Question

Hello for a laboratory experiment we used strain gauges to measure the internal pressure of a coke can. Our instructor told us one of the sources of error would be not aligning the gauges perfectly. Why would this cause error in the experiment? Is there any other sources of error as well.

Answer 1

Yes, misalignment of strain gauges is a big source of error in the strain measurements. For this understand how strain gauge measures strain So it is a kind of sensor which we attach to a material at which the external application of force is there and subsequent measurement of strain is there but inside this the attachment of guage to material is important as the strain axis through which strain we are measuring is principal axis. A misalignment always cause the axis to rotate by a very small angle hence the angle between the maximum principal strain axis and the intended axis of strain measurement gets change and results in very high strain value errors.

Other sources of error :

a) Strain sensing error : It is due to improper bond between the material and the strain guage.

b) Local sources of error : error due to change in local conditions example Temperature. Large changes in temperatures in both the test part and the strain gage can adversely affect the accuracy of the strain measurement.

c) Instrumental errors : errors due to malfunctioning of instrument. These errors should be negligible unless the instrument is actually malfunctioning.