Appendix B Test Overview Io
SENSOR
102
SMT-200 Operations and Technical Manual 2.00/R1
B.12 Damping Calculations
It may be necessary at some stage to modify a geophone to achieve a particular level of damping. The
following calculations will assist in achieving the correct damping.
Damping constant, RtBcFn, is given by :
m
Go
RtBcFn
π
4
2
=
Example..
SM-4 10 Hz 375 to achieve 0.70 damping
6000
011.04
8.28
2
=
×
=
π
RtBcFn Ω Hz
Bc Bt Bo=− = − =070 025 045.. .
Rt
RtBcFo
BcFo
==
×
=
6000
045 10
1333
.
Ω
Rs Rt Rc=−= − =1333 375 958 Ω
The nearest value of resistor to this is 1 KΩ. Recalculating with this value the damping for this
element turns out to be 0.69.
B.13 Temperature Compensation
Temperature compensation that is done either on the specs themselves or the recorded data will be
calculated as follows:
)(004.0 TspectRsRsRt
−+=
Rt
= Resistance at temperature t
Rs = Resistance at 20 ºC
)(002.0 TspectBsBsBt
−−=
Bs = Damping at 20 ºC
Bt
= Damping at temperature t
Gt Gs=
Gt
= Sensitivity at temperature t
Gs = Sensitivity at 20 ºC
t
= Temperature
Tspec
= Geophone temperature spec.
Rt = Total geophone resistance
Rc = Coil resistance
Rs = Shunt resistance
Bt = Total damping
Bc = Coil damping
B
0
= Open circuit damping
Fn
= Natural Frequency
G
0
= Open circuit sensitivity
m = Suspended mass
From Spec sheet:
Bo = 0.25
Go = 28.8 V/m/s
Fn = 10 Hz
m = 11 grams
π = 3.142
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