User’s Manual
14
6.6
Calibration
The calibration uses the earth’s gravity as a 1g reference signal. The calibration procedure is
completely automated and can be performed at any time. It requires the user to set the instrument in
successive stable positions with its X, Y and Z axes aligned vertically while the instrument takes the
reference measurements.
At any time the calibration can be checked by using the static acceleration measurements. The
following procedure can be used to check the calibration:
1. Place the instrument in a position where the X axis is in the vertical position and axes Y and Z
are horizontal. Read the static acceleration (Static tab in
Instrument_Manager
). If the
calibration is correct the static acceleration along the X axis should be 1g. The static
acceleration along the Y and Z axes should be 0g.
2. Place the instrument in a position where the Y axis is in the vertical position and axes X and Z
are horizontal. Measure the static acceleration. If the calibration is correct the static
acceleration along the Y axis should be 1g. The static acceleration along the X and Z axes
should be 0g.
3. Place the instrument in a position where the Z axis is in the vertical position and axes X and Y
are horizontal. Measure the static acceleration. If the calibration is correct the static
acceleration along the Z axis should be 1g. The static acceleration along the X and Y axes
should be 0g.
6.7
Scale
The records in a scale that is internal to the instrument. All data is re-scaled for display as
selected by the user, whether it is g or m/s
2
for acceleration, or m/s for velocity, dB or linear. This way
the data can be displayed in any scale irrespective of the scale selected at the time of the recording.
6.8
Inclinations
The instrument’s inclination around the X and Y axes is not measured directly. It is calculated by the
Instrument_Manager
application, from the components of the earth’s gravity along the three axes. So in
order to display inclinations, the instrument must be setup to record acceleration statistics, and at least
record the average accelerations along the X, Y and Z axes, with no high-pass filter.
After recording, the average accelerations along the X, Y and Z axes can be displayed by the
Instrument_Manager
application as individual-axis accelerations, or as inclinations.
Using the three components of acceleration along the X, Y and Z axes, the inclinations around the X
and Y axes can be calculated. These are named:
•
Tilt around the X axis:
Theta
•
Tilt around the Y axis:
Phi
Theta
and
Phi
are displayed in the
Static
tab, along with a graphical depiction of the instrument in real
time.
In addition to the inclination angles, the application calculates the norm of the acceleration. If the
instrument is stationary, and only subjected to slow changes in inclination, and is properly calibrated,
the norm of the acceleration should always be constant and equal to 1
g.