Abstract: There is provided a differential amplifier having a plurality of inputs connected through input resistors to a summing junction at the inverting input of a differential amplifier which also has a negative feedback path having a feedback resistor. One of the input resistors is connected to the output signal of the primary element or transducer. A second of the input resistors is connected to a zero compensating signal which varies with changes in the temperature of the transducer from a certain value at a reference temperature. A third input resistor is connected to a fixed signal of a value which is adjusted to correspond to the certain value of the compensating signal at the reference temperature but of opposite polarity so as to tend to cancel the compensating signal when the transducer is at the reference temperature. The combination of the three inputs then produces an output from the differential amplifier corrected for changes in the zero of the measurement due to temperature changes.

Abstract: The displacement of the diaphragm in a differential pressure sensor of the differential capacitor type produces an output signal substantially linearly related to the displacement. The capacitors are charged in parallel from a constant current source for a fixed period of time and discharged through separate discharge circuits for another fixed period of time. An integrating differential amplifier connected to the two capacitors as they discharge produces an output signal related to the area between the two discharge curves which is substantially linearly related to the extent of displacement of the diaphragm of the differential pressure sensor. The output from the amplifier is used to control the current output from the device.