Minimate Pro Operator Manual 9–31
geophones and measures the response. If the geophone‟s response falls within a
specified range, the monitoring operations can continue. If the geophone‟s
response does not fall within a specified calibration range, the geophone is not
setup or functioning properly. You cannot record Events until you fix or replace
the geophones.
Natural Frequency
Waveform measurements check the natural frequency (or period [t]) of a
geophone‟s sensor coil assembly. Referring to the figure below, the distance
from P
1
to P
2
represents 0.125 seconds. Since Frequency is the reciprocal of the
period, F=1/t, the frequency is approximately 8 Hz. A calibrated sensor has a
natural frequency between 6.5 and 9.5 Hertz. Calculations for all geophones
appear with each recorded Event.
Calculating
the Natural
Frequency of a
Geophone
Damping – Overswing Ratio (OR)
The OR measures damping and is calculated by computing the ratio of the
magnitude of adjacent waveform peaks according to the following formula:
Acceptable OR ranges from 2.8 to 4.8. The figure below displays a graph of a
geophone coil‟s "free fall" response. A
1
and A
2
are used for OR calculations.
Calculating
the Overswing
Ratio of a
Geophone
(1)2. Sensor Check Overview – Microphones
Sensor Check tests the microphone operation by sending a signal to the
microphone and measuring its frequency and amplitude response. If the results
of the test fall within specified ranges, the microphone is within calibration.
b. Measurement System:
The unit uses the Metric or the Imperial measurement system. Event Reports and
displayed results will be shown in the selected units. To set the unit to operate with either
system, follow the directions below.
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General