Inductive Loop Detector Technology

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Inductive Loop Detector Technology

• Detecting Traffic for
• nearly 45 years

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A Brief History

• Detection of vehicles since the early 1960s
• Designs based on solid-state analog loop
  technology using discrete components i.e.
  transistors, diodes, etc.
• Loops varied in size from small loops to large
  loops
• The size of the loop is dependent upon the
  requirements of the control system

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History continued

• Smaller loops were typically used with volume
  density controllers where vehicle count
  information was needed to vary the timing of
  traffic signals
• By the early 1980s digital loop detectors were
  replacing the earlier analog loop detectors.

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The IL (Inductive Loop)
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The IL (Inductive Loop)
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How it works

• When a vehicle reaches the loop, the metal of the
  vehicle disturbs the magnetic field over the loop
• This disturbance causes the loop inductance to
  change

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The figure below illustrates the distinguishing
double-hump characteristic of ground vehicles.
                                                 
                     
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Yeah but???

• The size of the loop, shape of the loop, number
  of turns in the loop coil, and the length of the
  lead-in wire all combine to form a specific
  circuit
• The current passing through the loop generates an
  electromagnetic field. When a vehicle passes
  through the field, it acts as a conductor,
  changing the inductance of the loop.
• The sensor detects this change and notifies the
  traffic-signal controller of its finding.

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Today

• New software-based detector designs utilize the
  latest available state of the art
  microprocessor technology. An area of
  significant importance, which benefits from the
  new microprocessor technology, is in accurately
  gathering and processing inductive loop
  signature information.
• Each vehicle having a different shape, which
  passes over the inductive loop embedded in the
  pavement, produces a different signature. The
  inductive loop signature can provide valuable
  information about different shaped vehicles
  passing over the loops. This information can be
  utilized by traffic control systems to increase
  the responsiveness of those systems.

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For more information

• www.renoae.com
• www.romanse.org.uk/technologies/loops.htm
• http//www.tfhrc.gov/pubrds/septoct98/loop.htm
• http//www.geocities.com/SiliconValley/Port/2945/T
  raffic/TrafficSensors.htm
• http//www.faa.gov/and/and400/and410/lot/concept.h
  tm