US 5,641,911 AGranted

Method and apparatus for feedback-control of an asymmetric differential pressure transducer

AssigneeVaisala Oy

InventorTapani Ryhanen

Life of this patent

Estimating the term…

Loading patent…

Abstract

The invention is related to a feedback method and apparatus for a capacitive differential pressure transducer. According to the method, a pressure-transducing conducting diaphragm (1) forming a first, moving electrode of the transducer capacitances is kept in a force balance state by means of a pulse train signal applied to a fixed electrode (2, 3). According to the invention, the diaphragm (1) is kept stationary in a geometrically constant state and a desired electric potential is applied to the diaphragm (1), the pulse train signal is applied to at least two of the fixed electrodes (2, 3), or alternatively, sets of fixed subelectrodes. The signals applied to separate electrodes (2, 3) or sets of subelectrodes are at opposite polarities referenced to the electric potential of the pressure-transducing diaphragm (1) for at least a portion of the measurement duration, and are of equal amplitude at least for each pair of electrodes (2, 3). The same pulse train signal is simultaneously used for both establishing the force balance and performing the capacitance measurement. Changes in the dielectric coefficient of the transducer fill medium are compensated for by altering the pulse amplitude, pulse width or pulse rate depending on the primary modulation method used in the feedback control.

Claims15

Dependent claims

A feedback-control method for an asymmetric capacitive differential pressure transducer having a deflectable pressure sensitive electrically conductive diaphragm, forming a first electrode of the capacitive transducer kept in a force balance state using a pulse train signal applied to fixed electrodes of the transducer, the fixed electrodes lying on one side of the pressure sensitive diaphragm, the method comprising the steps of:

keeping the deflected pressure sensitive diaphragm stationary in a fixed geometric state of deflection and applying a fixed electric potential to the pressure sensitive diaphragm;
applying the pulse train signal to at least two of the fixed electrodes or alternatively, to at least two sets of fixed subelectrodes,
the pulse train signals applied to separate ones of the at least two fixed electrodes or to separate sets of the at least two sets of subelectrodes having opposite polarities with respect to the fixed electric potential applied to the pressure sensitive diaphragm, and further wherein the pulse train signals applied to said separate fixed electrodes or to said separate sets of subelectrodes are of equal amplitude at least for each pair of said at least two electrodes or of said at least two sets of subelectrodes;
changing a duty cycle of the pulse train signal so as to control a geometric state of deflection of the pressure sensitive diaphragm;
and
measuring, based upon a duty cycle of the pulse train signal, a difference in capacitance between capacitances respectively formed between the pressure sensitive diaphragm and said at least two fixed electrodes, or formed between the pressure sensitive diaphragm and said at least two sets of fixed subelectrodes, such that the same pulse train signal is simultaneously used for controlling the geometric state of deflection of the pressure sensitive diaphragm and for performing the capacitance measurement.

3 more elements

Dependencies are inferred from the claim text.