Some control action requires information on the direction of the vehicle. Two loops must be used to determine vehicle direction and a dual channel detector may have built-in direction logic. This logic outputs on separate relays depending on vehicle movement in direction “A to B” or “B to A”. This direction logic is commonly known as A-B logic.

Nortech dual channel detectors can be configured for A-B logic operation, refer to the user guide for details.

ASB stands for “Automatic Sensitivity boost”. This means that the “un-detect” sensitivity level will be at the maximum sensitivity setting when ASB is enabled, regardless of the selected sensitivity. This enables highclearance vehicles to remain detected as they pass over the loop.

The ability of a vehicle detector to automatically tune to an inductive loop on application of power.

Cross-talk refers to the interference between detectors that are oscillating at similar frequencies. If the frequency of adjacent loops on different detectors is within 1 kHz of each other, there could be interference, causing false detects to occur. The frequencies need to be separated by changing the frequency settings on the detector.

Fail-safe means that the detector relays are energised in the “un-detect” state, and de-energised in the “detect” state. Thus in the event of a power failure, the detector will revert to a “detect” state. Therefore a parking garage boom gate will be raised during a power failure.

Fail-secure means that the detector relays are de-energised in the “un-detect” state, and energised in the “detect” state, thus in the event of a power failure, the detector will revert to an “un-detect” state. Therefore a parking garage boom gate will remain lowered during a power failure.

An inductive loop is a coil of wire buried in a roadway that creates a magnetic field when connected to a vehicle detector. This magnetic field is able to sense the metal content of a motor vehicle passing over the loop coil. This change in magnetic field causes the detector to operate.

The loop feeder is the length of cable that connects the loop in the ground to the detector module. In most parking applications the loop and feeder is a continuous length of wire. Where the two ends of the loop emerge from the slot cut in the roadway, these ends are twisted together and routed to the detector. Where the feeder runs a longer distance (up to 100 meters in length) the feeder of usually a separate screened twincore cable.

When the detector is powered and connected to a loop, the output contacts are “normally – open” and “close” when a vehicle is detected. A closed contact will pass current and operate the controlled device (door or gate). Some control strategies require an output that is “normally-closed” (NC) and open with the arrival of a vehicle. NC contacts require a special part-number at time of order or an internal wiring modification to a standard detector.

Automatic Frequency Selection allows the detector to automatically scan and select the best operating frequency that will achieve the lowest loop noise and maximum signal strength.