View source for Projects:2020s1-2511 Small-Scale Torque Gauge

== Introduction ==

In order to estimate mechanical power delivered by a rotating machine, it is necessary to measure two variables, torque (T) and angular velocity (omega). Angular velocity is typically measured using an encoding wheel. Commercial torque gauges are typically very expensive and operate over a range that is too large for small desktop projects. In this project, we will construct a small torque gauge that is based on a spaceframe (3D-truss) together with commercially available strain gauges.

== Project Team ==

=== Supervisors ===

*Dr. Andrew Allison
*Dr. Derek Abbott

=== Students ===
*Bohan Liu
*Weixi Tao

== Background ==

This project aims to construct a small-scale torque gauge that is based on a spaceframe (3D-truss) together with commercially available strain gauges. Strain gauge that converts applied force or torque into a change in electrical resistance. Using strain gauges to build a strain gauge load cell to measure the torque. That has a lower cost and can be used in small desktop projects. The initial test of concept would involve the measurement of a three-phase permanent magnet machine over a range of operating conditions. In principle, this apparatus could measure dynamic time-dependent torque, as well as steady-state torque. Besides, the torque gauge could be used to measure a range of different machines for future projects and can be used as a teaching aid demonstration in the experimental class.

=== Technical Background ===

==== Strain Gauge ====
The strain gauge is the essential component of small-scale torque gauge. It is a device used to measure the strain on an object or stresses generated by[[File:Wire Lead Strain Gauge 4mm.png|thumb|caption]] machinery. The general strain gauge consists of insulating flexible backing, which embeds different size metallic foil pattern [1]. A strain gauge takes advantage of the physical property of electrical conductance. Metallic foil would deform as the object deforms, causing the change of strain gauge electrical resistance. When measuring, ensure that the gauge is stretched or compressed within the limits of its elasticity without breaking or permanent deformation. When the gauge is stretched, the metallic foil will become longer and thinner and increase the strain gauge's electrical resistance. On the contrary, when the gauge is compressed, the metallic foil will become shorten and broaden and decrease the electrical resistance of strain gauge [2]. By accurately measuring the change of strain gauge resistance, the magnitude of the induced force on the object can be inferred. 
The resistance of a standard strain gauge ranges from 30Ω to 3000Ω. When measuring under the elastic limit of the given gauge material, the resistance of strain gauge may change only one percent. If more force is applied to cause a more significant resistance change, it may cause permanent deformation of the metallic foil and damage the strain gauge. Thus, in order to apply gauge to actual measurement, it is necessary to measure extremely small changes in resistance with high accuracy.

==== Load Cell ====
The Wheatstone bridge circuit is using two series-parallel arrangements of resistances connected between a voltage supply terminal and ground producing zero voltage difference between the two parallel branches when balanced. The output voltage can be calculated by formula: