Torque and Power Measurement

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Torque and Power Measurement
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Need?

• Applications for torque sensors include
  determining the amount of power an engine, motor,
  turbine, or other rotating device generates or
  consumes
• Used in stress and deflection analysis
• Determining the performance characteristics of
  machines
• Called dynamometers

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classification

• Absorption type dynamometers measures torque by
  absorbing mechanical energy. Power generator may
  be engine or motor
• Driving type Dynamometer is power generator.
  Like electric motor or generator. Used to measure
  power required to drive unit.
• Transmission type passive device. Neither
  generates nor absorbs

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Absorption type Dynamometers

• Water brake
• Hydraulic
• Rope brake
• Prony brake
• Eddy current

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• A dynamometer consists of an absorption (or
  absorber/driver) unit, and usually includes a
  means for measuring torque and rotational speed.
  An absorption unit consists of some type of rotor
  in a housing. The rotor is coupled to the engine
  or other equipment under test and is free to
  rotate at whatever speed is required for the
  test. Some means is provided to develop a braking
  torque between dynamometer's rotor and housing.
  The means for developing torque can be
  frictional, hydraulic, electromagnetic etc.
  according to the type of absorption/driver unit.

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• One means for measuring torque is to mount the
  dynamometer housing so that it is free to turn
  except that it is restrained by a torque arm. The
  housing can be made free to rotate by using
  trunnions connected to each end of the housing to
  support the dyno in pedestal mounted trunnion
  bearings. The torque arm is connected to the dyno
  housing and a weighing scales is positioned so
  that it measures the force exerted by the dyno
  housing in attempting to rotate. The torque is
  the force indicated by the scales multiplied by
  the length of the torque arm measured from the
  center of the dynamometer.

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Eddy current

• When a current carrying conducting material moves
  through a magnetic field voltage is generated,
  which results in current.
• If the conductor is a part of circuit then
  current will flow through circuit. But if it is
  isolated than voltage is still induced local
  currents may flow in a short circuited path
  within the bar itself. These current are called
  eddy eddy currents, dissipated in the form of
  heat.

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