| 摘要 |
At a point on the path of a first voltage signal used to warn of a metal object towards the unit used to signal the warning, this first signal is detected and a second voltage signal with an opposite character to the first signal is sent to a point along the first signal path upstream from the point where the first signal is detected. A summation is made at this upstream point between the first and second signals and the resulting 0-signal is sent via the first signal detection point to the warning unit. Metal objects passing through a measuring coil (8) cause a change in magnetic field, resulting in a corresponding detection voltage signal being generated to alert the presence of the object. Low frequency signals caused by disturbance are ignored and only those signals with frequencies typical for metal objects are analysed. An Independent claim is also included for the detection device. |
