Capacitive transducers
First Claim
1. A circuit for providing outputs from at least two capacitive transducers, the circuit comprising:
- respective means for each transducer for feeding an alternating input signal thereto;
common means for receiving the signals thereby produced from the transducers; and
respective means for each transducer for receiving the output signal from said common means and demodulating the received signal synchronously with the frequency of the respective input signal to that transducer;
wherein the frequencies of said input signals are different from each other.
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Accused Products
Abstract
A signal conditioning circuit for multiple channel capacitive displacement transducers. The transducer 30 comprises three differential capacitive transducers, driven by respective square waves from modulators 32x, 32y, 32z. The modulators are driven at different frequencies which are even multiples of each other, derived from a divider 68. The signals from each differential capacitance pair of the transducer 30 are received by a common charge amplifier 48. They are then demodulated by respective phase sensitive rectifiers 50x, 50y, 50z, each of which is driven at the same frequency as the corresponding modulator. The outputs of the phase sensitive rectifiers are integrated, e.g. by circuits 60,62,44 for one of the channels, and the resulting voltage signal is fed back to the corresponding modulator so as to tend to null the input to the charge amplifier 48. The use of modulating frequencies which are even multiples of each other enables the signals to be multiplexed through a single charge amplifier 48. The mechanical construction of the multi-channel transducer 30 is also described.
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Citations
12 Claims
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1. A circuit for providing outputs from at least two capacitive transducers, the circuit comprising:
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respective means for each transducer for feeding an alternating input signal thereto; common means for receiving the signals thereby produced from the transducers; and respective means for each transducer for receiving the output signal from said common means and demodulating the received signal synchronously with the frequency of the respective input signal to that transducer; wherein the frequencies of said input signals are different from each other. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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9. A device which is responsive to displacement in at least two axes, the device comprising a differential capacitive displacement transducer for each said axis,
each transducer including at least two opposed outer capacitor electrodes, and a central electrode which is relatively movable in said at least two axes between the two outer electrodes, the central electrode of each transducer being common with the central electrode of the or each other transducer.
Specification