A complex set of variables affect metal detection and detection sensitivity. Some physical characteristics of metal objects that influence detection are material composition, shape, surface area, surface and internal electrical and magnetic properties, and finish. The orientation of a test object can greatly influence detection as can the direction and speed or changes in speed while passing through the detection zone. Nearby large metal objects and metal moving in near proximity to a metal detector also affect operation, as do temperature and humidity, and can be a cause for nuisance alarms. Additionally, most currently manufactured walk-through metal detectors have some means for programming the operation of the detector for special conditions or requirements; these variables and the effect they have on the operation of in-plant detectors must be considered if a test program is to be effective. This practice is intended to minimize the impact of these variables on the operation of in-plant detectors by systematically testing the installed detectors in the operating environment with the test object(s) specified by the regulatory authority requirements.
This practice may be used to determine the critical test object from a group of test objects, its critical orientation, and the critical test path through the detection zone. This information may allow the use of a single test object for setting the operational sensitivity of the detector and performing periodic performance evaluations necessary to ensure a high probability that all test objects in the group are detectible within the capabilities of the detector.
The detection sensitivity map(s) generated by this practice provides baseline metal detection data for the specified test objects and can serve as a foundation for in-plant walk-through metal detector set-up and performance evaluation testing. The detection sensitivity map(s) may be incorporated into a detector performance test log in support of performance evaluation practices.
This practice may provide insight into certain metal detection characteristics of walk-through metal detectors, particularly the effect of different metals and test object orientations on detection capability, that are useful for optimizing detector sensitivity settings for detection of specified weapons or shielding material, or both.
Periodic performance of this practice and analysis of the results may provide a means to monitor the state of health of in-plant detectors and to gain further insight into detector application and operation.