Device for measuring a force with the aid of a capacitative sensor using charge transfer
First Claim
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1. A device for measuring an inertial force corresponding to an acceleration, comprising:
- a capacitive sensor (1) including two capacitors (C1, C2) and first, second and third connection means, a first plate (2) of each of said capacitors being linked electrically to the first connection means, and second plates (2a, 2b) of said capacitors being linked respectively to said second and third connection means, said first plate (2) of at least one of said capacitors furthermore including an elastically suspended movable flap and being able to be subjected to said force in such a way as to vary the capacitance of at least one of said capacitors (C1, C2) and,an interface circuit (5, 7, 9A,
12) linked to said capacitive sensor (1) so as to deliver an output potential (Vm) representative of said force and comprising;
integration means (5) responding to electric charge at the input thereof so as to generate, between the output (4) thereof and a source of reference potential (dc), said output potential (Vm) with a value proportional to the total quantity of said electric charge at the input;
means (Cph) for delivering at least one periodic control signal (Ph1, Ph2) exhibiting in succession a first measuring state and a second charge transfer state;
switchable linking means (7) responding to said first state of the control signal so as to bring said second plates (2a, 2b) respectively to a first potential (V0) and to a second potential (-V0) symmetric with said first potential (V0) with respect to said reference potential (dc), and also responding to said second state of the control signal so as to bring said second plates (2a, 2b) to the potential of said output (4) of the integration means (5); and
charge transfer means (9A) including charge accumulation means (C3) which, during one (Ph1) of said states of said control signal, transfers to said integration means (5) a quantity of charge representative of the charge present on said first plate (2), and which, during the other (Ph2) of the states of said control signal, is made to discard the charge which it had accumulated previously;
whereinthe state during which the charge accumulation means (C3) is made to discard said charge is the first measuring state (Ph1) of the control signal, and whereinsaid charge transfer means (9A) also comprises means (C4, 15-1 to 15-4) for reversing the sign of said quantity of charge when the latter is transferred to said integration means (5).
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Abstract
There is described a device for delivering an output signal representative of a force by means of a capacitative sensor (1) and of an interface (5, 7, 9A, 12) for transferring charge accumulated on the capacitor (C1 and C2) of the sensor. In order to reduce the influences of the stray resistances impairing the operation of the sensor (1), the capacitors of the latter are precharged during a first operating phase, whereas during a second operating phase this charge is transferred, while the two capacitors of the sensor (1) are short-circuited and brought to the output potential of the interface.
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4 Claims
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1. A device for measuring an inertial force corresponding to an acceleration, comprising:
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a capacitive sensor (1) including two capacitors (C1, C2) and first, second and third connection means, a first plate (2) of each of said capacitors being linked electrically to the first connection means, and second plates (2a, 2b) of said capacitors being linked respectively to said second and third connection means, said first plate (2) of at least one of said capacitors furthermore including an elastically suspended movable flap and being able to be subjected to said force in such a way as to vary the capacitance of at least one of said capacitors (C1, C2) and, an interface circuit (5, 7, 9A,
12) linked to said capacitive sensor (1) so as to deliver an output potential (Vm) representative of said force and comprising;integration means (5) responding to electric charge at the input thereof so as to generate, between the output (4) thereof and a source of reference potential (dc), said output potential (Vm) with a value proportional to the total quantity of said electric charge at the input; means (Cph) for delivering at least one periodic control signal (Ph1, Ph2) exhibiting in succession a first measuring state and a second charge transfer state; switchable linking means (7) responding to said first state of the control signal so as to bring said second plates (2a, 2b) respectively to a first potential (V0) and to a second potential (-V0) symmetric with said first potential (V0) with respect to said reference potential (dc), and also responding to said second state of the control signal so as to bring said second plates (2a, 2b) to the potential of said output (4) of the integration means (5); and charge transfer means (9A) including charge accumulation means (C3) which, during one (Ph1) of said states of said control signal, transfers to said integration means (5) a quantity of charge representative of the charge present on said first plate (2), and which, during the other (Ph2) of the states of said control signal, is made to discard the charge which it had accumulated previously;
whereinthe state during which the charge accumulation means (C3) is made to discard said charge is the first measuring state (Ph1) of the control signal, and wherein said charge transfer means (9A) also comprises means (C4, 15-1 to 15-4) for reversing the sign of said quantity of charge when the latter is transferred to said integration means (5). - View Dependent Claims (2, 3, 4)
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Specification