
Sensors in Engineering and Science 33
ions, λ is the average distance traveled by an electron between collisions, and
N
0
is the total number of conducting electrons. Equation 2.15 implies that
the differential resistance change and, thus, the gage factor, is independent of
the material properties of the conductor. This also implies that the change
in resistance only will be proportional to the strain when the sum of the
differential changes on the right hand side of Equation 2.15 is either zero or
directly proportional to the strain. Fortunately, most strain gage materials
have this behavior. So, when a strain gage is used in a circuit such as a
Wheatstone ...