Vehicle detector system with presence mode counting

Claim 1

In a detector system in which objects are detected in a detection area using an inductive sensor and an oscillator having a oscillator signal that is a function of the inductance of the inductive sensor, a method for detecting subsequent vehicles in the detection area during presence of at least one other vehicle in the detection area, comprising: (a) determining presence of a first vehicle in the detection area when a counted number of cycles of the oscillator signal during a first measurement period differ from a first reference value by at least a first threshold amount; (b) activating a presence call signal when the first vehicle is determined to be present and maintaining the presence call signal for as long as at least one vehicle is determined to be present; (c) setting a current in-call reference when the presence call signal is active wherein the current in-call reference is based on the counted number of cycles during the first measurement period, wherein the in-call reference is in addition to and not substituted for the first reference value; (d) setting a current in-call threshold when the presence call signal is active, (e) determining presence of a subsequent vehicle in the detection area when a counted number of cycles of the oscillator signal during a subsequent measurement period differ from the in-call reference by an amount at least equal to the in-call threshold wherein the in-call reference is updated during the detection of each subsequent vehicle.