Copyright © Sigicom AB 2021
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3.
Measuring Parts
3.1.
Measuring Hardware
3.1.1.
Vibration Sensor
The C22 uses three geophones with low frequency responses down to 4.5
Hz. The low frequency resonance of the geophones is electrically
dampened, and their characteristics are measured during calibration and
saved in the instrument’s calibration memory. This data is later used as
input for the digital frequency compensation used in some measurement
standards.
3.1.2.
Analog Electronics
An adjustable amplifier enhances the geophone signal according to the
selected measurement standard. The signal is then low pass filtered with
an analog filter to avoid aliasing. Then the signal passes through an
analog-digital converter and all subsequent signal processing is digital.
3.1.3.
Analog-Digital Conversion
All sampling is performed at 4096 Hz. The analog-digital converter has a
16 bits resolution which, at measurements up to 250 mm/s (10 in/s) in the
largest range, provides a minimum resolution of 0.01 mm/s (0.0004 in/s).
In the display, the resolution of interval values is set to 0.05 mm/s (0.002
in/s) in this range.
3.1.4.
Digital Signal Processing
The main processor of the C22 is a combined general processor and a
digital signal processor (DSP). The DSP part of the processor filters,
compensates and detects the signals according to the selected
measurement standard
