Copyright © Sigicom AB 2019
19
3.
Measuring Parts of the System
3.1.
Measuring Hardware
3.1.1.
Vibration Sensor
As sensing elements, the C12 uses three geophones with lower frequency
response down to 4.5 Hz. The low frequency resonance of each geophone
is electrically dampened, and its characteristics are measured at calibration
and saved in the calibration memory. These data is later used as input data
for the digital frequency compensation used in some of the measurement
standards.
3.1.2.
Analog Electronics
An adjustable amplifier amplifies the geophone signal according to the
selected measurement standard. The signal is then low-pass filtered with
an analog filter to avoid aliasing. After that the signal passes an analog-
digital converter and all subsequent signal processing is digital.
3.1.3.
Analog-Digital Conversion
All sampling is performed at 4096 Hz and signal frequencies up to 500 Hz
are included. The analog-digital converter has 16 bits resolution which, at
measurements up to 250 mm/s, gives a smallest conversion step of at least
0.01 mm/s, and presentation of interval values is set to a resolution of 0.05
mm/s.
3.1.4.
Digital Signal Processing
A digital signal processor (DSP) filters, compensates and detects the
signals according to the selected measurement standard. Every geophone
is regarded as an individual, and an adjustment is made with respect to the
characteristics of that specific geophone. This gives measurements of high
quality.
