• Metal detectors can suffer from vibration, interference and mineral false positives.detector de metales image by Marco Antonio Fdez. from Fotolia.com
  
  Metal detectors use electromagnetic fields to detect various types of metal that are out of sight, most often buried in the ground. These fields are produced by a battery and the user can change the properties of the field and the sensitivity of the device by using its controls. When set correctly, metal detectors are effective, but there are several issues beyond calibration that can plague the devices.
  
  

Batteries

• Most metal detectors require specific alkaline batteries to operate. If the wrong battery is used, the metal detector will not be able to function correctly: it may give off a constant positive signal, or it may refuse to operate at all. As the battery gradually loses its charge, the detector may become more and more erratic.
  
  

Minerals

• Metal detectors are used to find specific metal objects in the ground. However, some minerals in the ground can also interfere with the detector's sensors, especially metallic elements. Iron, for instance, is found in several different types of deposits and may be common near coal or other mines. Minerals like iron will give false positives and users may think that something is wrong with the detector itself.
  
  

Wiring

• Metal detectors work using tightly wound coils of wire to generate magnetic fields. Sometimes, especially with older devices, these wires can come undone or burn out. This causes the detector to fail or malfunction. It may stop working intermittently, or weaken so that it cannot sense any metal. Users with internal problems like this usually must replace their detectors completely.
  
  

Interference

• Any electromagnetic field can cause interference problems with metal detectors. If there are any power lines nearby, the electric noise these lines produce will distort the detector's field and make accurate readings impossible. Smaller devices like motors and large household appliances may also cause problems. Metal detectors often have noise suppression features, but the interference can still cause problems.
  
  

Vibration

• Sensitive metal detectors react badly to vibration, such as shaking and jarring movements. Sometimes this alters the metal detector controls, and sometimes this causes a false positive signal. Users should handle their metal detectors carefully and avoid sudden movements or vibration (such as a car trip) when the detector is calibrated.