quantities without device re-turning; frequency-modulated output signal. But string
gravimeters have demerits too. There are large systematic errors under conditions of
airplane vibration; sharp neglecting reboundes, which are connected with resonance of
separate pick up components, are observed with some vibration frequencies; large
dynamic temperature factor conditioned by vertical convective flows; gravimeters are
subjected to barometry effect that is phenomenon connected with deformation of
dampening liquid vessel sides under atmosphere pressure action.
Table 1 Technical characteristics of different types of gravimeters
Gravimeter
Drift
over
12h,
mGl
Sensi-
tivity
thershold,
10
-1
, mGl
mass,
kg
Dimensions
10
-z
, m
Pendulu-
mity,
10
-5
,
kg∙m
Special
requi-
rements
Bell (BGM-2, VM-IX)
2
2
2.24
10x15x20
-
-
Autonetics (VM-7G)
3
2
-
-
24
-
Arma (D4E)
2
1
-
23x23
-
TK
Arma (LotD)
2
1
-
7x13
-
TK
PIGA (PIGA-25)
1
1
1.7
13x15
25
AS
GAL-S
2
2
10
30x30x74
-
TK
GSD
1
1
3-6
5.2x7
-
TK
TK - temperature control; AS - azimuth stabi1ization.
Devices of gyroscopic linear acceleration integrator type (PIGA-16, PIGA-25) are
considered the most perspective to utilize as AGS gravimeters in the result of carried
out in the USA researches because they have a number of important advantages over
another gravimeters. Here are some of them. Stability of PIGA gravimeter readings is
defined by gyro rotor angular momentum constancy, which is defined by stability of
supply voltage frequency in the main. Ensuring of angular momentum constancy is less
complicated then to ensure constancy of number of parameters defining operation
stability of other devices types represented in the table 1. PIGA gravimeter has wide
measurement range. Feedback application in the device enables to obtain zero
constancy. Friction in the pendulum rotation axle is reduced to minimum. This ensures
high device sensitivity to the object linear acceleration. But PIGA type device performs
integration of useful signal. Its output signal in the form of angular velocity of gravity
acceleration. This gravimeter needs application of gyro turn angular velocity
measurement gear, which differs by small clearances, not large reverse action moment,
low threshold sensitivity, wide range of measuring velocities. But realization of such
gears is complicated technical task and can be achieved by the way of price increase
and reliability reduces as a rule. Besides that, this gravimeter has one sensitivity axis,
which is parallel to the gyro rotation axis with respect to the basis, and measures
gravimetric acceleration projection on this axis. It's demanded accuracy stabi1ization
- 1578 -