Differential pressure measuring system

A differential pressure measuring system comprising:

• means for generating first and second alternating reference signals having a predetermined phase relationship therebetween;
• a first pressure sensitive impedance, responsive to a first pressure, driven by said first reference signal for generating a signal proportional to the change in the first pressure;
• a second pressure sensitive impedance, responsive to a second pressure, driven by said second reference signal for generating a signal proportional to the change in the second pressure;
• means, electrically connected to said first and second impedances, for generating an analog error signal which is proportional to the difference between said first and second pressures;
• means for converting said analog error signal into a digital error signal;
• means for integrating said digital error signal and generating a digital output number N therefrom;
• means for converting said digital output number into an alternating feedback signal of the same phase as one of said reference signals;
• wherein said feedback signal is fed back to said analog error signal generating means through a feedback impedance to null said analog error signal;
• and
• said digital output number N being representative of the difference in said first and second pressures when the digital error is nulled.