Metal Detector and Challenge Test

The presence of metal pieces even in trace quantity may degrade drugs, medicine and nutrients. For example, Vitamin-C i.e. ascorbic acid and chemically known as L-3-keto-threo-hexuronic acid lactone and a-tocopherol, are  degraded due to the presence of trace amount of copper and iron. In fact, ascorbic acid as well as a-tocopherol is also destroyed either by heating and or oxidation. Other factors viz., moisture content and pH also influence the degradation of vitamin-C includes.  Cort et al. (Ref: Cort, W.M., Mergens, W. and Greene, A., Stability of alpha- and gamma-tocopherol:   and   interactions. Journal of Food Science, 43(3):797–798) reported that both a- and ? -tocopherols were degraded by and Chelating compounds such as ascorbic acid and Ethylene-Di-ammine-Tetra Acetate (EDTA) appeared to inhibit the  oxidation, while ascorbic acid prevented the  oxidation of tocopherols in alcohol solutions.

Though various metals powders are used as catalyst in the synthesis of various drugs, medicine and nutrients e.g., the formation of stable complexes of anthocyanins with tin, copper, and iron have been suggested by Sarma et al. (Ref.: Sarma, A.D., Sreelakshmi, Y. and Sharma, R. 1997. Antioxidant ability of anthocyanins against ascorbic acid oxidation. Phytochemistry, 45(4):671–674) to increase the stability of these compounds in the presence of metals, the separation of metal catalysts is must from the final product not only for the stability of the products but also for the safety of the consumers.

In the manufacturing of tablets and capsules, there is a chance of contamination of metal pieces either ferrous or nonferrous, tramp metal i.e. digger teeth, axe heads etc. in their final form. It is important to detect the various metallic impurities that may be present in such tablets and capsules before final packing, as the medicine must be free from all impurities including metallic parts.  The presence of unwanted metal parts not only degrades the product quality but also their presence may be dangerous as they can damage expensive equipment. Thus, the pharmaceutical industry like other industries viz., food, chemical, coal, ceramic, aggregates, mineral processing, plastic and rubber and packaging needs highly accurate metal detection device to meet the requirements of demanding consumers and stringent legislation. There are different types of metal detectors; some are suitable for self-monitoring online metal detection.

Metal detectors are designed for simple, reliable, sensitive and capable to detect magnetic as well as non-magnetic metals, flexible operation and compatible with tablet press, auto balance, efficient on-line detection as well as rejection or separation of metallic impurities system. The metal detection system should be easily cleaned and hygienic. The metal detector system should occupy less installation space and should be located before or after the packing of tablets and capsules, syrups and other liquid medicines. Normally, the metal detectors are designed for the compliance with GMPs, with multiple aperture sizes and the ability to detect 0.2 mm or even less metal spheres and come with easy-to-use suitable size VGA touch screen interface with advanced digital signal processing to provide detailed analysis and reporting for process applications including pharmaceutical, food, chemical, coal, ceramic, aggregate, mineral, plastics and packaging industries. Some metal detectors are used to detect metals in bulk products  under free-fall conditions to protect machineries viz., extruders, spherodizers, injection moulding, blow moulding and fine grinding mills and quality control and inspection of intermediate products, granules, ate, reclaim, bagging stations, dryers and packing stations.

Working principles

Metal detectors available for use in pharmaceutical and food industries are working in different principles. Different working principles of different metal detectors are discussed briefly discussed in the following sections.

Balanced coil metal detector: 

The working principle of balanced coil metal detector is based on the balance of current flowing in three coils. The transmitter coil generates a field, acts as a radio transmitter. The second coil is the receiver, connected to a third coil, called detector. If a metal particle, present in the filed generated by first coil even in trace quantity; gets ‘illuminated’ which is diagnosed and detected by the second and third coils respectively. The response is related to the conductive and magnetic properties of the metal. Control system normally mounted on the search head, or located remotely; depending on the design and the application. When a typical metal particle is illuminated, the signal at the receiver coils is one millionth of a volt. First this is amplified by a high performance RF amplifier, modulated down to low frequency. This provides amplitude and phase information. Finally the signals are digitised and digitally processed, to optimise the sensitivity.

Magnetic field metal detector: 

Earlier the magnetic field metal detectors were developed mainly for detecting ferrous metals viz., iron and steel. But, now they can detect nonferrous metals in drugs, medicines, nutrients and foods also. When a magnetised particle passes under these detector, a current is generated which is amplified by the electronics of the detection system, and the same is used to trigger the detection signal output. Secondly, if any conductive material is present in a magnetic field, it generates signals for non-magnetic metals, which is detected by the detector. However, only large pieces of nonferrous metals and stainless steel are detected. So in the vast majority of applications, this technology is only applicable to the detection of ferrous metals.

The user interface in the magnetic field detector, provides the means of communication with the system, allow set up and optimise the detector to operate the system in any environment and mechanical handling system. Microprocessors are used to provide a wide range of communication links, statistical analysis and system information.

Pulse induction metal detector: 

The working principle of pulse induction metal detector is based on the principles of electromagnetic induction. Pulse induction metal detector detectors contain one or more inductor coils that are used to interact with metallic elements on the ground. The single-coil detector illustrated below is a simplified version of one used in a real metal detector. The pulse induction is sensitive to both ferrous and non-ferrous metals and does not offer any discrimination between the two. It is relatively insensitive to foil and similar thin conductive items and very sensitive to coins, rings, and other small objects. Larger objects, of course, are easily detectable at considerable depth. pulse induction systems either use a single coil as both transmitter and receiver, or more (two or even three) coils working together. This type of metal detector sends powerful, short bursts (pulses) of current through a coil of wire. Each pulse generates a brief magnetic field. When the pulse ends, the magnetic field reverses polarity and collapses very suddenly, resulting in a sharp electrical spike. This spike lasts a few microseconds (millionths of a second) and causes another current to run through the coil. This current is called the reflected pulse and is extremely short, lasting only about 30 microseconds. Another pulse is then sent and the process repeats. A typical pulse induction-based metal detector sends about 100 pulses per second, but the number can vary greatly based on the manufacturer and model, ranging from a couple of dozen pulses per second to over a thousand.

If the metal detector is over a metal object, the pulse creates an opposite magnetic field in the object. When the pulse's magnetic field collapses, causing the reflected pulse, the magnetic field of the object makes it take longer for the reflected pulse to completely disappear. This process works something like echoes: A sampling circuit in the metal detector is set to monitor the length of the reflected pulse. By comparing it to the expected length, the circuit can determine if another magnetic field has caused the reflected pulse to take longer to decay. If the decay of the reflected pulse takes more than a few microseconds longer than normal, there is probably a metal object interfering with it. The sampling circuit sends the tiny, weak signals that it monitors to a device call an integrator. The integrator reads the signals from the sampling circuit, amplifying and converting them to DC. The direct current's voltage is connected to an audio circuit, where it is changed into a tone that the metal detector uses to indicate that a target object has been found.

Pulse induction-based detectors are not very good at discrimination because the reflected pulse length of various metals is not easily separated. However, they are useful in many situations in which other non pulse induction based metal detectors would have difficulty, such as in areas that have highly conductive material in the soil or general environment. Also, pulse induction-based systems can often detect metal much deeper in the ground than other systems.

Types Of Metal

Following types of metal are detected and removed by the pharmaceutical metal detectors.

Stainless steel

Ferrous

Aluminum

Copper

Bras

Challenge Test Procedure for Metal Detector:

Switch on the power supply, now passes the dummy sample. It should be a pass.

Then pass SS, Fe, and Non-ferrous one by one. It should be rejected.

Note: If the metal detector test failed, immediately stop the machine and inform the head of the department and QA Department and immediately raise a request for breakdown. Put the “under breakdown” label on the metal detector.

Frequency of challenge test:

At the start of the batch and then every two hours alternatively by production and QA.

End of a batch by Production and QA.

After the breakdown.

Metal detector challenge test for Capsule:

Metal Use to do the challenge test for the Capsule is:

Fe (Ferrous)- 0.60 mm

N-Fe (Non-Ferrous)- 0.80mm

SS( Stainless steel AISI 316)- 1.00mm non-magnetic

Dummy: Without metal particles and has no diameter

Follow the above Procedure to do the challenge test for Capsule.