perturbations with predominant frequency of more than 0.1 rad/s are also removed
from PG output signal. These perturbations includes translational vibration
acceleration with predominant frequency of 3140 rad/s; angular accelerations with
predominant frequency of more than 0.1 rad/s [10–12].
Three-axis preselectric sensor. Existing gravimeters measure only the gravity g
z
along the vertical axis Oz, what are the components of gravity g
x
and g
y
along the axes
Ox and Oy are equal to zero because of their small size [11]. However, to achieve the
accuracy of measurement of gravity high for 1 mGal, the above components must be
taken into account. For example, if g
x
=g
y
=0,9 mGal [12], then the module of these
accelerations will be equal to:
mGal
27
,
1
9
,
0
2
2
2
2
=
=
+
=
y
x
хy
g
g
g
As you can see, the neglect of g
x
and g
y
leads to the emergence of significant
errors, which is unacceptable.
Improving the accuracy of measurement in three-axis low-frequency gravimeter
is assured by the fact that for each measurement axis Oz and Ox, Oy, the gravity is
mounted the sensing element Az, Ax, Ay, done with two channels, each with one
equipped by piezoelectric elements that are identical (Fig. 3). Inertial mass is attached
to the bottom of piezoelectric element one channel and to the top of piezoelectric
element of the second channel. The piezoelectric element of the first channel of each
sensing element operates on the basis of tensile deformation, and the piezoelectric
element of the second channel – compressing deformation.
Piezoelectric elements have a natural frequency equal to the frequency of
intersection of the spectral density of the useful signal of gravity signal and a primary
interference of the vertical acceleration of the aircraft.
Output electrical signals of the piezoelectric elements both channels all sensing
elements are received at the inputs of operational amplifiers that, in addition to
strengthen perform and function the summation of the signals from the inputs of
BCOM.
In BCOM will be carried out the necessary calculations to determine the value of
the full vector
g
and the module
g
of the gravity.
So, by using three sensing elements Az, Ax, Ay it is possible to measure the
complete vector of gravityg
:
z
y
x
g
g
g
g
+
+
=
and not just one component
z
g
, as in
the prototype.
In new sensor what is offered at each axis measurement set the sensing element is
made with two channels, each with piezoelectric element 1 and 2 along the axis Oz, 3
and 4 along the axis Ox, 5 and 6 on the axis Oy.
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