Chapter 5
5–8
BlastMate III Operator Manual
5.3.2. Checking the Microphone
Sensorcheck tests the microphone’s 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.
5.3.3. Sensorcheck Report
The Sensorcheck report appears on the BlastMate III display. The message “All Channels
Working, Press Print to Print” indicates the BlastMate III sensors have passed the Sensorcheck.
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 BlastMate III 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 BlastMate III calculates the Peak Particle Velocity, Zero Crossing Frequency, Peak
Acceleration, and Peak Displacement for each of the transverse, vertical, and longitudinal axes.
The BlastMate III 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 BlastMate III calculates the PPV for each geophone.
Peak Particle Velocity
Time
(seconds)
Amplitude
(In/s or mm/s)
Figure 5.9 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 BlastMate III measures
between zero crossings. Frequency is the number of periods that occur in one second calculated
by the formula: Frequency = 1/period.
Summary of Contents for Blastmate III
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