Electricity: measuring and testing – Impedance – admittance or other quantities representative of... – Lumped type parameters
Reexamination Certificate
1998-07-31
2001-04-10
Metjahic, Safet (Department: 2858)
Electricity: measuring and testing
Impedance, admittance or other quantities representative of...
Lumped type parameters
C324S678000
Reexamination Certificate
active
06215319
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to systems for measuring variable physical parameters by creating a variable reference. More specifically, the invention relates to a system for varying the reference above and below the magnitude of the variable physical parameter that is being measured, and determining the magnitude of the parameter by calculating a function of the difference between the reference and the parameter.
BACKGROUND OF THE INVENTION
Prior systems for measuring variable physical parameters typically comprise the following steps: creating a variable reference; comparing the variable reference to the parameter being measured; and varying the magnitude of the reference until it is substantially equal to that of the parameter. Such systems create a digital signal representative of the magnitude of the reference and employ the digital signal in signal processing to create whatever output is desired from the measuring system.
Generally, the step of creating the digital signal requires using a device known as a comparator. A comparator has a bistable output which changes state according to the sign of the difference between two input signals. Unfortunately, the speed with which such a device reacts to a change of the sign of the difference is dependent upon the magnitude of the difference and/or the rate of change of the difference. Further, as a consequence of its bistable operation, comparators exhibit hysteresis. Hysteresis can cause a comparator's measurement to vary according to the direction from which the magnitude of the reference approaches the magnitude of the parameter. These limitations in comparator technology have diminished the accuracy and success of prior measuring systems. Thus, there is a need in the art for a high-accuracy measurement system that compensates for limitations in comparator technology. Further, such a system should operate with low power comparators and be inexpensive as well as simple to operate.
SUMMARY OF THE INVENTION
The present high accuracy measuring system addresses the above described and other shortcomings in the art. According to one aspect of the invention there is provided a measuring system comprising the following elements: a source electrical circuit which presents a variable physical parameter signal; a digital to analog converter having a reference input for accepting a reference signal and a data input for accepting a data signal, which digital to analog converter generates a variable reference signal; an amplifier electrically connected to the digital to analog converter and the source circuit, which amplifier generates a difference signal representative of the difference between the variable reference signal and the variable physical parameter signal; a comparator electrically connected to the amplifier, which comparator generates a bistable signal indicative of the sign of the difference signal; and a logic device electrically connected to the comparator and the digital to analog converter, which logic device has a first input for receiving the bistable signal from the comparator and a first output for sending a data signal to the data input of the digital to analog converter. The logic device varies the data signal transmitted to the digital to analog converter so as to cause the variable reference signal generated by the digital to analog convertor to oscillate between two limiting values. A mathematical function of the two values provides a measurement of the variable physical parameter. In a preferred embodiment the logic device is a microcomputer and the mathematical function is the average of the two limiting values.
According to one embodiment, the system may further comprise an integrator electrically connected to the amplifier. The integrator generates an integrated signal proportional to the time integral of the difference signal. The comparator is electrically connected to the integrator and generates a bistable signal indicative of the sign of the integrated signal. In such a system the logic device varies, at a substantially constant rate and as a function of the bistable signal, the data signal transmitted to the digital to analog converter so as to cause the variable reference signal to oscillate at a fixed rate between the two limiting values.
According to another aspect of the invention, there is disclosed a method for measuring a variable physical parameter. The method comprises the following steps: presenting a variable physical parameter signal; generating a variable reference signal; generating a signal representative of the difference between the variable reference signal and the variable physical parameter signal; generating a bistable signal indicative of the sign of the difference; varying the variable reference signal so that the variable reference signal oscillates between two limiting values, wherein a mathematical function, preferably the average, of the two values is a measurement of the variable physical parameter signal. In an alternative embodiment the physical parameter signal may be a function of the limiting values and prior measured limiting values.
In a preferred embodiment, the method of measuring a variable physical parameter may further comprise the step of taking the time integral of the difference and generating a bistable signal indicative of the sign of the time integral. In such a method, the variable reference signal may be varied at a substantially constant rate and as a function of the bistable signal, so that the variable reference signal oscillates at a fixed rate between the two limiting values.
REFERENCES:
patent: 3746975 (1973-07-01), Maltby
patent: 3993947 (1976-11-01), Maltby et al.
patent: 4434407 (1984-02-01), Healey, III et al.
patent: 4718036 (1988-01-01), Halbert et al.
patent: 4815001 (1989-03-01), Uthe et al.
patent: 5521556 (1996-05-01), O'Shaughnessy et al.
Hafer Kevin G.
Kramer L. Jonathan
Metjahic Safet
Nguyen Vincent Q.
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