Loosely Coupled and Context-aware Service Provision Incorporating the Quality of Rules

A proximity detector comprises a parallel oscillatory circuit the inductance of which is influenced by the metallic element of which it is desired to ascertain the distance, this oscillatory circuit forming part of an oscillator. The oscillator is fed with constant current; current is injected into the oscillatory circuit through a negligibly small resistance; and the output signal is taken off at the output terminals of the oscillator; the device is used to provide an analog signal which is a linear function of distance, in order to classify articles or to measure their speed of approach.