For axial strain measurement on a bolt, or cylindrical shaft, four strain gages are bonded to the shaft - two gages along the axis of the shaft at diametrically opposite points, and two gages along the circumferential direction, again at diametrically opposite points.
The axial gages will be in tension, and the circumferential gages will be in compression due to Poisson effect.
The gages are interconnected so that the tension gages have compression gages adjacent to them, and the output of the bridge should be divided by 2.6 to get the strain on the shank of the bolt,
The model P3 strain indicator has the facility to do the scaling automatically.
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