System and method for obtaining digital outputs from multiple transducers

A transmitter system for responding to analog values from a number of sensing elements in a transducer and providing digitized readings as to the different elements, comprising:

• a number of passive circuit means including the individual sensing elements for providing variable input signals determined by the analog values of the sensing elements;
• analog multiplexer means for selecting individual ones of the passive circuit means;
• amplifier means coupled to the analog multiplexer means and including feedback means coupled to the passive circuit means for defining a variable frequency oscillator having a given nominal frequency therewith;
• digital generator means coupled to the amplifier means and responsive to the variable frequency signal, the digital generator means comprising first counter means responsive to a predetermined number of cycles of the variable frequency signal, clock source means providing a fixed frequency signal at a substantially higher frequency than the nominal frequency of the variable frequency oscillator, and second counter means coupled to count cycles from the clock source means during the interval of the predetermined number of cycles counted by the first counter means;
• and
• means coupled to the analog multiplexer means and the digital generator means for deriving digitized values from the different analog values represented by the different sensing elements.

The method of determining the value of at least one pressure reading taken by a capacitive pressure transducer, comprising:

• sensing the values of pressures at different regions within the transducer by sensing capacitance variations;
• sensing the temperature within the transducer by temperature sensitive resistance;
• successively generating a variable frequency signal whose frequency is centered at a predetermined value for each of the sensed values, the frequency being relatively low in value;
• counting a predetermined number of cycles of the variable frequency signal to define an interval that varies in duration in accordance with the value being sensed;
• deriving a second count at a much higher fixed frequency than the number of cycles in the oscillator during the predetermined interval;
• sequentially repeating the steps for each of the different values being sensed;
• and
• processing the derived counts to calculate a precise corrected reading for the parameter being sensed by the transducer.

A system for precisely determining the pressure being sensed by a capacitive pressure transducer, comprising:

• a set of at least three capacitive sensing electrode pairs disposed within the transducer and each separately sensing a different static pressure value to provide a capacitance corresponding thereto;
• at least one temperature sensing resistor disposed within the transducer for sensing the temperature of at least a portion thereof;
• oscillator means associated with the different ones of the sensing means and responsive to an enable signal and the value sensed by the electrode pairs or resistor individually for producing a cyclic signal at a frequency proportional to the associated pressure or temperature level, the capacitive or resistive means being in circuit with the oscillator means and a part thereof;
• processor means for providing counter enable signals and separately and successively enabling the oscillator means;
• means coupled to the oscillator means for combining signals therefrom into a given circuit path;
• first counter means coupled to said means for combining and responsive to a counter enable signal from the data processor means for counting a predetermined number of cycles produced by the enabled oscillator means;
• second counter means responsive to the counter enable signal and responsive to the interval of actuation of the first counter means for providing a second count indicative of the duration of the first count;
• high frequency clock means coupled to the second counter means;
• and
• wherein the data processor means is coupled to receive the count from the second counter means and includes means for interrelating the counts represented by the different capacitive and temperature resistance values to derive a composite value representative of the pressure being sensed by the transducer.