Abstract: Means for hinging or removably attaching a cover to a chassis comprising a retainer device including a pair of arms spring-urged away from one another. The retainer device is fixed to the chassis with the ends of the arms extending outward into openings in the cover. The arms can be manually pinched to disengage them from the cover openings to thereby permit the cover to be removed from the chassis. Utilization of a pair of retainer devices on the chassis enables one of the devices to be disengaged while the other remains engaged to thus hinge the cover relative to the chassis.

Abstract: Apparatus for use in combination with an inductive loop for detecting metal objects, e.g. vehicles, in the immediate vicinity of said loop. The loop may, for example, be a coil of wire buried in a roadway in a plane parallel to the roadway surface. Oscillator circuitry is operatively connected to the loop with the frequency of oscillation being determined by the loop inductance, which in turn is dependent on whether or not the vehicle is over the loop. The loop frequency is monitored by digital circuitry including a loop counter which counts loop oscillator cycles and a duration counter which measures the time duration of a fixed number of loop oscillator cycles. The measured time duration is compared with an adaptable reference duration to ascertain whether the loop oscillator frequency has increased or decreased. The presence of a vehicle over the loop decreases loop inductance, increases loop frequency, and thus reduces the measured time duration of a fixed number of loop cycles.

Abstract: An improved inductive loop structure useful for detecting metal objects such as vehicles on a roadway. The two terminal loop is formed by a conductive wire configured to define two substantially rectangular paths lying side by side in a common plane such that respective sides of the two paths lie adjacent one another. Alternating current is supplied to the terminals of the wire to produce a commonly oriented magnetic field around the adjacent sides of the rectangular paths and an oppositely oriented magnetic field of lesser magnitude around each of the outer sides of said rectangular paths. As a consequence, the field components interact to enhance field strength within the area bounded by said outer sides and reduce field strength outside of that area.

Abstract: Apparatus for use in combination with multiple inductive loops for detecting metal objects, e.g. vehicles, in the immediate vicinity of each of said loops. Each loop may, for example, be a coil of wire buried in a roadway in a plane parallel to the roadway surface. A common oscillator circuit is operatively connected to each loop on a time shared basis with the frequency of oscillation at any time being determined by the inductance of the connected loop. The inductance in turn is dependent on whether or not a vehicle is over the loop. Successive scan cycles are defined with multiple loop phases occurring during each scan cycle.