Torque Sensor or Torque Transducer or Torquemeter is a device for measuring and recording the torque on a rotating system, such as an engine, crankshaft, gearbox, transmission, motor, rotor, or a bicycle crank. Torque Sensors are used in applications monitoring machine tool efficiency and electric motor efficiency. Static torque is relatively easy to measure. Dynamic torque, on the other hand, is not easy to measure, since it generally requires transfer of some effect (electric or magnetic) from the shaft being measured to a static system.

Torque Sensor Types and Torque Measurement Technologies

  • Strain Gauge Torque Transducers – These Torque Sensors or Torque Transducers use strain gauges applied to a rotating shaft or axle. With this method, a means to power the strain gauge bridge is necessary, as well as a means to receive the signal from the rotating shaft. This can be accomplished using slip rings, wireless telemetry, or rotary transformers. Newer types of torque transducers add signal conditioning electronics and an A/D converter to the rotating shaft. Stator electronics then read the digital signals and convert those signals to a high-level analog output signal, such as +/-10VDC. Strain Gauge Torque Transducers provide high accuracy to both rotational torque and reaction torque measurements, and their high cost and bulkiness are features which have limited their use primarily to research and development laboratories and in quality assurance testing in order to verify standards. Strain
  • Magnetoelastic Torque Sensors – One way to achieve the torque measurement is to condition the shaft or a member attached to the shaft with a series of permanent magnetic domains. The magnetic characteristics of these domains will vary according to the applied torque, and thus can be measured using non-contact sensors. Such Magnetoelastic Torque Sensors are generally used for in-vehicle applications on racecars, automobiles, aircraft, and hovercraft.
  • Surface Acoustic Wave (SAW) Sensors are wireless sensors used for remotely sensing the torque, strain, load force, etc. The strain on these tiny devices as the shaft flexes can be read remotely and output without the need for attached electronics on the shaft.
  • Twisted Angle Torque Sensor – Another way to measure torque is by way of twist angle measurement or phase shift measurement, whereby the angle of twist resulting from applied torque is measured by using two angular position sensors and measuring the phase angle between them.
  • Piezoelectric Torque Sensor – The Piezoelectric Torque Sensor uses piezoelectric effect to measure the strain instead of strain gauge. They are compact and very versatile.

Reaction Torque Sensors and Rotating Shaft Torque Sensors

Reaction Torque Sensors are suitable for a wide array of torque measurement applications. Reaction torque sensors are particularly useful in applications where the introduction of inertia due to a rotating mass between the driver motor and driven load is undesirable. Due to the fact that these sensors do not utilize bearings, slip-rings, or other rotating elements, their installation and use can be very cost effective. They are typically used in torsional test machines, motor dynamometers, or in any application where rotation is limited to 360° or less.

Rotating Shaft Torque Sensors are designed to mount in-line between a driving source, and an absorber, or load. They are used in engine dynamometers, electric motor testing, hydraulic pump testing, fan testing, and a multitude of other applications.