The security of the nation’s banking sector has recently come under focus, as banks have become targets of hoodlums and armed
robbery attacks. In a changing world like ours today, crime is on the increase and the effectiveness of the security outfits in the nation is far below expectation. To solve this hydra-headed problem, state-of-the-art security gadgets can be used and one of such is the personnel metal detector. Metal detectors have many different uses ranging from security systems, detecting studs in walls to searching for archeological artifacts or treasure buried in the ground. There are also many applications in industries.
Most simple metal detectors and some more specialized types make use of proximity effects whereby the presence of a metal close to a search coil modifies the characteristics of the circuit. Metal detectors of the Beat Frequency Oscillator or BFO type operate using this principle. The detector is based on the principle that the resonant frequency of a tuned circuit varies if a metallic object is placed in close proximity. If the tune circuit forms part of the oscillator then output frequency will be modified by the presence of a metallic object. The variation in output frequency depends on the oscillator frequency chosen. Although the higher the frequency of oscillator the greater the change, and hence the higher the sensitivity of the circuit If the frequency is too high, the practical range may be reduced by the absorption effects of the soil, building materials e.t.c. In a practical circuit, the oscillator often operates at a frequency well outside the range of human hearing and therefore it is necessary to provide some indication that the resonant frequency is changed. BFO metal detectors do this by mixing or beating the output of the oscillator with that of a second (fixed frequency) oscillator to produce a mixing product or beat note within the audio range. The frequency of one of the two oscillators is adjustable to allow the most appropriate frequency to be selected. When a metal object is detected, the frequency of the search coil oscillator changes producing an audible output corresponding to the difference in frequency between the two oscillators. When used in this way, the detector will effectively be less sensitive as slight changes tend to result in only small changes in frequency. Therefore the audio note produced may be below audible frequency range. Depending on the design and coupling, the two oscillators may be automatically locked to the same frequency. If this occurs, a considerable change in the resonance of the search coil tuned circuit is required to pull the oscillators out of lock and unto different frequencies. This effect results in reduced sensitivity of the system. The effectiveness of the security outfits in the nation has fallen far below expectation. Killings, arson and mayhem are the order of the day with hoodlums keeping people in fear. This is a nation under siege. To solve this hydra-headed problem, state-of-the-art security gadgets can be used and one of such is the personnel metal detector using a voltage comparator. This device is designed to be hand-held and easy to operate. The internal circuit is designed to be triggered when a metal comes in close proximity to a search coil, which forms part of a colpitt oscillator. The sensitivity of the device can be increased using a variable resistor and a varied inductance. An alarm/indicator system beeps to indicate metal detection. This simple but effective device is cheap, its materials can be sourced locally, it does not use any material with harmful radiations hazardous to health, it can be easily maintained, and hence used by security operatives. The developed system has its applications in banks; transport agencies, homes and security induced restricted places. This device will greatly improve the efficiency of our security outfits in the 21st century.