Patent ID: 7347098

Claim:
Apparatus for providing an output proportional to pressure (P) divided by temperature (T) ( P T ) comprising: an operational amplifier having an inverting input terminal (−), a non-inverting input terminal (+) and an output terminal, a pressure transducer having a bridge array including at least one piezoresistive element and having a voltage biasing terminal coupled to one arm of the bridge, with the other arm of the bridge coupled to a point of reference potential, with the output of the bridge taken between the center terminal of each bridge arm, means for connecting said output terminal of said operational amplifier to said voltage biasing terminal of said bridge, a first voltage divider including a resistor element which varies resistance according to temperature (RTD) in series with a first fixed resistor (R 3 ) with one terminal of said fixed resistor adapted to be connected to a source of voltage (V in ) with said other terminal of said first resistor connected to one terminal of said resistor element to form a common junction, with the other terminal of said resistor element connected to a point of reference potential with said common junction connected to said inverting input terminal off said operational amplifier, a second voltage divider having a second (R 1 ) and third (R 2 ) resistor in series between a first terminal adapted to be connected to said source of voltage (V in ) and a second terminal adapted to be connected to a point of reference potential, with the common junction between said second and third resistors connected to said non-inverting terminal of said operational amplifier, a feedback resistor (R 4 ) connected between said output terminal of said operational amplifier and said inverting terminal whereby the gain of said amplifier changes with temperature, and where said second and third resistors change the offset of the output voltage of said amplifier to cause said amplifier to provide an output voltage at said output terminal directly proportional to 1/and therefore to cause said pressure transducer to provide an output proportional to P/T.