Speed Sensor Technologies Principles

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Speed Sensor TechnologiesPrinciples
Applications
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Content

• Sensing principles
• VR
• Hall
• Eddy current
• Targets
• Pole wheels
• Pole bands
• Speed sensing General issues
• Typical Setup
• Prerequisites
• Design parameters
• Applications

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Typical Speed Sensor Setup

• Alignment sensor to target

Radial
Axial
Speed sensor
Target
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Sensing Principles

• (Electro) magnetic sensing principles for
  demanding applications
• Robust high vibrations, high temperatures
• Non contact
• Free of maintenance
• Measurement principles
• Variable reluctance (VR)alternative names
  inductive, electromagnetic
• Hall Effect (HA, alternatively MR)
• Eddy Current (EC)
• Actively induced
• Passively induced

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Measurement Principle Variable Reluctance

• Magnetic flux is changed depending on teeth or
  gap
• Change of magnetic flux induces voltage in coil
  amplitude and frequency of output signal depends
  on rotational speed
• Output signal is influenced by (for a given
  sensor)
• Rate of change of magnetic flux (speed)
• Air gap
• Geometry of target
• Electrical load

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Simulation Results for Magnetic Field
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Hall Effect

• Conductor in magnetic field
• 1 Electrons
• 2 Hall element
• 3 Magnets
• 4 Magnetic field lines
• 5 voltage source

Source Wikipedia
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Measurement Principle Hall Effect

• Sensor head is magnetically biased and works with
  a magnetizable pole wheel
• Hall element measures the magnitude of the
  magnetic field
• If tooth is in front of sensor -gt large magnetic
  field
• If gap is in front of sensor -gt small magnetic
  field
• Change of magnetic field depends on the geometry
  of the pole wheel

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Measurement Principle Eddy Currents

• EC - Eddy Current Active (Nova)
• Oscillator
• Frequency and amplitude of oscillator is
  influenced by presence of conducting material
• EC - Eddy Current Passive (Hermes)
• Conductor moving in magnetic field (e.g. turbine
  blade)
• Voltage induced -gt eddy currents -gt changing
  magnetic field around eddy currents -gt voltage
  induced in sensor coil

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Continuous Operating Temperature

• Short time (ECVR) up to 300C

VR
125C
-40C
240C
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Pole Wheels and Pole Bands

• Pole wheels
• Most important factor for sensing module
• Geometry
• Typical involute gears
• Other geometries are possible
• Pole bands
• Is mounted on a rotating shaft
• Designed for applications where no pole wheel can
  be used, often for large shafts (diameter gt 0.5
  m)
• Jaquet provides both pole wheels and pole bands

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Pole Wheels Involute Gear
Z number of teeth do (mm) Z module (mm) dk
(mm) (Z2) module (mm) module (mm)dk /
(Z2) p module p
Typical gears Module 1, 2 and 3
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Prerequisites

• Target
• Material is attracted by magnets (i.e. high
  magnetic permeability)
• Electrically conductive (eddy currents)
• Rotation
• Typical signal frequency range 0 - 20 kHz
• Air gap
• Depends on geometry of target
• Typically 0.5 - 1.5 mm
• Input stage of customer electronics

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Parameters of Speed Sensors

• Ambient conditions
• Temperature range
• Air gap and target geometry
• Frequency range
• Target magnetic/nonmagnetic
• Sensor
• Protection fast transients, false polarity,
  short circuit
• Output signal rectangle, raw signal
• Rotational symmetry yes / no
• Direction detection
• Redundancy
• Size
• Packaging Steel, epoxy

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Components of Sensors

• Measuring device (coil or Hall element)
• Energy (magnet, electrical oscillator)
• Electronics and/or electrical connection within
  sensor housing
• Interface
• Connector
• Cable
• Mechanical parts
• Housing
• Potting material
• Sealing material

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Components
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Main Applications VR

• Turbochargers
• Trucks (Cummins, Honeywell, BorgWarner)
• High temperature
• High volume (100000-500000 pieces/year)
• Ships (ABB)
• Turbines
• Helicopter
• Airplanes
• Diesel engines

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Main Applications Hall-Sensors

• Single channel
• Turbines
• Diesel engines (large)
• Cam shaft
• Crank shaft
• Industrial applications
• Hall effect (2 channel)
• Hydraulic pumps
• Differential Hall effect (2 channel)
• Brakes (railway)
• Propulsion (railway)

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Main Applications EC

• EC active
• Power turbines (blade counting)
• Turbochargers (blade counting)
• Trucks
• EC passive
• Turbochargers (blade counting)
• Trucks
• Passenger cars