Two wire current transmitter responsive to a resistive temperature sensor input signal
First Claim
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1. A resistance-to-current converter system comprising:
- a. a sensing resistor responsive to a variable physical condition to be indicated,b. a bridge including said resistor, said bridge having input and output junctions and being balanced only when said resistor has a predetermined value, whereby the bridge voltage developed at said output junctions is a function of the deviation of the resistor from said predetermined value as a result of a change in said physical condition,c. a D-C amplifier whose input circuit is connected to the output junctions of said bridge whereby the impedance in the output circuit of the amplifier varies as a function of said bridge voltage,d. a direct-voltage source providing an operating voltage both for said bridge and said amplifier,e. a load connected in series with said source and having an output current flow therethrough resulting from variations in said resistor and hence indicative of said condition,f. a voltage regulator,g. a pair of wires connecting said series-connected source and load through said regulator across both the output circuit of said amplifier and the input junctions of said bridge, whereby the operating voltage of said amplifier is stabilized despite variations in said output current flow through said load resulting from variations in the value of said resistor,h. a feedback resistor connected in series with said load to produce a feedback voltage, andi. means to feed said feedback voltage into the arm of said bridge containing said sensing resistor in series opposition to the voltage produced by the sensing resistor to rebalance the bridge, whereby the output current is accurately proportional to changes in said resistor.
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Abstract
Circuitry including a resistance sensor is excited by an external power source. A reference voltage is established, the voltage developed across the sensor resistance is compared at an amplifier input with a reference voltage signal and the voltage across a feedback resistor, and the total current drawn through the circuitry adjusts as a function of the sensor resistance to give a balanced amplifier input. Total current may be made a linear function of sensor resistance or a non-linear function by proper selection of certain resistors.
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Citations
11 Claims
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1. A resistance-to-current converter system comprising:
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a. a sensing resistor responsive to a variable physical condition to be indicated, b. a bridge including said resistor, said bridge having input and output junctions and being balanced only when said resistor has a predetermined value, whereby the bridge voltage developed at said output junctions is a function of the deviation of the resistor from said predetermined value as a result of a change in said physical condition, c. a D-C amplifier whose input circuit is connected to the output junctions of said bridge whereby the impedance in the output circuit of the amplifier varies as a function of said bridge voltage, d. a direct-voltage source providing an operating voltage both for said bridge and said amplifier, e. a load connected in series with said source and having an output current flow therethrough resulting from variations in said resistor and hence indicative of said condition, f. a voltage regulator, g. a pair of wires connecting said series-connected source and load through said regulator across both the output circuit of said amplifier and the input junctions of said bridge, whereby the operating voltage of said amplifier is stabilized despite variations in said output current flow through said load resulting from variations in the value of said resistor, h. a feedback resistor connected in series with said load to produce a feedback voltage, and i. means to feed said feedback voltage into the arm of said bridge containing said sensing resistor in series opposition to the voltage produced by the sensing resistor to rebalance the bridge, whereby the output current is accurately proportional to changes in said resistor. - View Dependent Claims (2, 3, 4, 5, 6)
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7. An electrical current transmitting system comprising a pair of current terminals adapted for connection to a load and power source that are in series;
- a resistance network means connected in series with said current terminals to be powered and excited solely therethrough and including a first resistor which varies in resistance value as a function of temperature, for providing a first variable D.C. voltage signal which varies as a function of the temperature to be measured;
a feedback resistance means connected to said resistance network means;
means to be powered solely through said terminals connected to the feedback resistance means and to the current terminals to establish a current flow path between said terminals and to provide a known portion of current flowing between said terminals through said feedback resistance means to provide a second D.C. voltage signal which is a function of the current through said current terminals including an amplifier means having a voltage input portion and an output portion providing an output signal which is a function of the voltage at said voltage input portion, and current control and adjustment means coupled to said output portion to receive the output signal and to adjust the current in said current flow path between said terminals as a function of said output signal; and
means to couple said resistance network means and said feedback resistance means to said voltage input portion to provide a voltage at said input portion of said amplifier means which is a function of said first and second voltage signals. - View Dependent Claims (8, 9, 10, 11)
- a resistance network means connected in series with said current terminals to be powered and excited solely therethrough and including a first resistor which varies in resistance value as a function of temperature, for providing a first variable D.C. voltage signal which varies as a function of the temperature to be measured;
Specification