Strain gauge data logger for educational purposes

For many years Strength of Materials laboratories in undergraduate engineering instruction have been taught using massive testing machines, and large specimens with their accompanying large loads. Such machines are obviously expensive and subject to damage. For this reason it has been traditional to conduct such experiments for undergraduate students on a demonstration basis, where the instructor actually operates the equipment, and the students stand by observing and taking notes. This type of system was prevalent up until a few years ago and probably had some justification when strain measuring equipment was in its infancy, and had to be carefully adjusted by hand by people with years of experience in order to obtain consistently reliable results. Almost all industrial strain measurement is now carried out by the use of resistance strain gauges, and these have become inexpensive enough so that students may themselves attach their own strain gauges for educational purposes, thus gaining invaluable practical insight into the difficulties associated with such types of measurements. However, instrumentation for the reading of strain has historically been very expensive and not readily available for undergraduate, individual, educational purposes. Recently the cost of electronic components has been reduced significantly in the United States by volume production of items which in some cases can be adapted to strain indicating equipment. This opens up the possibility of relatively inexpensive strain measuring instruments being available for instructional and general laboratory use. A description of one such instrument is the subject of this present paper.