DEFINITIONS

Below are a list of technical definitions that are fundamental for the understanding of how Binsfeld's wireless torque telemetry works.

Strain

Strain is a unitless measurement of how much an object deforms due to an applied force.

  • Strain = Change in length / Starting length = 
Poisson's Ratio

Poisson's Ratio is a material-specific constant that relates the transverse deformation (strain) to axial deformation (strain).

  • Poisson Ratio = (axial strain) / (transverse strain) = 
  • Typical Poisson's Ratio for shafts
  • Steel = .3
  • Aluminum = .32
Polar Moment of Inertia

The moment of inertia is a measure of an object's ability to resist a change in rotational direction. The Polar Moment of Inertia is used when analyzing the ability of objects to resist torsion (or twisting) specifically.

  • The units of the Polar Moment of Inertia is or
  • Typical Polar Moment of Inertia for shafts:
    • Solid Shaft: 
    • Hollow Shaft (Tube): 
Young's Modulus of Elasticity

Young's Modulus of Elasticity is a material-specific constant that predicts how much a material is going to deform (strain) under a certain stress.

  • Young's Modulus is in the same units as stress (Newtons / square meter or Pounds / square inch)
  • Typical Young's Modulus Values for shafts:
    • Steel = 30,000,000 psi
    • Aluminum = 10,000,000 psi
Wheatstone Bridge

A wheatstone bridge is a circuit with 4 resistors connected in parallel. The bridge is "Excited" with an input voltage (Vex), and the output voltage (Vo) can be sensed to a high degree of accuracy. A typical schematic and equation relating these two voltages are shown below:

Torque Transducer

Torque transducers convert mechanical energy to electrical energy. Common examples include a load cell and a strain gage.

Torque

Torque is the measure of a twisting force that causes an object to rotate about a point. The equation is as follows:

  • Torque = Force x (Distance force applied from a point)
  • The units of torque measurement are typically Newton-meters or inch-pounds.
Power

Power is the rate in which energy is being expended (or work is being done).

  • Power = Work / Time = Force x distance / time = Force x Velocity
  • Units are typically in Watts or Horsepower
Stress

Stress is the measurement of the amount of force per area:

  • Stress = Force / Area

Alternatively, stress can be calculated using "Hooke's Law", which combines strain and modulus into the equation below:

  • Stress = Young's Modulus * Strain

The units of stress measurement are Newtons/square meter or lbs/square inch.

For a shaft, it is sometimes desired to calculate the torsional stress caused at the surface of the shaft due to an applied torque. This is found by using the following equation:

  • τ = T*R / J
    • T = Twisting moment
    • R = Radius of shaft
    • J = Polar Moment of Inertia of the shaft cross section