Coin discrimination apparatus with compensation for external ambient conditions

Coin discrimination apparatus comprising:

• means defining a path for passage of a coin under test;
• sensor coil means for forming an inductive coupling with said coin under test during its passage along the path;
• drive means for generating an oscillatory electrical signal across the coil sensor means;
• detecting means responsive to the amplitude of the oscillatory signal across the sensor coil means in the absence of a coin, for producing an ambient condition signal (t) which is a function of an ambient condition for the sensor coil means;
• control means responsive to the amplitude deviation of the signal across the sensor coil means produced as a result of the inductive coupling between a coin traveling along the path past the sensor coil means, for providing a coin signal (x) which is a function of a characteristic of the coin uncompensated for the effects of said ambient condition;
• compensating means for modifying the coin signal (x) to produce a compensated coin signal (y) according to the following equation:
• y=k((c.sub.1 x+c.sub.2)t+x)+c.sub.3
• where
• k, c.sub.1, c.sub.2, c.sub.3 are constants;
• memory means including at least one set of reference data for said compensated coin signal (y);
• and
• means for determining whether the compensated coin signal (y) is in a predetermined relationship with said reference data and providing an output indicative of whether the coin is acceptable.