Question

The following quesiton pertains to a strain gauge on a cantilever beam often used in labs.

Are there any advantages in placing a strain gauge at one point on the beam as opposed to another? In general, what should the criteria be for choosing locations for strain gauges? Consider where on the beam the strain will be of highest amplitude or of highest frequency. What do you want (i.e. what criteria is most important)?

In order to get the most accurate readings, should a strain gauge have a high stiffness or a low stiffness? Explain.

Answer 1

when strain gauge is placed at a point where the strain ( displac ement) is the maximum, the strain measured by the strain gauge is the one with least relative error
as relative error depends on the least count(which will remain consgtant) and the actual strain, so when actual strain is large, relative error decreases for a constant least count

also, the strain gauge does not need to have osscilations in strain as this will create more error due to hysterisis
hence
on a beam, maximum deflection is near the location where maximum load ie being applied
hence on a beam the straingauge should be placed on principal axis where the strain is largest and there is no frequency iof osscilation

for having more accurate readings, a strain gauge with low stiffness will strech more but the least ciunt of the scale measuring this displacement will be the same
hence
more change in length means lower relative error, hence low stiffness strain gauge must be used