Abstract: A pressure measuring system which includes a pressure sensitive capacitor and a reference capacitor, a source of external excitation connected to the sensing capacitor, the reference capacitor being connected to a feedback signal generating circuit and the output from said capacitors being summed by a summing junction to produce an error signal. A phase sensitive demodulator is connected to receive the error signal and input same to a feedback signal generating circuit to generate the feedback signal for the reference capacitor. The feedback signal generating circuit includes a computing circuit for generating a digital signal corresponding to the magnitude of said feedback signal required to null said sensing capacitor signal to thereby provide a measurement of pressure.

Abstract: In a pressure measuring system which includes a pressure transducer for generating an analogue signal as a function of pressure, circuitry for generating a non-linear error signal as a function of the difference between the input signal and a feedback signal, a feedback circuit which generates the feedback signal as a function of said error signal to null the error signal and generates a digital output signal as a function of the pressure, a pressure surge detecting circuit having an amplitude detector connected to said pressure measuring system to receive the error signal and generating an output signal when the error signal is equal to and greater than a predetermined magnitude; a timer circuit connected to receive said output signal and generate an alarm signal when the output signal continues for a predetermined period of time, a digital computing circuit connected to receive the digital output signal for computing the rate of change of pressure and the change in pressure, a memory circuit storing predete

Abstract: A pressure ratio measuring system is disclosed. The system includes two quartz capacitive pressure transducers (16, 22). Each capsule contains a pressure sensitive capacitor (Csa, Csf) which is fed by an alternating excitation signal. Capacitance (Csa) is fed by excitation signal (Vr) and Capacitance (Csf) is fed out of phase by feedback excitation signal (-Vr f(N)). The outputs of the capacitance are combined in a summing junction (36) whose output is an error signal (Ie) proportional to the pressure ratio. A feedback loop (26) is closed through a register (30) and a multiplying digital to analog converter (32) to generate the feedback signal (-Vr f(N)). The feedback loop (26) integrates the error signal (Ie) by incremental changing the feedback signal (-Vr f(N)) with digital number (N) in a direction to null the loop. When the loop is nulled the digital number (N) is a representation of the ratio (Pa/Pb) of the pressure (Pa) sensed by capacitance (Csf).

Abstract: A pressure parameter measurement system includes a parameter measurement loop (24, 16, 26, 28, 30, 32, 34) generating a digital signal (N1) indicative of a parameter (Pa-Pb) being measured, a common mode measurement loop (24, 22, 36, 38, 40, 42, Cfa) generating a digital signal (N2) indicative of an element (Pa) of the parameter (Pa-Pb), and a calibration circuit (46) which outputs the parameter (Pa-Pb) as a function of the digital signals (N1, N2) and a temperature signal T.

Abstract: A differential pressure measuring system is disclosed. The system includes two quartz capacitive pressure transducers (14, 16). Each capsule contains a pressure sensitive capacitor (Csa, Csb) and a relatively pressure invariable reference capacitor (Cra, Crb). The pressure sensitive capacitors (Csa, Csb) are excited by out-of-phase signals, (Vr, -Vr) which further excite the reference capacitors (Cra, Crb), out of phase, respectively. The outputs of all capacitors are combined in a summing junction (22) whose output controls the count of a digital integrator (34). A closed loop is formed by converting the output of the integrator (34) to a negative feedback signal (lf) which is applied to the summing junction (22) through a feedback capacitor (Cf). The integrator (34) incrementally changes the feedback signal (lf) in a direction to balance the loop. At this point the output of the integrator (34) is representative of the measured differential pressure.

Abstract: The invention provides a pressure measurement system with a substantially constant settlement time. The invention includes a closed loop pressure measurement system having an input impedance configuration and a feedback impedance configuration where a signal from the feedback impedance configuration is used to null or balance a signal from the input impedance configuration. The error between the signals is integrated in a digital integrator to generate a measurement of the sensed parameter. The invention further comprises a means for varying the feedback loop gain of the system as a function of pressure in a manner to compensate for the gain change produced in the system in response to a pressure change.

Abstract: A pressure ratio measuring system is disclosed. The system includes two quartz capacitive pressure transducers (16, 22). Each capsule contains a pressure sensitive capacitor (Csa, Csf) which is fed by an alternating excitation signal. Capacitance (Csa) is fed by excitation signal (Vr) and Capacitance (Csf) is fed out of phase by feedback excitation signal (-Vr f(N)). The outputs of the capacitance are combined in a summing junction (36) whose output is an error signal (Ie) proportional to the pressure ratio. A feedback loop (26) is closed through a register (30) and a multiplying digital to analog converter (32) to generate the feedback signal (-Vr f(N)). The feedback loop (26) integrates the error signal (Ie) by incremental changing the feedback signal (-Vr f(N)) with digital number (N) in a direction to null the loop. When the loop is nulled the digital number (N) is a representation of the ratio (Pa/Pb) of the pressure (Pa) sensed by capacitance (Csf).

Abstract: A pressure transducer (26) is disclosed. A multiplicity of signal plates (Cs, Cr, Csf, Crf) are disposed on a first quartz disc (88). Opposing the signal plates (Cs, Cr, Csf, Crf) across a gap formed by an annular frit (92) is a common plate (94) disposed on a second quartz disc (86). The signal plates (Cs, Cr, Csf, Crf) and common plate (94) form capacitors which are operable to modulate alternating excitation signals applied to the signal plates. The capacitances vary the modulation during deflections of the discs (86, 88) as a result of pressure changes, and the common plate (94) algebraically sums the modulated excitation signals into a single output from the transducer (26).

Abstract: A quartz capacitive pressure transducer including a sensing plate and a reference plate disposed on one quartz substrate which are opposed across a gap by a common plate on another quartz substrate to form capacitances. The substrates are maintained in their opposing relationship by an annular frit which seals a chamber between the substrates to a reference pressure. The reference plate is disposed in the area occupied by the frit annulus to provide a reference capacitance that has a zero pressure gradient.