Selecting a detection system
There are many criteria to consider when evaluating metal-detection systems for tablet and capsule processing. Perhaps the
most important is the system's sensitivity (i.e., how small a metal fragment can be detected [the typical range for pharmaceutical
applications is less than 0.5 mm]) and how immune the system is to outside influences such as vibration and electromagnetic
noise, which can cause false rejects (see Table I). When selecting the size of the system's aperture, one should consider
performance as well as throughput and size to avoid product jams during production.
Table I: Typical detectable metal diameter versus metal detector's aperture size.
One subtle, but important, factor to consider when evaluating different systems is what, if any, effect a product might have
on the metal detector. Most tablets and capsules look like "dry" products to the metal detector, but it is possible that they
may trigger a false reject if they contain significant concentrations of metal elements such as iron. If a false reject continually
occurs, the detector's operating threshold can be desensitized, but this change may reduce the system's performance. Before
selecting a system, therefore, it is important to test the complete system on all of the pharmaceutical products that may
be used to determine how the system will perform in a production setting.
Once it is determined that a system can detect the smallest fragments of metal possible with no chance of false rejection,
there are other aspects of the system to consider to ensure that it can be successfully used in a particular production process.
Table II provides a list of key questions to ask when evaluating a system.
Table II: Key criteria for selecting a pharmaceutical metal detection system.