How strong is an airplane? Will it be able to survive the stresses expected during landing, take-off and during rough weather? With all of the advances recently in computer-aided design and stress calculation, the best way to prove that an aircraft is sufficiently robust is to test the assembled airframe. Testing consists of placing the airframe in a large fixture and applying force at several points using hydraulic jacks. The resulting stresses must be measured directly and compared to the allowable limits.

To measure the stress in an airframe, a large number of strain gages are placed at critical points on the structure and their output recorded as force is applied. The strain gage is carefully bonded to the structure with a special epoxy so that as the structure changes its shape slightly under load, the strain gage will change its resistance very slightly. The resistance of the strain gage must be measured very precisely so that the stress levels in the airframe can be determined.

To accurately measure the changing resistance of strain gages attached to the airframe requires a signal conditioner that can supply precision excitation, allow for bridge completion, accept lead-wire compensation and provide sufficient gain for a high-level output for data acquisition systems Such systems consists of up to several hundred channels and the signal conditioning must be rack-mounted and compact.