I recently did a bending lab with a WB Strain Gauge in a bunch of different configurations.
One measurement in particular is bothering me. Referring to the figure below, there are four strain gauges, Yellow, Orange, Black and Red mounted to a cantilevered beam with an applied loading 'P.'
I had the data acquisition system output a measurement for a Half-Bridge configuration in which R1 = RYellow and R2 = ROrange
We can see from the figure that both of the gauges are in tension. So why is the strain measurement that I got negative? It is effectively taking the strain measured from the yellow gauge and subtracting it from the strain ,measured from the orange gauge. Why does it do that? What exactly is this quantifying?
Also: I thought maybe I screwed this up, but the Lab Assistant had all of the 'approximate expected strains' and mine matched up pretty well.