Magnetometer vehicle detector

• US 5,491,475 A
• Filed: 03/19/1993
• Issued: 02/13/1996
• Est. Priority Date: 03/19/1993
• Status: Expired due to Term

• Current Assignee: Honeywell Incorporated (Honeywell International Inc.)
• Original Assignee: Honeywell Incorporated (Honeywell International Inc.)
• Inventors: Volna, William M., Rouse, Gordon F.
• Primary Examiner(s): Crosland, Donnie L.
• Application Number:
  US08/034,440
• Time in Patent Office: 1,061 Days
• Field of Search: 340/933, 340/939, 340/940-943, 340/665, 340/666, 324/244, 324/207.15, 324/207.21, 324/207.23, 324/242, 324/243, 324/244, 324/245, 324/251, 324/256, 324/655, 364/436-438
• US Class Current: 340/933
• CPC Class Codes: G08G 1/042 using inductive or magnetic detectors

Abstract

A magnetometer vehicle detector for detecting various parameters of traffic on a roadway. A number of sensors, having a compact package, along with connecting cables, may be placed in road way with a small number of standard width sawcuts. Alternatively, sensors may be placed in the roadway within tubes under the external surface of the roadway. The package design of the sensor is such that the sensor can be placed in the sawcut or tube only in a certain way or ways resulting in the most sensitive axis of the sensor being most likely affected by just the traffic or vehicles desired to be detected and measured. The sensor may be a magnetoresistive device having a permalloy magnetic sensing bridge. Multiple sensors may be placed in single or multiple lanes of the roadway for noting the presence of vehicles and measuring traffic parameters such as average speeds, vehicle spacings, and types and numbers of vehicles. Such information is processed from the shapes, times and magnitudes of the signature signals from the sensors.

Claims

1. A magnetometer vehicle detector, for a roadway having at least one lane, comprising:

at least one magnetometer sensor in each lane; and

wherein said magnetometer sensor comprises;

a magnetoresistor bridge, having a sensitive axis, outputting an electrical signal caused by a change of resistance in the magnetoresistor bridge due to a change of an ambient electromagnetic field, the change caused by a presence of a vehicle;

an amplifier connected to said magnetoresistor bridge for outputting an amplified electrical signal indicating the presence or absence of a vehicle;

an integrator connected to said amplifier for outputting an integrated electrical signal indicating the change of the ambient electromagnetic field and the presence or absence of a vehicle;

a feedback coil connected to said integrator and proximate to said magnetoresistor bridge for providing a magnetic feedback to said magnetoresistor bridge;

a reset coil proximate to said magnetoresistor bridge for switching a magnetization axis of said bridge between zero and 180 degrees alternately with respect to the sensitive axis; and

a signal line connected to said integrator for conveying the signal indicating the presence or absence of a vehicle.

2. The detector of claim 1 wherein the magnetometer sensor fits into a standard sawcut in the roadway wherein the sensitive axis has a direction that is approximately perpendicular to a common surface of the roadway.

3. A magnetometer vehicle detector for a roadway having first and second surfaces and at least one lane on the first surface comprising:

at least one magnetometer having a sensing axis situated in each lane of the roadway; and

wherein;

said magnetometer comprises;

a bridge of magnetoresistors having a sensitive axis and resistance variations caused by changes of an ambient magnetic field caused by an occurring presence of a vehicle;

an amplifier connected to said bridge of magnetoresistors for enhancing voltage changes caused by the resistance variations of said bridge;

an analog-to-digital converter connected to said amplifier;

a signal line connected to said analog-to-digital converter; and

a signal processor connected to said signal line;

each said magnetometer fits in and is situated in a sawcut in the roadway at the first surface, having the sensing axis approximately perpendicular to the surface;

at least a portion of each signal line is situated and fits in the sawcut in the roadway; and

said amplifier comprises;

an integrator; and

a feedback coil, connected to said integrator and proximate to said bridge of magnetoresistors, for providing magnetic feedback to said bridge, for reducing effects of cross-axis sensitivity and non-linearity upon said bridge.

4. The detector of claim 3 further comprising a reset coil proximate to said bridge of magnetoresistors for switching magnetization of said bridge of magnetoresistors relative to the sensitive axis, for reducing effects of thermal drifts and offsets upon said bridge.

5. A magnetometer vehicle detector, for a roadway, comprising at least one magnetometer, situated in the roadway, having four magnetoresistors connected end to end in a form of a bridge having first, second, third and fourth nodes, the first and third nodes connected to a positive and negative voltage supplies, respectively, and the second and fourth nodes connected to inverting and non-inverting inputs of an amplifier, with a direct current provided to the inputs of the amplifier due to a resistance change of the four magnetoresistors caused by a vehicle proximate to or passing near said magnetometer, and resulting in an output signal from the amplifier thereby indicating a presence of the vehicle;

and wherein;

each of said plurality of magnetometers has given distances from the other magnetometers along a length of the roadway;

a signal processor that receives groups of output signals having signature characteristics from said plurality of magnetometers which are caused by vehicles proximate to or passing near said plurality of magnetometers, and converts the signals into information of numbers of vehicles and speeds of the vehicles;

said signal processor converts signature characteristics of the signals into classification information on each of the detected vehicles;

said signal processor converts signature characteristics of the signals into classification information on each of the vehicles;

said signal processor comprises;

a multiplexer connected to said plurality of magnetometers;

an analog-to-digital converter connected to said multiplexer; and

a microcomputer connected to said analog-to-digital converter; and

said microcomputer comprises;

first means, connected to said analog-to-digital converter, for determining first times between peaks of the signals;

second means, connected to first means, for determining vehicle speeds from the first times and the given distances;

third means, connected to said analog-to-digital converter, for determining second times between groups of the signals;

fourth means, connected to said second and third means, for determining vehicle spacings from the vehicle speeds and the second times;

fifth means, connected to said analog-to-digital converter and having predetermined signal threshold values, for determining third times by comparing the signature characteristics of the signals with the predetermined signal threshold values;

sixth means, connected to said fifth means, for classifying the third times into vehicle types; and

seventh means, connected to said sixth means, for determining vehicle counts.

6. The detector of claim 5 further comprising a modem connected to said second, fourth, sixth and seventh means.

7. The detector of claim 6 wherein the magnetometers are magnetoresistive detectors.