Figure 2. Graph of useful signal spectral density (2) and
vertical aircraft acceleration (1) [12]
As shown in Fig. 2, automatic pilot system significantly reduces the effects of
vertical acceleration at frequencies lower than 0.1 rad/s; spectral density of vertical
acceleration tends to infinity at frequencies above 0.1 rad/s. It is therefore necessary to
ensure filtering process for PG output signal with frequency of 0.1 rad/s. The most
common method of constructive implementation of this process in known gravimeters
is to use low-pass filters with a cutoff frequency of 0.1 rad/s. However, operation of
filter electronic components becomes unstable within terms of PG usage, thereby
changing its cutoff frequency. Ultimately, filter lets the interference pass to PG output
or doesn’t let the part of signal pass at all. Therefore, low-pass filter as a separate unit
of a gravimeter significantly reduces, primarily, reliability and accuracy of the device.
There is a suggestion regarding PG output signal filtering technique which consists in
creation of an element of a new gravimeter of automated AGS in the form of
piezoelectric packet, the natural oscillation frequency ω
0
of which equals to the highest
frequency of gravitational accelerations which may be measured against interference –
0.1 rad/s:
0
0.1
pp
p
SE
rads
hm
==
where m is weight of inertial mass; S
p
, E
p
and h
p
are area, material modulus of
elasticity and height of piezoelement, respectively.
It is low-frequency filtration with a cutoff frequency of 0.1 rad/s through which
can be separated from g
z
with an accuracy of 1 mGal. Besides, other components of
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