Abstract: A polycrystalline pressure sensor is formed by depositing polycrystalline silicon piezoresistors on a polycrystalline sensing diaphragm. The piezoresistors are arranged in a wheatstone bridge configuration. During operation, an alternating differential signal is applied across the input of the wheatstone bridge. A measured voltage difference between the output terminals of the wheatstone bridge is used to detect imbalance in the electrical piezoresistors that corresponds to pressure applied to the sensor. Pressure is thereby measured.

Abstract: An apparatus and method for automatically adjusting the control parameters of a self-tuning controller used to regulate a process having a measured process variable signal. Using the measured process variable signal, an error signal representing a closed-loop response of the process to an upset condition is generated. Local extrema of the error signal is measured and three successive amplitude values are selected to produce measured decay and overshoot characteristics of the error signal. The three successive amplitude values are selected such that the measured decay characteristic is greater than the overshoot characteristic. Based on the measured decay and overshoot characteristics at least one of the control parameters of the controller is automatically adjusted to improve the difference between one of the measured characteristics and a target characteristic.

Abstract: A method and apparatus for increasing the resolution and accuracy of flow measurements made by vortex flowmeters through the use of an adaptive filter. A vortex sensor signal is conditioned by a bandpass filter whose corner frequencies are dynamically altered as a function of the measured frequency of the vortex sensor signal. When the change in frequency is relatively small, the filters' corner frequencies are set to track the frequency signal in accordance with a specified bandwidth thereby improving the signal-to-noise ratio. For large frequency changes, a new frequency signal is searched for thereby avoiding tracking erroneous noise signals. Furthermore, compensation for additional or missed vortex pulses is made thereby generating a more accurate vortex frequency measurement.

Abstract: An analog isolation circuit for providing electrical isolation between interrelated electrical circuitry contained within a vortex flowmeter. The circuit provides a low power and low cost solution to the problem of ground isolation presented in flowmeters utilizing grounded sensors which generate low frequency sinusoidal signals. A pair of clock-controlled analog switches couples the voltage difference between two successive samples of an analog signal across an isolation barrier. The operation of the switches at a low frequency rate and with a short sampling interval while utilizing a low magnetizing current preserves the magnitude of the input waveform while consuming approximately 1 mW of power.

Abstract: A method and apparatus for a robust process control system that utilizes a neural-network multivariable inner-loop PD controller cascaded with decoupled outer-loop controllers with integral action, the combination providing a multivariable nonlinear PID and feedforward controller. The inner-loop neural-network controller is trained to achieve optimal performance behavior when future process behavior repeats the training experience. The outer-loop controllers compensate for process changes, unmeasured disturbances, and modeling errors. In the first and second embodiments, the neural network is used as an inner-loop controller in a process control system having a constraint management scheme which prevents integral windup by controlling the action of the outer-loop controllers when limiting is detected in the associated manipulated-variable control path.

Abstract: A method and apparatus for a robust process control system which utilizes a neural-network based multivariable inner-loop PD controller cascaded with decoupled outer-loop controllers with integral action, the combination providing a multivariable nonlinear PID and feedforward controller. The inner-loop PD controller employs a quasi-Newton iterative feedback loop structure whereby the manipulated variables are computed in an iterative fashion as a function of the difference between the inner loop setpoint and the predicted controlled variable as advanced by the optimum prediction time, in order to incorporate the downstream limiting effects on the non-limited control loops. The outer-loop controllers compensate for unmodeled process changes, unmeasured disturbances, and modeling errors by adjusting the inner-loop target values.

Abstract: Multivariable adaptive feedforward control may be accomplished by detecting the beginning and ending of a process control disturbance response, characterizing the measured inputs and process output during the disturbance by moments, which comprise time-weighted integrals performed on the process result output and inputs when the disturbance is a measured disturbance, and relating the characterized inputs and process result output in known general transfer function model equations to generate transfer function parameters which are used to calculate the coefficients of feedforward additive or multiplicative compensators.