Appendix B Test Overview
Io
SENSOR
100
SMT-200 Operations and Technical Manual 2.00/R1
B.8
Distortion test drive mode
Velocity plot
Excursion plot
* Historical test frequency
Constant velocity mode
At constant velocity the distortion test drive level is fixed at 0.7 in/s ( 0.01778 m/s). The actual excursion that
this produces will depend on the frequency of the drive signal and the geophone’s natural frequency. Lower
drive frequencies will result in a proportional increase in the moving mass excursion. This increased
movement could result in increased distortion value due to the geophone springs being driven into a non
linear region.
Constant excursion mode
At constant excursion the test drive current (and so the drive level) is compensated to allow for testing at
frequencies other than 12 Hz. By altering the drive level the excursion of the moving mass can be maintained
at 0.236 mm, which is the same value as would have been produced driving the moving mass at 12 Hz with
a 0.7 in/s drive. Thereby giving consistent results regardless of the distortion test frequency.
B.9 Continuous
Impedance
Continuous impedance is somewhat like a resistance test but instead of a DC current an AC current at
the geophones natural frequency is fed to the coil continually while the phone is under test. The coil
will then oscillate as it is excited by the applied current. A coil that is stuck or moving abnormally will
produce a different result than a freely moving coil. This facility makes this an excellent trouble-
shooting test.
B.10
Low Drive Continuous Impedance
The low drive continuous impedance test applies a user defined low drive (default 10% of the nominal
drive level) to the geophone string under test so that sticking or dragging coils can be found whereby if
a higher drive level was used the coil would be freed.
12Hz
*
Frequency
Ex
cu
rs
io
n
Constant Velocity
Constant Excursion
12Hz
*
Frequency
Ve
lo
ci
ty
Constant Velocity
Constant Excursion
0.7inch per sec.
