Instantel 716A0401, Operator'S Manual

Page: 59 / 86

Reference
MiniMate Plus Operator Manual
5–9
5.4. Anti-alias Filters
Aliasing occurs when a high–frequency signal appears as an erroneous low frequency because the
waveform was sampled at too low a sampling rate. An anti-aliasing filter solves this problem by
removing the high–frequencies.
5.5. Data Analysis Techniques
The following sections define the MiniMate Plus data analysis techniques. The first section,
ground vibrations, discusses calculations applied to event data recorded by a transducer. The
second section, sound pressure, describes the microphone event data calculations.
5.5.1. Ground Vibrations
The MiniMate Plus calculates the Peak Particle Velocity, Zero Crossing Frequency, Peak
Acceleration, and Peak Displacement for each of the, transverse, vertical, and longitudinal axes.
The MiniMate Plus calculates Peak Vector Sum using data from all three axes.
a. Peak Particle Velocity (PPV)
Peak Particle Velocity indicates the maximum speed particles travel resulting from an event’s
ground vibrations. The MiniMate Plus calculates the PPV for each geophone.
Figure 5.11 Calculating Peak Particle Velocity.
b. Zero Crossing Frequency (ZC Freq)
The Zero Crossing Frequency calculates the event waveform’s frequency at the largest peak.
(1) Calculating Zero Crossing Frequency
To calculate the Zero Crossing Frequency, we need to determine the period of oscillation of the
waveform. Convenient waveform positions for measuring period, the time for one complete cycle,
occur between two successive peaks, troughs, or zero crossings. The MiniMate Plus measures
between zero crossings. Frequency is the number of periods that occur in one second calculated
by the formula: Frequency = 1/period.