Resistance-bridge to frequency converter with automatic offset correction
AssigneeGeneral Electric Company
InventorMiran Milkovic
Life of this patent
Estimating the term…
Abstract
A circuit for converting changes in a sensed physical parameter, such as resistance and resistance change as a function of pressure, temperature and the like, into a digital signal of proportional frequency. A sensor bridge, monitoring the parameter to be measured, forms a part of a feedback loop controlling a current into a resistance-capacitance integrator which is part of a controlled oscillator. The oscillator has automatic offset error correction. The frequency of the sensor-controlled is proportional to the unbalance in the sensor bridge. The converter receives power on a two-wire line from a power supply which may be located remotely therefrom, and from which power supply the sensed-parameter-established frequency is extracted for use by processing-control apparatus and the like.
Claims14
A circuit for converting the magnitude of a sensed physical parameter to the periodic frequency of a waveform, comprising:
- a sensor having first through fourth terminals and having an equivalent electrical resistance appearing between each pair of said terminals, which resistance varies proportional to the magnitude of the physical parameter to be sensed;
- means connected to the first and second terminals of said sensor for providing a current flow of an essentially constant magnitude through the resistances of said sensor;
- means connected to the third and fourth terminals of said sensor for generating a first voltage having a magnitude proportional to the magnitude of the physical parameter sensed by said sensor;
- and
- means for converting said first voltage to said waveform having a frequency substantially proportionally to the magnitude of said sensed physical parameter, including first and second reference potential sources, having essentially identical magnitudes and opposite polarities;
- means having first and second inputs respectively receiving said first voltage and a second voltage for integrating, with respective to time, the sum of the first and second voltages to provide an output voltage;
- comparative means receiving said first and second reference potentials and said output voltage of said integrating means for providing first or second signals when the output voltage of said integrating means is equal to said first or second reference potentials, respectively;
- and
- means for connecting said first or second reference potential to a common node, at which said second voltage appears with polarity selected to reverse the integration direction of said integrating means, responsive respectively to the generation of said comparing means first or second signal;
- each of said first and second signals periodically alternating in polarity at a frequency substantially proportional to said first voltage;
- one of said first and second signals being said waveform.
The converter circuit of claim 3, further comprising a bistable storage circuit having first and second inputs respectively receiving said first and second signals from said first and second comparators, and having a first output which is set and reset, and a second output which is reset and set, responsive respectively to the presence of said first and second signals.
Dependencies are inferred from the claim text.