metal contamination in bakery
food products.
More particularly, the present invention relates to a method and apparatus for detecting
iron, non iron and stainless steel metal contamination in bakery food products.
BACKGROUND AND PRIOR ART
In the bakery industry, conventionally the discrimination of the contaminated biscuit is
•carried out by metal detectors. Though X-rays detection is another well known available
solution but is refrained from using due to its inherent inhumane characteristics. Metal
detectors with different capabilities of detection are being used with the biscuit carrying
conveyors passing through it with different linear speeds. The high speed of conveyor
specifically in the order of 15-20 meters/min has been a reason for stable and consistent
performance of the metal detectors wherein the metal contamination could be easily
detected.
The progress of technology has taken metal detectors from valves to transistors, to
integrated circuits and more recently into microprocessors. Thus this has increased their
performance giving greater sensitivity, stability and flexibility, as well as widening the
range of output signals and information they provide.
However, present day metal detectors are still unable to detect every particle of metal
passing through them.
Thus there is a need to provide a method and apparatus for high speed and accurate
detection of metal contamination present in the bakery product if any.
The present inventors have surprisingly found that the apparatus of the present invention
maintains high speed and accuracy and prevents false signaling.
OBJECTS OF THE INVENTION
It is an object of the present invention to overcome the drawbacks of the prior art.
It is another object of the present invention to detect metal contamination in dry cream
biscuits to prevent dispatching of faulty products.
It is another object of the present invention to provide a feasible, reliable and repeatable
solution at the desired conveyor speed.
SUMMARY OF THE INVENTION
Accordingly, the present invention relates to a metal detector capable of sensing the metal
contamination wherein the said detector demonstrates a conveyor linear speed of 2
m/min.
Another aspect of the present invention is to provide a higher detection and amplifier
circuit boards to prevent false signaling and maintaining accuracy.
DETAILED DESCRIPTION OF THE INVENTION
The present invention relates to a method for detecting metal contamination of bakery
products. The operation of the metal detector is based on the principle of electromagnetic
induction. A metal detector comprises of one or more inductor coils that are used to
interact with metals on the ground. A pulsing current is applied to the coil, which then
induces the magnetic field, as shown in the blue. When the magnetic field of the coil
moves across the metal, the field induces electric current, which generates an opposite
current in the coil and induces the signal indicating the presence of the metal.
The principle object of the present invention is to design an equipment capable of
detecting the metal contamination in the dry cream biscuits to prevent the bad biscuits
going into the market and delivering feasible, reliable and repeatable solution at the
desired conveyor speed of 2 meters/min. The speed is controlled and maintained by
applying variable frequency drive (VFD) to the motor driving the conveyor at desired
level. The accuracy of the equipment is directly proportional to the speed of the conveyor
and thus if the speed falls below 2 meters/min the performance accuracy of the metal
detector will deteriorate.
Whenever any metal comes in the vicinity of the electromagnetic field and penetrates the
electromagnetic lines generated by the transmitter coil. Due to very less linear speed of
the metal on the conveyor the rate of change of magnetic flux is very less and thereof the
magnitude of eddy currents as well.
The power that causes eddy current in the metal comes from the electromagnetic field
resulting in power loss, which is sensed by the detector circuits and confirms the presence
of the metal contamination. A normal microprocessor detector designed for any ordinary
metal detector is not capable of sensing this unbalance signal of transmitter and receiver
coil wherein the rate of change of magnetic flux is very less.
Accordingly, the present invention prevents false signaling by maintaining accuracy by
means of a higher detection and amplifier circuit boards. The said amplifier circuit board
is a circuit, which amplifies the input analog signal to multiple folds to make the
detection circuit possible to discriminate the healthy and faulty signals generated by the
sensing circuit of any equipment.
Metal detectors distinguish metal objects from each other based on the ratio of their
inductance to their resistivity. This ratio gives rise to a delay in the receive signal at a
given operating frequency and linear speed. An electronic circuit called a phase
demodulator measures this delay. In order to separate two signals, such as the ground
component and the target component of the receive signal, as well as to determine the
likely identity of the target, two such phase demodulators whose peak response is
separated from each other by one fourth of the transmitter period, or ninety degrees. As
the transmitting speed is very slow in these detectors hence the chances of noise pickup is
very prominent. Special filter circuit has been used to attenuate and filter these noise
levels. A microprocessor based system is used to monitor and determine the target's
likely identity, and assigning it a number. This ratio is having a resolution of better than
500 to 1 over the full range of conductors with different conductivity.
Ground balance
Presence of salts dissolved in the ground water, results in a strong signal received by the
metal detector due to the ground itself which may be thousands of times stronger than the
signal resulting from small metal objects buried at modest depths. A ground balancing
circuit has been arranged within the metal detector, so that even if the strength of the
ground signal changes dramatically the metal detector's output remains constant.
Accurate ground balance makes it possible to pinpoint the location of the targets with a
good deal of precision and to search in a non-discriminate or "all-metal" mode, accurate
ground balance is essential.
Discrimination Of Target And Ground Signals
Although the ground signal may be much stronger than the target signal, the ground
signal tends to remain the same. On the other hand, the target signal will rise quickly to a
peak and then subside. This require techniques to separate ground from target signals by
looking at the rate of change of the receive signal rather than looking at the receive signal
itself. As the speed of the rate of change of signal is very slow and hence the detection of
'these signals become cumbersome and requires a circuit with high resolution and
accuracies.
Microprocessor Control
The microprocessor is a complex electronic circuit, which performs all of the logic,
arithmetic, and control functions necessary to control and monitor the operations of a
metal detector. A sequence of stored instructions is performed by the microprocessor, one
at a time to perform the desired functions.
We claim:
1. A metal detector capable of sensing metal contamination in bakery
product wherein the said detector demonstrates a conveyor linear speed of
2 m/min.
2. The metal detector as claimed in claim 1 wherein the conveyor linear
speed is controlled by applying variable frequency drive to the motor
driving the conveyor.
3. The metal detector as claimed in claim 1 wherein said detector comprises
higher detection and amplifier circuit boards to maintain accuracy and
prevent false signaling
4. The metal detector as claimed in claim 1 wherein the circuit board
amplifies the input analog signal to multiple folds.
5. The metal detector as claimed in claim 1 wherein the microprocessor
based system is used to monitor and determine the target's likely identity
and assigning it a number.

A metal detector capable of sensing the metal contamination wherein the said detector demonstrates a conveyor linear speed of 2 m/min provide a higher detection and amplifier circuit boards to prevent false signaling and maintaining accuracy.