Some engineers have been known to drive their spouses batty pulling up to a traffic light sensor (a coil of wire set into a rectangle of pavement cuts) and rocking the car. They try to change the magnetic field generated and sensed by the coil in order to get a green light sooner. Occasionally this manuever makes a difference, but in northern climes sometimes the temperature extremes and thermal expansion differences in the ground cause the coils to break or the pavement to move, cutting the wires.
Now thanks to Banner Engineering (http://rbi.ims.ca-3846-532), a patented sensor based on magnetoresistive technology eliminates having to use a wire loop in the road surface and the required pavement cuts to install it. The M-GAGE® S18M detects 3D changes in the Earth's magnetic field when a large metal object is present, causing the sensor's outputs to switch.
The sensor is housed in an 18-mm diameter ABS/polycarbonate-blend molded housing. It can be installed in a conduit positioned below the pavement during construction or in an above-grade location. No external controller is needed and the sensor, which is push-button programmed, automatically "learns" its installation environment, determining background conditions and storing them in onboard, non-volatile memory.
The latest version of the detector comes in a "flat-pack" housing. Aimed at the retrofit and repair market, it can be used in existing traffic control systems to upgrade them or replace broken coils. The thin package permits the sensor to be installed in a pavement saw cut.
Scott Spinger, Banner product manager, says M-GAGE applications also include
detection of vehicles at car wash entrances and exits, and drive-up kiosks.
Industrial uses are at tractor-trailer loading docks and for vehicles such as
forklifts passing through automatic overhead doors.
Point Sensor: Without needing a wire
loop, the ferromagnetic vehicle sensor has less to go wrong.