Sensor SMT-200 Operation And Technical Manual page 76

Section 5 Geophone Testing
5.4 Basic Geophone Troubleshooting using the continuous impedance test
It is recommended to first set aside defective strings and to fault find later. Once a defective string has
been found the problem has to be further isolated. Most faults tend to be due to damaged cable.
These are normally fairly easy to find. However some faults are more subtle. The best tool for finding
these problems is the continuous impedance test.
For example say a particular geophone string failed the tests described in Section 5.2 with low
sensitivity. This could indicate an out of spec element. To check for this set the test sequence menu as
follows:
Tests Sequence
----------------
1 Low Drive off
2 Polarity off
3 Noise off
4 Leakage off
5 Resistance off
6 Fn, Bo, Go off
7 Dist, Imp off
8>Cont Imp ON
9 Polarity Last
0 Back to Setup
----------------
Select
Low Drive Test
--Test results--
No. 10
Temp 24.2
Imp 2112 ohm
<2069> <2153>>
+/- New Ref
Now Testing
Cont Imp....
66
This will activate the continuous impedance test when the next test is run.
The bar-range will specify how sensitive the scale is and this can be set in
the Limits menu [2-5-5].
•
Invert all the geophones except for the first geophone in the string.
The geophones are inverted to prevent movement of the coil. The
bottom spring of a vertical phone is stronger than the top one to
counteract the effect of gravity. By inverting the element or placing it
on it's side the bottom spring clamps the coil to the top of the case.
This will not work with horizontal phones or phones with a natural
frequency above 14 Hz.
• Run the test. The first measurement will establish a reference
impedance. (The actual value is not important it can take any range
o
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of values, there is no right or wrong value in this case).
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SMT-200 Operations and Technical Manual 2.00/R1
SENSOR