Note: Descriptions are shown in the official language in which they were submitted.
CA 02710041 2015-01-28
VEHICLE DETECTION SYSTEM
[0001] The present invention relates to systems for detecting and processing
information generated
by moving objects. More specifically, various embodiments of the application
relate to systems and
methods for detecting and processing information generated by on-track
vehicles including
locomotives, train cars of all types and railroad maintenance and inspection
vehicles.
[0002] BACKGROUND OF THE INVENTION
100031 Methods for warning motor vehicle operators at highway-rail grade rail
crossings are
either passive or active. Passive warning methods at public crossings are
often required by law to
include the statutory crossbuck sign posted for each direction of traffic
traversing the tracks.
Alternative signs may be posted in addition to the crossbuck sign, such as
number of tracks signs,
"Do Not Stop on Tracks" signs, "Look for Trains" signs, statutory yield signs,
statutory stop signs,
and railroad crossing advance warning signs. The roadway surface can be
painted with stop bars and
railroad crossing symbols. Warning devices at private roadway crossings of
railroad tracks can be
provided by the roadway owner or the railroad and may be absent altogether or
can be any
combination of passive or active devices identical to those used at public
crossings or of unique
design. Active warning devices, by example, can be a warning bell, flashing
red lights, swinging red
lights, gate arms that obstruct roadway vehicle lanes, solid or flashing
yellow advance warning
lights in combination with statutory crossbuck signs, number of tracks signs,
railroad advance
warning signs, various informational signs, and pavement markings.
Historically it has been cost
prohibitive to include active warning systems at every grade crossing, thereby
limiting many grade
crossings to have merely passive warning systems.
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[0004] Conventional railway systems often employ a method which uses track
rails as part of a
signal transmission path to detect the existence of a train within a defined
length or configuration
of track, commonly referred to as track circuits. The track rails within the
track circuit are often
an inherent element of the design of the circuit because they provide the
current path necessary to
discriminate the condition of the track circuit which is the basis of train
detection.
[0005] A conventional track circuit is often based upon a series battery
circuit. A battery,
commonly referred to as a track battery, is often connected to one end of the
track circuit and a
relay, commonly referred to as a track relay, is connected to the other end of
the track circuit.
Current from the track battery flows through one rail of the track circuit,
through the coil of the
track relay and back to the track battery through the other rail of the track
circuit. As long as all
elements of this system are connected, the track relay will be energized.
Typically, an energized
track relay corresponds to the unoccupied state of the system in which a train
is not present
within the track circuit. In the event that a train does occupy the track
circuit, the series track
battery-track rails-track relay circuit becomes a parallel circuit in which
the wheels and axles of
the train provide a parallel path for current flow between the two track rails
of the circuit. Most
current flows in this new circuit path because its resistance is very low
compared to the track
relay resistance. As a result, the track relay cannot be energized if a train
occupies the rails
between the track battery and the track relay. A significant advantage of this
system is that if the
current path between the track battery and the track relay is opened, the
track relay will not be
energized. Common causes of track circuit failure with typical railroad fail-
safe circuits that may
interrupt the current path include broken rail, broken wire connections
between the battery or
relay and the rail, broken rail joint electrical bonds, and failed battery
power. Should any
element of the circuit fail, the signal control element, typically the track
relay, will revert to the
safest condition, which is de-energized. The typical track circuit is also an
example of railroad
signal closed circuit design. All elements of the circuit are necessary and
only one current path is
available to energize the track relay.
[0006] The track battery/relay circuit is often the basic functional unit for
railroad signal system
design. The energy state of track relays provides the fundamental input to the
logical devices that
control automatic signal systems, including wayside train signal, crossing
signal, and interlocking
operation.
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[0007] Previously known methods for detecting trains that approach highway-
rail grade
crossings monitor and compare track circuit impedance to a known audio
frequency signal. The
signal is continuously monitored by the train detection unit which is tuned to
an unoccupied track
(normal state) during installation. Signal strength and phase within certain
limits produce an
energized output that corresponds to an unoccupied track circuit. When signal
strength and/or
phase are not within the normal state limits the train detection unit output
corresponds to an
occupied track circuit. A train occupying the track circuit changes the
impedance of the circuit.
The change vector for a moving train correlates to position of the leading or
trailing wheels and
axle of the train in the track circuit, train direction and speed.
[0008] The most advanced of such devices are capable of providing a "constant
warning time"
control for highway grade crossing signal operation. One of the advantages of
this method at its
most advanced application is the ability to cause crossing signals to operate
for a predetermined
time prior to the arrival of a train at a crossing roadway regardless of train
speed. This device
may provide multiple, independently programmable outputs which may be used
control separate
and independent systems. One output can be programmed to control the actual
operation of the
railroad crossing signal and the second output can be programmed to provide
the appropriate
input to a separate traffic light system that governs motor vehicle movement
at an intersection
near the railroad crossing.
[0009] In one aspect, a vehicle detection system detects roadway vehicles and
an action is taken.
Often the action taken is to adjust the frequency of intersection light
operation in response to
changing traffic patterns. It is common that roadway conditions can change
dramatically as a
result of a traffic accident, draw-bridge operation, or a train passing. As a
result the rate of speed
for the roadway vehicles is dramatically reduced, and often stopped. The slow
rate of speed and
common stoppage of traffic commonly is not accurately detected by certain
magnetic field
detectors.
[0010] In another aspect of vehicle detection systems trains are detected and
active railroad
signal crossing warning devices are activated to warn traffic at highway-rail
grade crossings, and
therefore advanced preemption of the warning devices is necessary. However, a
major
disadvantage to the use of known loop detectors is that they do not reliably
detect slow-moving
objects passing through the magnetic field. It is often the case that
railroads require trains to stop
for periods of time. Due to the size and mass of trains they do not have the
ability to accelerate
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quickly from a stopped position. Therefore it is often the case that trains
move at a slow rate of
speed. One of the inherent problems associated with certain magnetic field
detector is that a
requisite minimum rate of speed prevents detection of slow moving objects.
[0010.1] According to one aspect of the invention, there is provided a
railroad train detection
system comprising:
a plurality of sensor devices fixed in proximity to a railroad track, wherein
the plurality of sensor
devices define a train detection zone, wherein each sensor device comprises:
a first anisotropic magnetoresistive (AMR) sensor configured to generate AMR
waveform data representative of changes in a generally constant magnetic field
environment due
to the presence of a railroad train within a sensing range of the first AMR
sensor; and
signal processing apparatus configured to process AMR waveform data generated
by the
first AMR sensor; and
a control processor, wherein the control processor is configured to:
receive AMR waveform data from the plurality of sensor devices; and
apply a detection algorithm to AMR waveform data received from the plurality
of sensor
devices to determine whether a train is present in the train detection zone.
[0010.2] According to another aspect of the invention, there is provided a
railroad train
detection system comprising:
a first sensor device and a second sensor device fixed in proximity to a
railroad track,
wherein the first and second sensor devices define a train detection zone;
the first sensor device comprising:
a first sensor device anisotropic magnetoresistive (AMR) sensor configured to
generate AMR waveform data representative of changes in a generally constant
magnetic
field environment due to the presence of a railroad train within a sensing
range of the first
sensor device AMR sensor;
a bias compensator configured to compensate for changes in the first sensor
device AMR sensor; and
first sensor device signal processing apparatus configured to process AMR
waveform data generated by the first sensor device AMR sensor;
the second sensor device comprising:
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=
a second sensor device AMR sensor configured to generate AMR waveform data
representative of changes in a generally constant magnetic field environment
due to the
presence of a railroad train within a sensing range of the second sensor
device AMR
sensor;
a bias compensator configured to compensate for changes in the second sensor
device AMR sensor; and
second sensor device signal processing apparatus configured to process AMR
waveform data generated by the second sensor device AMR sensor; and
a control processor, wherein the control processor is configured to receive
AMR
waveform data from the first and second sensor device signal processing
apparatus by
applying a detection algorithm to AMR waveform data received from one or more
of the
first and second sensor devices to determine whether a train is present in the
train
detection zone.
[0010.3] According to another aspect of the invention, there is provided
a railroad train
detection system comprising:
a plurality of anisotropic magnetoresistive (AMR) sensors fixed in proximity
to a railroad
track, wherein the plurality of AMR sensors define a detection zone;
wherein each AMR sensor is configured to generate analog waveform data
representative
of changes in a generally constant magnetic field environment due to the
presence of a railroad
train passing in the detection zone on the railroad track;
signal processing means configured to generate digital waveform data based on
analog
waveform data generated by the plurality of AMR sensors; and
a system processing apparatus, wherein the system processing apparatus is
configured to:
receive AMR waveform data from the plurality of sensor devices;
apply a detection algorithm to AMR waveform data received from the plurality
of
sensor devices to determine whether a train is present in the train detection
zone.
100111 It would be advantageous to have a vehicle detection system
that is failsafe and detects
the presence of trains whether stopped, or moving at any speed. It would be
further advantageous to
have such a system available at a reduced cost as compared to conventional
systems.
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BRIEF DESCRIPTION OF THE DRAWINGS
[0012] Figure 1 is a conceptual schematic of the present invention for a
highway-railroad
grade warning device control system in accordance with at least one embodiment
of the present
invention.
[0013] Figure 2 is a block diagram of a sensor node in accordance with at
least one embodiment
of the present invention.
[0014] Figure 3 is a block diagram of a control processor in accordance
with at least one
embodiment of the present invention.
[0015] Figure 4 is a flow chart identifying steps in a method for sensing,
processing and
transmitting data by the sensor node to the control processor in accordance
with at least one
embodiment of the present invention.
[0016] Figure 5 is a flow chart identifying the steps in a method for
processing the data
transmitted by the sensor nodes in accordance with at least one embodiment of
the present
invention.
[0017] Figure 6 is a flow chart identifying the steps in a method for the
control processor health
checks in accordance with at least one embodiment of the present invention.
[0018] Embodiments of the invention are described below with reference to
the accompanying
drawings, which are for illustrative purposes only. Throughout the views,
reference numerals are
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used in the drawings, and the same reference numerals are used throughout
several views and in
the description to indicate same or like parts or steps.
DETAILED DESCRIPTION OF THE INVENTION
[0019] In the following detailed description, references are made to the
accompanying drawings
that form a part thereof, and are shown by way of illustrating specific
embodiments in which the
invention may be practiced. These embodiments are described in sufficient
detail to enable those
skilled in the art to practice the invention, and it is to be understood that
other embodiments may
be utilized and that structural, logical and electrical changes may be made,
[0020] An embodiment of a vehicle detection system 10 is represented in Figure
1. The system
includes sensor devices 12, 14, 16, 18, each sensor device 12, 14, 16, 18 has
a pair of sensor
nodes 24, 26, and a control processor 28. Bath of the sensor nodes 24, 26 is
placed in proximity
to the railway track 20, which crosses a roadway 22. Data from the sensor
nodes 24, 26 is
communicated through wireless transmission and reception with the control
processor 28_ The
wireless connection 28 can be chosen from a variety of wireless protocols, by
example, 900
/v1HZ radio signals. The system 10 is not limited to a specific number of
sensor nodes 24, 26.
Sensor nodes need not be paired as in this embodiment, and devices 12, 14, 16,
18 can
alternatively have more than 2 sensor nodes 24, 26.
[00211 Referring now to Figure 2, the sensor devices 12, 14, 16, 18 include
one or multiple
sensor elements 30, an amplifier module 32, and analog to digital converter
34, a microprocessor
module 36, a bias compensation module 38 and a radio module 40. The sensor
devices 12, 14,
16, 18 can be single or multi-dimensional. One or more sensor nodes 24, 26 can
be connected to
the sensor device 12, 14, 16, 18. The sensor nodes 24, 26 receive data and
transmit the data to
the sensor devices 12, 14, 16, 18. The radio 40 sends data from the sensor
device 12, 14, 16, 18
to the control processor 28. The microprocessor module 36 receives digital
data from the analog
to digital converter 34 and encodes the data in packets for transmission by
the radio 40. The
sensor element 30 provides a continuous sigrlial to the amplifier module 32
which filters and
amplifies the analog waveform for processing by the analog to digital
converter 34. The
microprocessor 36 also continuously receives data from the bias compensation
module 38 and
controls elements of a resistive network to maintain optimum bias for the
sensor element 30.
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Data Conditioning enhances the signal to noise ratio of the sensor output by
various filtering
techniques such as Kalman, Infinite Impulse Response, and Finite Impulse
Response filters. The
Kalman filter is an advanced filtering technique that enhances the signal to
noise ratio and
eliminates unexpected signal variation. The filtered signal can also be
amplified. Alternatively,
the combination of sensor node 24, 26 and sensor device 12, 14, 16, 18 can be
referred to as a
sensor.
[0022] The sensor devices 12, 14, 16, 18 and control processor 28 can be
placed at locations a
significant distance from power lines, making it inconvenient for traditional
power sources. A
fuel cell system (not shown) can be connected to the paired sensors 12, 14,
16, 18 and control
processor 28 to provide operating power. Alternatively, a photo voltaic system
may be
substituted for the fuel cell system. Alternatively, other sources of power
can be used to provide
power to the paired sensors 12, 14, 16, 18 and control processor 28.
[0023] Now referring to Figure 3, the control processor 28 includes vital
processing module 42,
communication module 50, vital I/O modules 48, user interface module 44,
diagnostic testing
and data logging module 52, and remote operations module 46. The vital
processing module 42
can be a central processing unit (CPU) that may be selected from a variety of
suitable CPUs
known in the art. Alternatively, module 42 can be two or more redundant CPUs.
The
communications module 50 receives data transmitted from the sensor devices 12,
14, 16, 18,
exchanges data with VPU module 42, and with warning system peripheral devices
(not shown).
The vital I/O module 48 provides a vital interface control of conventional
railroad signal relays
or control devices that can be connected to the control processor 28. The
diagnostic testing and
data logging module 52 can provide a variety of user interface options,
including, by example,
RS232, USB, Ethernet, and wireless technologies, to facilitate user access to
control processor 28
to enter site specific information, select appropriate user variable values,
perform set-up and
diagnostic testing and to review or download data log files. Data can be saved
on dedicated hard
drive, flash memory module, CD ROM drive or other devices appropriate to the
intended
environment. The user interface module 44, by example, can be a software
module that provides
configuration options, firmware update, device programming and debugging. The
remote
operations module 46 can provide the interfaces for remote communications with
the system 10,
using cellular or satellite channels. The module 46 can provide, for example,
remote status
checking, alarm notification, limited configuration and data transfer. The
communication
module 50, remote operations module 46 and user interface module 44 provide
communications
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security and adaptability to a variety of communications protocols that can be
executed by the
system 10.
[0024] The sensor nodes 24, 26 are configured to respond to the presence of
vehicles. The
Earth's magnetic field is used as a magnetic background or "reference" point
which stays
substantially constant when the sensor nodes are installed in a fixed
arrangement. Adjustments
can be made in the event substantial constant magnetic offsetting, other than
the Earth's magnetic
field, occur near the sensor nodes 24, 26. Vehicles which are constructed of,
or contain, hard
and/or soft-iron materials affect the earth's magnetic flux. Hard-iron sources
are materials that
possess flux concentration abilities and can have remnant flux generation
abilities. Soft-iron
materials are often considered to be ferrous materials that concentrate
magnetic flux into material
and do not have any remnant flux generated within the material. Based upon
relatively distinct
hard and soft-iron composition of a vehicle the sensor element 30 will
encounter a relatively
small (in the range of milligauss) Earth field bias along with relatively
large (in the range of 3-4
gauss) spikes as typical vehicles come into range of the sensing element. When
vehicles are near
the sensor nodes 24, 26, the change in the magnetic field causes the three
dimensional sensor
element to produce an output along the three dimensions of space that
correspond to the amount
and rate of change of field monitored by the sensor element 30. The waveforms
generated along
the three axes are determined by the magnetic characteristics of the vehicle
sensed.
[0025] The sensor nodes 24, 26 can be configured to generate data which
corresponds to the
direction of a moving vehicle. The system can utilize one or more sensors in
order to obtain
vehicle direction data. With a single sensor element configuration, as a
vehicle approaches the
sensor the flux density changes and the sensor output is proportional to the
change. The sensor
output waveform is substantially a mirror image for the same vehicle moving in
the opposite
directions.
[0026] The configuration of system 10 at a particular installation may depend
on, but not limited
to, sensor node 24, 26 depth, pair spacing, and positioning distance from the
railroad track.
These parameters influence the three dimensional waveform data generated by
sensor nodes 24,
26. The system 10, once configured, can obtain information pertaining to the
passing vehicle
such as vehicle speed, direction, length or size of the vehicle. The system 10
can detect,
distinguish between and identify vehicles. The sensor element output data from
a locomotive
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engine will be significantly different from a rail car, and type of rail car,
such as a box car or tank
car will generate detectably different sensor element output data.
[0027] Regarding a two or more sensor configuration the sensor nodes 24, 26
are typically placed
a relatively small distance from one another. A range of 10-20 meters or
alternatively 5-12
meters is suitable. The distance can be user determined based upon a variety
of variables
including the type and use of the vehicle detection system 10. A suitable
sensor node 24, 26
placement can also be about one foot to several meters distance from each
other. Further
distances between sensors can provide additional advantages, including
increased calculation
data for analyzing vehicle travel and position. Often a vehicle in motion will
create the same
signature, merely displaced in time. In one embodiment of the invention, a
multi-sensor
configuration 12, 14, 16, 18 generates a multiplicity of sensor node 24, 26
data that can be
analyzed to produce a multidimensional representation of the magnetic fields
at specific locations
within and at the limits of the system 10 detection zone. Such analysis
enables criteria to be
established which correspond to each of the possible on-track vehicle events
that can occur
within the detection zone of on-track vehicles. The events of interest include
on-track vehicles
moving in one direction or the other, stopping and reversing direction within
the zone, stopping
within the zone, speed of movement including speed changes within the zone.
Number,
placement and configuration of sensor nodes 24, 26 detennine the resolution
detail of the
detection zone representation possible for a particular system 10. The level
of resolution
required depends upon the accuracy needed to determine specific events within
specified
timeframes. Ultimately, system 10 layout is a signal engineering design task
and is based upon
the identified requirements of the specific location where system 10 is to be
installed.
[0028] The data is analyzed vitally by the system 10 for the purpose of
detecting oncoming trains
in advance of their travel through grade crossings. The analysis and
subsequent decisions and
inferences made from vital data processing ensure proper and safe operation of
the railroad
crossings.
[0029] Now referring to FIGS. 4-5, the system 10 is initialized at step 54.
The sensor nodes 24,
26 produce a signal at step 56 whenever any on-track vehicle is within range.
The sensor nodes
24, 26 apply the signal to a low pass noise filter and adjust the dynamic
range through a low
noise instrumentation amplifier at step 58. The resulting waveform is
processed by high
precision analog to digital converters at step 60. The digitized waveform is
organized into fixed
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length data frames containing sensor ID, packet length, and CRC checksum by a
microprocessor
at step 62. The data packets are transmitted to the control processor at step
64. The control
processor 28 is initialized at step 66 and receives the data at step 68. The
processor 28 decodes,
and filters data transmitted by the sensor nodes 24, 26 at step 70. Waveform
data from all of the
sensor nodes 24, 26 is compared and processed by a detection algorithm at step
72, in order to
determine classification, speed and direction of the sensed vehicle. In the
event that the detected
data satisfies, at step 74, criteria requiring warning system activation, the
nomial output of the
vital output controller is de-energized at step 76. The output of the vital
output controller is
energized if there are no on-track vehicles present and the system reverts
back to the ready state
after step 66. This is often referred to as the normal state of the system.
The de-energized output
of the vital output controller 76 corresponds to an alarm state and will
result when event criteria
for on-track vehicles within the detection zone are satisfied or from internal
faults of any element
of the system 10.
[0030] The warning sequence execution includes the step of removing a normally
high output
signal from the control interface with the crossing warning device (not
shown). As a result, the
crossing warning devices for any on-track vehicle approaching or occupying the
crossing
roadway are activated. On-track vehicles moving away from the crossing roadway
or stopped on
the approach to the crossing roadway will not typically cause the crossing
warning devices to
activate. The warning device can be any combination of active railroad
crossing signals.
100311 The on-track vehicle must be within the sensing field of a sensor node
to be detected.
The data received at step 68 from each of the sensor nodes placed for a
specific detection zone is
processed at step 70 via detection algorithm to determine presence location
and speed of an on-
track vehicle and the necessary state of the vital output controller 76. The
algorithm results that
correspond to an on-track vehicle moving toward the crossing zone, where the
arrival is predicted
within a user specified time, cause the normally energized vital output
controller output to be de-
energized. If any of the system elements or devices fail to provide data or
output that
corresponds to non-presence of an on-track vehicle or to a stopped on-track
vehicle or to an on-
track vehicle that is moving away from the crossing zone, the control
processor 28 will interrupt
the vital output controller 76, causing the crossing signals to activate. This
feature maintains a
fail safe system and therefore the default position for the system is the
warning signal activation,
which will occur if any part of the system 10 fails to operate within preset
parameters.
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[0032] Referring to FIG. 6, the control processor 28 performs a health check
protocol at regular
intervals to assure the system is operating properly. The health check
protocol is utilized at step
78. Data from each sensor node 24, 26 of the system 10 must be received,
decoded and
identified at step 80 by the control processor 28 within a user selected
interval range of about 1 to
4 seconds or the output of the vital output controller is disabled at step 86.
The processor module
is comprised of redundant microprocessors and associated hardware. Each of the
processors
monitor the heartbeat of the other processors at step 82. All microprocessor
heartbeats must
agree or the vital output is disabled at step 86. The vital output controller
84 is comprised of
redundant microprocessors, associated hardware and relay driver circuits. The
microprocessors
each monitor the heartbeat of the other processors at step 84. All
microprocessor heartbeats must
agree or the vital output is disabled at step 86. The microprocessor heartbeat
can be the clock
signal. If all health check requirements are satisfied and the data processing
algorithm result is
consistent with no current or pending on-track vehicle occupancy of the grade
crossing, the vital
output of the control processor is enabled at step 88. Alternatively, the time
interval range can be
about 2-10 seconds.
[0033] In one aspect of the system at least two sensor nodes 24, 26 are
positioned in close
proximity to one another and strategically placed with respect to the grade
crossing and warning
device. Transmission of the data from the sensor nodes 24, 26 can be performed
through a
variety of known technologies. One exemplary manner of transmission includes
short-range
spread spectrum radio 40. Radio signal transmission is preferably at about 900
MHZ. A secure
radio signal transmission link can be provided for increased security.
[0034] Waveform data transmitted from the sensor nodes 24, 26 are analyzed
through advanced
processing techniques. Specific placement of the sensor nodes 24, 26 with
respect to the railroad
track or roadway affects the waveform detail produced by the sensor node.
Sensitivity of the
sensor node is determined by inherent characteristics of the physical sensor,
the configuration of
the resistive bridge element and by the voltage applied.
[0035] When the system 10 contains more than one sensor node 24, 26 placed
between railroad
crossings, it is possible for the sensor devices 12, 14, 16, 18 to function
with respect to greater
than one grade crossing control device. Since the system 10 is capable of
detecting direction of
travel, a train traveling in either direction with respect to the sensor nodes
24, 26 can be detected
and analyzed.
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[0036] The information acquired by the sensor nodes 24, 26 can include a
variety of information
depending upon the type and calibration of the sensor nodes 24, 26. Suitable
sensor nodes include
the AMR sensors manufactured by Honeywell. Alternatively, one suitable type of
sensor node 24,
26 is a 3M Canoga Model C924TE microloop detector. The 3M Canoga detector
detects vehicle
presence and movement through an inductive loop.
[0037] Additionally, the sensor nodes 24, 26 are configured to reduce the
incidence of falsing due to
environmental, component, or supply voltage variations. Incorrect detection of
vehicles is referred to
as falsing. The sensor nodes 24, 26 dynamically update the 'bias' value of the
sensor element by
detecting the proper bias and changing the existing bias value when a user
defined threshold results.
Through dynamic bias updating the system more accurately maintains the
distance between the bias
value and the detection threshold value. Without dynamic bias update there is
an increased risk that
the detection threshold value will result in either false positive or false
negative detection.
[0038] Variation in environmental temperature can cause falsing to occur. The
sensor node 24, 26 is
comprised of the sensor element 30, amplifier 32, biasing element 38,
microprocessor 36, and analog
to digital converter 34. The microprocessor 36 controls the feedback and
compensation circuits 38
necessary to maintain the optimum detection condition of the sensor. The
biasing element 38 is
typically a negative magnetic flux generating coil that allows minute
discrimination of changes in
the bias voltage applied to the sensor element 30 by the microprocessor 36.
The microprocessor 36
adjusts the voltage to this coil to provide dynamic compensation 36, 38. The
sensor element 30
output waveform is amplified 32 and applied to an analog to digital converter
34 and the result is
encoded into packets by the microprocessor 36 for transmission by the sensor
node radio 40. The
automatic bias compensation circuits 36, 38 enable the sensor element 30 to
operate in its optimum
range when placed into environments where there are extreme variations of
temperature, humidity,
and flux density.
[0039] The various embodiments are given by example and the scope of the
invention is not
intended to be limited by the examples provided herein.
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