TWO WIRE TELEMETRY SYSTEM

• US 3,680,384 A
• Filed: 08/20/1968
• Issued: 08/01/1972
• Est. Priority Date: 08/20/1968
• Status: Expired due to Term

• Current Assignee: Earl A. Grindheim
• Original Assignee: Earl A. Grindheim
• Inventors: Grindheim, Earl A.
• Primary Examiner(s): Swisher, Clement
• Assistant Examiner(s): Shoon, Frederick
• Application Number:
  US04/753,937
• Time in Patent Office: 1,442 Days
• Field of Search: 324/57B,62B,65B,30 323/4,22T,75H,75N 73/88.5,362R,362AR,359,361 340/186
• US Class Current: 340/870.43
• CPC Class Codes: G01K 1/024 for remote indication
• CPC Class Codes: G08C 19/02 in which the signal transmitted is magnitude of current or voltage G08C19/36, G08C19/38 take precedence

Abstract

Measuring circuitry including a current controller which has an internal amplifier, and which controls current in response to differential input signals, is excited by an external power source. A reference voltage is established, and a separate voltage signal is also developed from a separate voltage source such as a thermocouple. The reference voltage is compared at an amplifier input with the voltage signal. A voltage is developed across a feedback resistor, and the total current through the circuitry adjusts until the feedback signal balances the signal inputs to the current controller. Total current drawn is thus a function of the voltage signals.

Claims

1. Electrical apparatus comprising a first circuit having a current input and a current output, a current controller in said first circuit, a first DC voltage signal input means, a second DC voltage signal input means, amplifier and control means in said current controller connected to both of said signal input means for controlling the total current flow to the current output in response to voltage signals at said voltage signal input means, said controller being connected between said current input and said current output for receiving its power only through said current input, a resistance network connected in circuit with said controller through which at least a certain portion of the current flowing from the current controller flows to provide a feedback signal responsive to said current flowing through the current controller, and means electrically connecting said resistance network to one of the voltage signal input means to couple the feedback signal to said one voltage signal input means, said feedback signal modifying the signal at said one voltage signal input means in response to changes in current flow from the current controller through said resistance network to balance the voltage signals at the voltage signal input means, one of the voltage signal input means including a separate unknown source of voltage.

2. The electrical apparatus of claim 1 wherein said controller means operates at a predetermined minimum current flow, and circuit means connected to said resistance network and energized by a portion of the total current flow from the current input to provide a reference voltage for the other of the signal inputs, and being effective to maintain balance between the signal inputs with the predetermined minimum current flowing until the separate source of voltage exceeds a predetermined minimum level.

3. A two wire current transmitter comprising a current input terminal and a current output terminal for passing a current therebetween whose magnitude is proportional to a measured variable, a resistance network connected in series with said input and output terminals, said network having a first resistor which varies in magnitude as a function of a physical condition to provide a first voltage signal and a second resistor which provides a second voltage signal proportional to total transmitter current passing from said current input terminal, a voltage responsive current controller including amplifier means, current adjustment means controlled by said amplifier means, first and second current energization terminals and signal input terminal means, said current energization terminals being in series with said current input and output terminals and providing the sole energization for the controller, said current energization terminals also being in series with said second resistor, means connected between said resistance network and said signal input means for changing said first voltage signal in accordance with the magnitude of a variable condition, and voltage terminal means connected to said resistance network and said last-mentioned means, said last-mentioned means being connected to said signal input terminal means, so that the current adjustment means of said controller adjusts the transmitter current through said second resistor in response to said first and second voltage signals as modified by said last-mentioned means, said last-mentioned means including a thermocouple and said first resistor being temperature dependent to provide cold junction compensation for said thermocouple.

4. A two wire current transmitter comprising a pair of current terminals for passing a load current therebetween whose magnitude is proportional to a variable condition, a resistance network connected in series with said current terminals, said network including a first resistor through which a first portion of said load current flows to provide a first voltage at one location on said network and said network including a second resistor through which a second portion of said load current flows, said second current portion being a percentage of said load current, to provide a second voltage at a second location on said network which is proportional to said load current, a controller energized solely from said current terminals including voltage responsive means having a pair of voltage terminals and current adjusting means controlled by said voltage responsive means, means including a thermocouple connected between said one location and one of said voltage terminals for introducing a voltage signal changing in accordance with the magnitude of said variable condition, means connecting said current adjusting means in circuit with said second resistor to change the voltage at said one location in a direction so as to return the voltage applied to said voltage terminals to substantially the same value prevailing before a change in the magnitude of said variable condition occurred, whereby the load current comprised of said first and second current portions represents the magnitude of said variable condition.

5. A measuring system comprising a pair of current terminals, a source of direct current and a load connected in series between said current terminals so that all of the load current provided by said source flows through said load and said current terminals, a controller energized solely from said current terminals including a voltage responsive means and a current adjusting means in circuit with said current terminals controlled by said voltage responsive means, means connected to said voltage responsive means for applying a direct current voltage to said voltage responsive means that changes in value due to a change in magnitude of a variable condition so as to provide a current flow through said adjusting means the value of which is determined by the voltage supplied by said applying means, said voltage applying means including a separate unknown source of voltage, resistance means in circuit with said current adjusting means so that the current flowing through said adjusting means determines the current flowing through said resistance means and the voltage thereacross, means connecting said resistance means to said voltage applying means to utilize the voltage across said resistance means as determined by the adjusted current therethrough to return the value of voltage applied to said voltage responsive means To substantially its same value as before a change in voltage occurred due to a change in magnitude of said variable condition, whereby an adjustment in the value of current flowing through said current adjusting means also causes a change in value of load current which is representative of the change in magnitude of said variable condition.

6. The measuring system of claim 5 including voltage reference means connected in circuit with said resistance means for providing a reference voltage with respect to which said direct current voltage varies.

7. Electrical apparatus comprising a first circuit having a current input and a current output, a current controller in said first circuit, a first DC voltage signal input means, a second DC voltage signal input means, amplifier and control means in said current controller connected to both of said signal input means for controlling the total current flow to the current output in response to voltage signals at said voltage signal input means, said controller being connected between said current input and said current output for receiving its power only through said current input, a resistance network connected in circuit with said controller through which at least a certain portion of the current flowing from the current controller flows to provide a feedback signal responsive to said current flowing through the current controller, and means electrically connecting said resistance network to one of the voltage signal input means to couple the feedback signal to said one voltage signal input means, said feedback signal modifying the signal at said one voltage signal input means in response to changes in current flow from the current controller through said resistance network to balance the voltage signals at the voltage signal input means, one of the voltage signal input means comprising a thermocouple.

8. A measuring system comprising a pair of current terminals, a source of direct current and a load connected in series between said current terminals so that all of the load current provided by said source flows through said load and said current terminals, a controller energized solely from said current terminals including a voltage responsive means and a current adjusting means in circuit with said current terminals controlled by said voltage responsive means, means connected to said voltage responsive means for applying a direct current voltage to said voltage responsive means that changes in value due to a change in magnitude of a variable condition so as to provide a current flow through said adjusting means the value of which is determined by the voltage supplied by said applying means, said voltage applying means including a thermocouple, resistance means in circuit with said current adjusting means so that the current flowing through said adjusting means determines the current flowing through said resistance means and the voltage thereacross, means connecting said resistance means to said voltage applying means to utilize the voltage across said resistance means as determined by the adjusted current therethrough to return the value of voltage applied to said voltage responsive means to substantially its same value as before a change in voltage occurred due to a change in magnitude of said variable condition, whereby an adjustment in the value of current flowing through said current adjusting means also causes a change in value of load current which is representative of the change in magnitude of said variable condition.

9. The system of claim 8 including voltage reference means connected in circuit with said resistance means for providing a reference voltage with respect to which said direct current voltage varies.

10. A measuring system comprising a pair of current terminals, a source of direct current and a load connected in series between said current terminals so that all of the load current provided by said source flows through said load and said current terminals, a controller energized solely from saId current terminals including a voltage responsive means and a current adjusting means in circuit with said current terminals controlled by said voltage responsive means, means connected to said voltage responsive means for applying a direct current voltage to said voltage responsive means that changes in value due to a change in magnitude of a variable condition so as to provide a current flow through said adjusting means the value of which is determined by the voltage supplied by said applying means, said voltage applying means including a pair of conductor lines and a separate unknown source of voltage in series with one of said lines, resistance means in circuit with said current adjusting means so that the current flowing through said adjusting means determines the current flowing through said resistance means and the voltage thereacross, means connecting said resistance means to said voltage applying means to utilize the voltage across said resistance means as determined by the adjusted current therethrough to return the value of voltage applied to said voltage responsive means to substantially its same value as before a change in voltage occurred due to a change in magnitude of said variable condition, whereby an adjustment in the value of current flowing through said current adjusting means also causes a change in value of load current which is representative of the change in magnitude of said variable condition.

11. A measuring system comprising a pair of current terminals, a source of direct current and a load connected in series between said current terminals so that all of the load current provided by said source flows through said load and said current terminals, a controller energized solely from said current terminals including a voltage responsive means and a current adjusting means in circuit with said current terminals controlled by said voltage responsive means, means connected to said voltage responsive means for applying a direct current voltage to said voltage responsive means that changes in value due to a change in magnitude of a variable condition so as to provide a current flow through said adjusting means the value of which is determined by the voltage supplied by said applying means, said voltage applying means including a pair of conductor lines and a thermocouple connected in series with one of said lines, resistance means in circuit with said current adjusting means so that the current flowing through said adjusting means determines the current flowing through said resistance means and the voltage thereacross, means connecting said resistance means to said voltage applying means to utilize the voltage across said resistance means as determined by the adjusted current therethrough to return the value of voltage applied to said voltage responsive means to substantially its same value as before a change in voltage occurred due to a change in magnitude of said variable condition, whereby an adjustment in the value of current flowing through said current adjusting means also causes a change in value of load current which is representative of the change in magnitude of said variable condition.