20
6. Combining equations 4 and 5 gives:
7. Substituting the given values for
, g and
yields:
8. On channel 'A', which displays the period of vibration, T, multiplied by a factor of 106;
9. Combining equations 7 and 8 gives:
10. Equation 9 must now be expressed in terms of the strain in the surface of the body to
which the gage is attached. Since the deformation of the body must equal the deformation
of the wire:
Where;
is the strain in the body.
Lg is the gage length (in inches).
11. Combining equations 9 and 10 gives:
Where; (for the Model 4000 Strain Gage)
Lw is 6.250 inches.
Lg is 5.875 inches.
12.
Therefore:
(Note that T is in seconds x 106 and
ε
is in inches per inch)
13. The display on position "C" of the GK-401/403 Readout is based on the equation:
Note that in this formula
ε
is in micro inches per inch and T is in seconds x 106
Alternatively
ε
= 4.062 x 10-3 f 2 microstrain. Where f is the frequency in Hz
The squaring, inverting and multiplication by the factor, 4.062
109, is all done internally by
the microprocessor so that the displayed reading on Channel C is given in terms of
microinches/inch (
).
f
L
g
w
w
1
2
f
L
w
w
101142
T
f
10
6
w
w
L
T
97 75
2
2
.
w
w
g
L
L
97 75
2
3
.
T
L
L
w
g
4 062 10
1
3
2
.
T
4 062 10
1
9
2
.
T
