Method for correcting the drift offset of a transducer
First Claim
1. A method for correcting the drift offset of a transducer having an analog output signal corresponding to the sensed pressure of a flow in either direction through a flow path, comprising:
- (a) providing an analog to digital converter having a defined range of digital counts and identifying a base digital count value of the digital range corresponding to the base zero flow in either direction;
(b) converting the transducer output signal to a digital value at a given sampling rate;
(c) identifying a zero-flow condition through the flow path when the converted transducer voltage signal does not vary more than a selected number of digital counts over a first period of time;
(d) determining a count offset value based on the difference between the identified base digital count value and the digital count output of the analog to digital converter during an identified zero-flow condition;
(e) adjusting the output of the analog to digital converter following the identified zero flow condition by the determined offset value;
(f) maintaining a buffer containing a selected number of digital values acquired last in time;
(g) adding to the buffer each digital value converted from a sampled voltage signal and subtracting from the buffer the oldest digital value for each new value added;
(h) determining the difference between the maximum and minimum values in the buffer; and
(i) determining that a zero-flow condition exists when the determined difference is less than a second selected number of digital counts.
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Accused Products
Abstract
A method for correcting the drift offset of a transducer is disclosed which method is used in connection with a portable, battery-powered, hand-held system for releasing a controlled dose of aerosol medication for inhalation by a patient. The device includes a durable body and a medication cassette inserted in the durable body. The body includes a flow sensor having an asymmetrical orifice that is calibrated, independent of the cassette, to convert the sensed pressure due to flow into a flow rate. The orifice is separately calibrated for an inhalation flow rate range and an exhalation flow rate range over a selected number of known flow rates. The sensed pressure value is corrected for transducer offset drift and converted to a flow rate using the calibration data and piecewise linear interpolation.
180 Citations
13 Claims
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1. A method for correcting the drift offset of a transducer having an analog output signal corresponding to the sensed pressure of a flow in either direction through a flow path, comprising:
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(a) providing an analog to digital converter having a defined range of digital counts and identifying a base digital count value of the digital range corresponding to the base zero flow in either direction; (b) converting the transducer output signal to a digital value at a given sampling rate; (c) identifying a zero-flow condition through the flow path when the converted transducer voltage signal does not vary more than a selected number of digital counts over a first period of time; (d) determining a count offset value based on the difference between the identified base digital count value and the digital count output of the analog to digital converter during an identified zero-flow condition; (e) adjusting the output of the analog to digital converter following the identified zero flow condition by the determined offset value; (f) maintaining a buffer containing a selected number of digital values acquired last in time; (g) adding to the buffer each digital value converted from a sampled voltage signal and subtracting from the buffer the oldest digital value for each new value added; (h) determining the difference between the maximum and minimum values in the buffer; and (i) determining that a zero-flow condition exists when the determined difference is less than a second selected number of digital counts. - View Dependent Claims (2, 3, 4, 5, 6, 7)
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8. Apparatus for correcting the drift offset of a transducer having an analog output signal corresponding to the sensed pressure of a flow in either direction through a flow path, comprising:
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an analog to digital converter having a defined range of digital counts and a digital value in the digital range corresponding to the base zero flow in either direction; means for controlling the analog to digital converter to convert the transducer output signal to digital value at a given sampling rate; means for identifying a zero-flow condition through the flow path when the digital values do not vary more than a selected number of digital counts over a first period of time; first means for determining an offset value based on the difference between the identified base digital count and the digital value output of the analog to digital converter during a zero-flow condition; means for adjusting the output of the analog to digital converter by the determined offset value; a buffer for storing a selected number of digital values corresponding to samples of the transducer output taken over the selected time interval; means for adding a newly acquired digital value to the buffer and subtracting the oldest acquired digital value from the buffer; and first means for processing the buffer contents to identify a zero-flow condition through the flow path in response to the digital values stored in the buffer not varying more than a selected number of digital counts. - View Dependent Claims (9, 10, 11, 12, 13)
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Specification