The angle of twist of a sample has been measured by attaching digital inclinometers to the two ends of a sample under torsion and calculating the difference in angle measured by the two inclinometers5. A drawing of an inclinometer from ASM is shown in Figure 1 below.
Figure 1: Digital Inclinometer Drawing11 An issue with using this instrument in the design of a mini torsion device may be its size. Depending on the design of the overall device, the radius of the inclinometer might be too large. The radius of the digital inclinometer above is 42 mm, which is about 7-8 times the diameter of the sample. A lab that used inclinometers to measure the angle of twist also found that the response of the inclinometer was sluggish5. Using a different inclinometer than the one used in the lab might correct this problem. Torsion Load Cell
Another device that could be used to calculate the angle of twist is a torsion load cell8,13. The load cell can be used to calculate the torque applied to the sample. From equation 1 below, the angle of twist can be calculated if the length of the sample, polar moment of inertia, shear modulus are known.
Equation 1: Angle of …show more content…
A potentiometer has a variable resistance that is proportional to the rotation angle12. The advantage of a potentiometer is that it can have a high resolution1. A drawing of a potentiometer from ASM is given in Figure 4.
Figure 4: Potentiometer Drawing1 A disadvantage of this instrument is that it is heavier than some other options (about 450g)1. The instrument also has a life time. The potentiometer in the figure above has a life time of 100 x 106 revolutions1.
A Data Acquisition device (DAQ) will be needed to collect data in order to calculate the angle of twist. A DAQ allows measurements to be recorded and processed by measuring signals and transferring data to a computer2. Some options of types of DAQs and setup of DAQs for this senior design project are discussed in section 3 of the tech memo.
Section 3: Data Acquisition Devices
When choosing a DAQ for a particular application, it is important to consider what types of signals need to be measured and generated, whether signal conditioning is needed, the needed sampling frequency, the desired resolution, and the amount of allowable error6. The design of the system for measuring the angle of twist and output signals of the measurement devices will determine which DAQ is appropriate for the project. Because some of the instruments discussed in Section 2 have analog outputs, it is likely that a multifunction