3.10 Vibration Measuring Seismic Instruments
89
Fig. 3.18 Variation of μ
with η
3.10.3 Discussion About the Instruments
Let η = 1, φ = 90
◦ . Substituting these values in Eq. (3.65), it becomes
z =
my 0 ω
2
k2η ζ
cos ω t
(3.72)
or
z =
ω y 0
2 pζ
cos ω t
Differentiating Eq. (3.69) with respect to t, we get
˙
y = y 0 ω cos ω t
(3.73)
Combining Eqs. (3.72) and (3.73), we get
z =
˙
y
2 pζ
(3.74)
The relative displacement in this case is proportional to the relative velocity.
However, as the range of frequencies of this system is very small, this principle is
never used for the measurement of velocities of the vibrating body.
The relative displacement which is to be measured is converted into electrical
pulse. The motion to be measured is detected by a transducer. The base of the
transducers is firmly attached to the body, whose motion is to be measured. The
input acceleration or displacement is usually converted into voltage. Output from the
transducer passes on to an amplifier, where the value gets modified. It is then passed
on to an oscilloscope for necessary display.