1. An accelerometer sensor comprising a structure having
fastened thereto a pendulum-forming inertial body
carrying a movable electrode that is connected to a
control unit that is also connected to two stationary
electrodes secured to the structure in order to co¬
operate with the movable electrode to form two capacitors
of capacitances that are variable as a function of
distances between the electrodes, the control unit being
arranged to perform operations of measuring the
capacitances and a control operation as a function of the
measured capacitances, in which a voltage is applied to
the electrodes in order to maintain the pendulum in a
predetermined position, these operations being performed
by applying pulses, the sensor being characterized in
that the control operation comprises selectively:
- a "fine" control stage in which a first voltage is applied between one of the stationary electrodes and the movable electrode, while the other stationary electrode is at the same potential as the movable electrode; or
- an "extended" control stage in which a second voltage is applied between one of the stationary electrodes and the movable electrode, the other stationary electrode being at the same potential as the movable electrode, and the second voltage being greater in absolute value than the first voltage; ; and
- in that the control stage is selected as a function of an estimate of the acceleration as obtained from the measured capacitances.
2. A sensor according to claim 1, wherein, during the
fine control stage, a reference potential is applied to
said one of the stationary electrodes, and a second
potential is applied to said movable electrode and to
said other stationary electrode, and in the extended
control stage, the reference potential is applied to said

one of the stationary electrodes and the reference potential is applied with opposite polarity both to said movable electrode and also to said other one of the stationary electrodes.
3. A sensor according to claim 2, wherein the second potential is zero.
4. A sensor according to any preceding claim, wherein the control unit comprises two digital-to-analog converters that are connected to respective ones of the stationary electrodes.
5. A sensor according to claim 4, wherein each digital-to-analog converter comprises a switch that is controlled by the control unit and that possesses a first input terminal at a reference potential, a second input terminal at a potential that is the inverse of the reference potential, a third input terminal at a zero potential, and an output terminal.
6. A sensor according to claim 5, wherein the output terminal is connected to an impedance matching circuit.
7. A sensor according to claim 1, wherein the movable
electrode (3) is connected to an input of an analog-to-
digital converter (24) having an output connected to an
input of a first estimator (6) connected to the negative
input of a subtracter (7) having an output connected to
the input of a corrector (8) having a first output
connected to a sequencer (9) and a second output
connected to a second estimator (10) having a first
output forming the main output of the control unit (5)
and a second output connected to the positive input of
the subtracter (7); the first estimator being arranged to
provide a first estimate of a movement of the pendulum
from a potential difference between the capacitances, the

second estimator being arranged to provide a second estimate of this movement and a control setpoint for compensating an offset due to static symmetry of the capacitances, the corrector being arranged to servo-control the difference between the setpoint and the first estimate on zero, the sequencer being arranged to control the sensor.
8. A sensor according to claim 7, wherein the movable
electrode (3) is connected to a first terminal of a
switch (20) having a second terminal connected to the
output of a digital-to-analog converter (11.2) connected
to one of the stationary electrodes (4.2) and to a third
terminal connected to the inverting input of a load
amplifier (21) with feedback via a capacitor (22) and a
switch (23), the load amplifier having its output
connected to the analog-to-digital converter (24)
connected to the input of the first estimator (6). '
9. A method of detecting acceleration by means of an
accelerometer sensor comprising a structure having
fastened thereto a pendulum-forming inertial body
carrying a movable electrode that is connected to a
control unit that is also connected to two stationary
electrodes secured to the structure in order to co¬
operate with the movable electrode to form two capacitors
of capacitances that are variable as a function of
distances between the electrodes, the method comprising
operations of measuring the capacitances and a control
operation as a function of the measured capacitances, in
which a voltage is applied to the electrodes in order to
maintain the pendulum in a predetermined position, these
operations being performed by applying pulses, the method
being characterized in that the control operation
comprises selectively:
- a "fine" control stage in which a first voltage is applied between one of the stationary electrodes and the

movable electrode, while the other stationary electrode is at the same potential as the movable electrode; or
- an "extended" control stage in which a second voltage is applied between one of the stationary electrodes and the movable electrode, the other stationary electrode being at the same potential as the movable electrode, and the second voltage being greater in absolute value than the first voltage; and
- in that the control stage is selected as a function of an estimate of the acceleration as obtained from the measured capacitances.