TELEMETRY METHOD AND APPARATUS

• US 3,825,733 A
• Filed: 08/11/1971
• Issued: 07/23/1974
• Est. Priority Date: 08/11/1971
• Status: Expired due to Term

• Current Assignee: Daniel L. Craig, Dowell White
• Original Assignee: Daniel L. Craig, Dowell White
• Inventors: White, Dowell, Craig, Daniel L.
• Primary Examiner(s): Ruggiero, Joseph F.
• Application Number:
  US05/170,736
• Time in Patent Office: 1,077 Days
• Field of Search: 235/151.31,151.3 340/150,151,152,177-179,201,210 179/2 329/201 318/641 324/57,62,105,73AT
• US Class Current: 702/65
• CPC Class Codes: G01K 7/021 Particular circuit arrangements G01K7/026, G01K7/12, G01K7/14 take precedence

Abstract

A method and apparatus for telemetry, wherein first and second electrical signals are generated and applied across a remotely located electrical quantity, such as voltage or resistance, desired to be measured. The interaction of such first and second electrical signals with the electrical quantity to be measured produces first and second resultant electrical signals which are used by a computer or analog portion of the telemeter to determine the value of the electrical quantity in question.

Claims

1. A method of telemetering to a first location the value of an electrical quantity located at a second location, the first and second locations being connected by two conductors, including the steps of:

generating alternately at the first location first and second electrical signals of opposite polarity;

regulating each of the first and second electrical signals so that one of the electrical components of current and voltage of the first and second electrical signals is maintained constant;

transmitting the regulated first and second electrical signals individually through the conductors to the second location and applying at least one of the regulated first and second electrical signals to the electrical quantity, whereby the resistance of the conductors is substantially compensated for;

detecting the other of the electrical components of current and voltage of first and second resultant electrical signals flowing through the conductors as a result of the interaction of the regulated first and second electrical signals with the resistance of the conductors and at least one of the first and second regulated electrical signals with the electrical quantity; and

determining from the detected electrical component of the first and second resultant electrical signals the value of the electrical quantity, whereby the resistance of the conductors produces no substantial error in the determination.

2. A method of telemetering to a first location the value of an electrical quantity located at a second location, wherein the electrical quantity is the voltage produced by the measuring junction of the thermocouple, wherein the thermocouple has associated therewith a means for compensating for the voltage generated by its reference junction and a means for compensating for the resistance of the conductors, according to claim 1, in which:

the detecting step includes detecting both the voltage and current components of the first and second resultant electrical signals; and

, the determining step includes solving Equations (1), (3), and (4).

3. A method of telemetering to a first location the voltage produced by the measuring junction of a thermocouple located at a second location, wherein the first and second locations are connected by two electrical conductors, wherein the thermocouple has connected in series therewith a reference junction compensation resistor having an ohmage which varies linearly and proportionally to its ambient temperature for a selected range of ambient temperatures, which ohmage is sufficiently large throughout the selected range of temperatures with respect to the resistance of the conductors so that the effects of the resistance of the conductors are negligible, and wherein the reference junction of the thermocouple and the reference junction compensation resistor are maintained in an isothermal enclosure, including the stepS of:

generating alternately at the first location first and second electrical signals, the current components of each of the first and second electrical signals having a selected wave form and magnitude;

transmitting the first and second electrical signals through the conductors to the second location and applying the first and second electrical signals to the thermocouple and the reference junction compensation resistor;

detecting the voltage components of first and second resultant electrical signals flowing through the conductors as a result of the interaction of the first and second electrical signals with the thermocouple, the reference junction compensation resistor, and the resistance of the conductors; and

determining from the voltage components of the first and second resultant electrical signals the voltage produced by the measuring junction of the thermocouple.

4. A method of telemetering according to claim 3 wherein the step of determining from the voltage components of the first and second resultant electrical signals the voltage produced by the measuring junction of the thermocouple includes solving Equations (1), (5) and (6).

5. A method of telemetering according to claim 3 wherein the generating step includes regulating the first and second electrical signals so that the current component of each of the signals is substantially constant and identical in absolute magnitude and is of opposite polarity from the other of the current components.

6. A method of telemetering according to claim 3 wherein the step of determining from the voltage components of the first and second resultant electrical signals the voltage produced by the measuring junction of the thermocouple includes the steps of:

subtracting the absolute value of the voltage component of one of the first and second resultant electrical signals from the absolute value of the voltage component of the other of the first and second resultant electrical signals to obtain a remainder;

dividing the remainder by two to obtain a first quotient;

adding the absolute value of the voltage components of the first and second resultant electrical signals to obtain a sum;

dividing the sum by two to obtain a second quotient;

multiplying the second quotient times a first constant to obtain a product, the first constant being based on the temperature characteristics of the reference junction compensation resistor and being of a value that, when multiplied by the ohmage of the reference junction compensation resistor at any selected temperature within the selected range of temperatures, it yields a voltage equal to the voltage produced by the reference junction of the thermocouple at such temperature; and

adding the absolute value of the first quotient and the absolute value of the product.

7. A method of telemetering according to claim 6 wherein the step of dividing the remainder by two to obtain a first quotient includes also dividing the remainder by a second constant to obtain the first quotient, the second constant being based on the characteristics of the various components comprising the telemetry system and being of a value that, when divided into the remainder, accounts for any efficiency losses existing in the telemetry system.

8. A method of telemetering to a first location the voltage produced by the measuring junction of a thermocouple located at a second location, wherein the first location is connected by two electrical conductors to the second location, wherein the thermocouple has connected in series therewith a reference junction compensation resistor having an ohmage which varies linearly and proportionally to its ambient temperature for a selected range of temperatures, which ohmage is such throughout the range of temperatures that when one of the first and second electrical signals is applied to the reference junction compensation resistor there is produced a voltage drop thereacross with twice the magnitudE of the voltage generated by the reference junction of the thermocouple, wherein there is connected in parallel with the reference junction compensation resistor a variable nulling resistor adjusted to have an ohmage equal to the ohmage of the reference junction compensation resistor at a selected ambient temperature, and wherein at least the reference junction of the thermocouple and the reference junction compensation resistor are maintained in an isothermal enclosure, including the steps of:

generating alternately at the first location first and second electrical signals, the current component of each of the signals having a selected wave form and magnitude;

transmitting the first and second electrical signals through the conductors to the second location and applying one of the first and second electrical signals to the reference junction compensation resistors and the thermocouple and applying the other of the first and second electrical signals to the nulling resistor and the thermocouple;

detecting the voltage components of first and second resultant electrical signals flowing through the conductors as a result of the interaction of the first and second electrical signals with the reference junction compensation resistor, the nulling resistor, the thermocouple, and the resistance of the conductors; and

determining from the voltage components of the first and second resultant electrical signals the voltage produced by the measuring junction of the thermocouple.

9. A method of telemetering according to claim 8 wherein the step of determining from the voltage components of the first and second resultant electrical signals the voltage produced by the measuring junction of the thermocouple includes solving Equation (7).

10. A method of telemetering according to claim 8 wherein the generating step includes regulating the first and second electrical signals so that the current component of each of the signals is substantially constant and identical in absolute magnitude and is of opposite polarity from the other of the current components.

11. A method of telemetering according to claim 8 wherein the step of determining from the voltage components of the first and second resultant electrical signals and the voltage produced by the measuring junction of the thermocouple includes the steps of:

subtracting the absolute value of the voltage component of one of the first and second resultant electrical signals from the absolute value of the voltage component of the other of the first and second resultant electrical signals to obtain a remainder; and

dividing the remainder by two.

12. A method of telemetering to a first location the value of an electrical quantity located at a second location, wherein the electrical quantity is the DC voltage produced by a voltage source, and wherein the voltage source is connected by two electrical conductors to the first location, according to claim 1, in which:

the regulating step includes regulating each of the first and second electrical signals so that the current component of each of the signals is constant and identical in absolute magnitude;

the step of detecting includes detecting the voltage components of the first and second resultant electrical signals; and

the determining steps includes solving Equation (9).

13. A method of telemetering according to claim 12, wherein the step of determining from the voltage components of the first and second resultant electrical signals the DC voltage produced by the voltage source, includes the steps of:

subtracting the absolute value of the voltage component of one of the first and second resultant electrical signals from the absolute value of the voltage component of the other of the first and second resultant electrical signals to obtain a remainder; and

dividing the remainder by two.

14. A method of telemetering to a first location the ohmage of a variable resistance source located at a second location, wherein the first and second locations are connected by two electrical conductors, wherein there is connected in parallel with the resistance source a variable nulling resistor adjusted to have an ohmage equal to the ohmage of the resistance source at a selected condition or state of the resistance source, including the steps of:

generating alternately at the first location first and second electrical signals, the current component of each of the signals having a selected wave form and magnitude;

transmitting the first and second electrical signals through the conductors to the second location and applying one of the first and second electrical signals to the resistance source and the other of the first and second electrical signals to the nulling resistor;

detecting the voltage components of first and second resultant electrical signals flowing through the conductors as a result of the interaction of the first and second electrical signals with the resistance source, the nulling resistor, and the resistance of the conductors; and

determining from the voltage components of the first and second resultant electrical signals the ohmage of the variable resistance source.

15. A method of telemetering according to claim 14 wherein the step of determining from the voltage components of the first and second resultant electrical signals the ohmage of the variable resistance source includes solving Equation (10).

16. A method of telemetering according to claim 14 wherein the generating step includes regulating the first and second electrical signals so that the current component of each of the signals is substantially constant and identical in absolute magnitude and is of opposite polarity from the other of the current components.

17. A method of telemetering according to claim 14 wherein the step of determining from the voltage components of the first and second resultant electrical signals the ohmage of the resistance source includes the steps of:

subtracting the absolute value of the voltage components of one of the first and second resultant electrical signals from the absolute value of the voltage component of the other of the first and second resultant electrical signals to obtain a remainder; and

dividing the remainder by the absolute value of the current component of the first and second electrical signals.

18. A method of telemetering to a first location the composite value of a plurality of electrical quantities of the same type located at a plurality of second locations and connected in a selected network arrangement, the entire network of electrical quantities being connected by two electrical conductors to the first location, according to claim 1, wherein:

the steps of generating, transmitting and applying, detecting, and determining are performed with respect to the network of electrical quantities.

19. A telemeter for telemetering to a first location the value of an electrical quantity located at a second location, comprising:

means at the first location for alternately generating first and second electrical signals of opposite polarity;

means at the first location for regulating one of the components of voltage and current of the first and second electrical signals;

two conductors connecting between the first and second location through which the regulated first and second electrical signals are applied individually from the first location to the second location;

means at the second location for allowing at least one of the regulated first and second electrical signals to be applied to the electrical quantity;

means for detecting the other of the components of voltage and current of first and second resultant electrical signals flowing through the conductors as a result of the interaction of the resistance of the conductors with the regulated first and second electrical signals and the electrical quantity with at least one of the regulated first and second electrical signals; and

means for determining From the detected component of the first and second resultant electrical signals the value of the electrical quantity.

20. A telemeter for telemetering to a first location the voltage generated by the measuring junction of a thermocouple located at a second location, comprising:

means at the first location for alternately generating first and second electrical signals;

means connected in series with the thermocouple at the second location for compensating for the voltage generated by the reference junction of the thermocouple, the reference junction compensation means having a variable ohmage which is linear and proportional to its ambient temperature for a selected range of ambient temperatures, the variable ohmage of the reference junction compensation means being sufficiently large throughout the selected range of temperatures with respect to the resistance of the conductor so that the effects of the resistance of the conductors are negligible;

two conductors connecting between the first and second location through which the first and second electrical signals are applied across both the thermocouple and the reference junction compensation means;

an isothermal enclosure in which the reference junction compensation means and the reference junction of the thermocouple are maintained;

means for detecting the voltage and current components of first and second resultant electrical signals flowing through the conductors as a result of the interaction of the first and second electrical signals with the thermocouple, the reference junction compensation means, and the resistance of the conductors; and

means for determining from the voltage and current components of the first and second resultant electrical signals the value of the voltage of the measuring junction of the thermocouple.

21. A telemeter according to claim 20 wherein the means for determining from the voltage and current components of the first and second resultant electrical signals the value of the voltage of a measuring junction of the thermocouple includes means for solving Equations (1), (3) and (4).

22. A telemeter according to claim 20, including:

means for regulating the first and second electrical signals so that the current component of each of the signals has a selected wave form and magnitude;

the detecting means comprises means for detecting the voltage components of the first and second resultant electrical signals; and

the determining means comprises means for solving Equations (1), (5) and (6).

23. A telemeter according to claim 22 wherein the regulating means regulates the first and second electrical signals so that the current components of each of the signals is substantially constant and identical in absolute magnitude and is of opposite polarity from the other of the current components.

24. A telemeter according to claim 22, wherein the means for solving Equations (1), (5) and (6) is a properly programmed computer.

25. A telemeter according to claim 22, wherein the means for solving Equations (1), (5) and (6) comprises:

means for subtracting the absolute value of the voltage component of one of the first and second resultant electrical signals from the absolute value of the voltage component of the other of the first and second resultant electrical signals to obtain a remainder;

means for dividing the remainder by two to obtain a first quotient;

means for adding the absolute value to the voltage component of the first and second resultant electrical signals to obtain a sum;

means for dividing the sum by two to obtain a second quotient;

means for multiplying the second quotient by a constant to obtain a product, the constant being based on the known temperature characteristics of the reference junction compensation means and being of a value that when multiplied by the ohmage of the reference junction compensation means, it yields a voltage equal to the voltage generated by the reference junction; and

means for adding the absolute value of the first quotient and the absolute value of the product.

26. A telemeter for telemetering to a first location the voltage generated by the measuring junction of a thermocouple located at a second location, comprising:

means at the first location for alternately generating first and second electrical signals;

means for regulating the first and second electrical signals so that the current component of each of the first and second electrical signals has a selected wave form and magnitude;

two conductors connecting between the first and second locations through which the first and second electrical signals are transmitted;

a reference junction compensation resistor connected in series with the thermocouple at the second location, the reference junction compensation resistor having variable ohmage which is linear and proportional to its ambient temperature and possessing temperature/ohmage characteristics such that when a selected one of the first and second electrical signals is applied therethrough there is produced a voltage drop thereacross with twice the magnitude of the voltage generated by the reference junction of the thermocouple;

means connected in parallel with the reference junction compensation resistor at the second location for nulling the reference junction compensation resistor;

means associated with the reference junction compensation resistor at the second location for allowing only one of the first and second electrical signals to flow through the reference junction compensation resistor and means associated with the nulling resistor at the second location for allowing only the other of the first and second electrical signals to flow through the nulling resistor, such flow-allowing means being arranged so that both the first and second electrical signals flow through the thermocouple;

an isothermal enclosure in which at least the reference junction compensation resistor and the reference junction of the thermocouple are maintained;

means for detecting the voltage components of first and second resultant electrical signals flowing through the conductors as a result of the interaction of the first and second electrical signals with the thermocouple, the reference junction compensation resistor, the nulling resistor, and the resistance of the conductors; and

means for determining from the voltage components of the first and second resultant electrical signals the voltage generated by the measuring junction of the thermocouple.

27. A telemeter according to claim 26 wherein the means for determining from the voltage components of the first and second resultant electrical signals the voltage generated by the measuring junction of the thermocouple includes means for solving Equation (7).

28. A telemeter according to claim 27 wherein the means for solving Equation (7) is a properly programmed computer.

29. A telemeter according to claim 26 wherein the regulating means regulates the first and second electrical signals so that the current components of each of the signals is substantially constant and identical in absolute magnitude and is of opposite polarity from the other of the current components.

30. A telemeter according to claim 29 wherein:

the generating means comprises means for generating an alternating current signal wherein each half cycle theref is of opposite polarity and is of substantially square-wave form, the positive half cycles being one of the first and second electrical signals and the negative half cycles being the other of the first and second electrical signals; and

the regulating means comprises means for regulating the peak current of each of the half cycles of the alternating current signal to substantially the same absolute magnitude.

31. A telemeter according to claim 26 wherein:

the nulling means comprises a variable resistor; and

the flow-allowing means comprises at least one diode polarized in a preselected manner and connected in series with each of the reference junction compensation means of the nulling resistor.

32. A telemeter according to claim 26 wherein the means for determining from the voltage components of the first and second resultant electrical signals the voltage generated by the measuring junction of the thermocouple comprises:

means for subtracting the absolute value of the voltage component of one of the first and second resultant electrical signals from the absolute value of the voltage component of the other of the first and second resultant electrical signals to obtain a remainder; and

means for dividing the remainder by two.

33. A telemeter for telemetering to a first location the value of an electrical quantity located at a second location, wherein the electrical quantity is the DC voltage produced by a voltage source, according to claim 20, including:

the regulating means comprises means for regulating the current component of each of the first and second electrical signals so that it has a selected wave form and magnitude;

the detecting means comprises means for detecting the voltage components of the first and second resultant electrical signals; and

the determining means comprises means for solving Equation (9).

34. A telemeter according to claim 33 wherein the regulating means regulates the first and second electrical signals so that the current component of each of the signals is substantially constant and identical in absolute magnitude and is of opposite polarity from the other of the current components.

35. A telemeter according to claim 33 wherein the means for solving Equation (9) of a properly programmed computer.

36. A telemeter according to claim 33;

wherein the means for solving Equation (9) comprises;

means for subtracting the absolute value of the voltage component of one of the first and second resultant electrical signals from the absolute value of the voltage component of the other of the first and second resultant electrical signals to obtain a remainder; and

means for dividing the remainder by two.

37. A telemeter for telemetering to a first location the ohmage of a resistance source located at a second location, comprising:

means at the first location for alternately generating first and second electrical signals;

means for regulating the first and second electrical signals so that the current component of each of the first and second electrical signals has a selected wave form and magnitude;

two conductors connecting between the first location and the second location through which the first and second electrical signals are transmitted;

a nulling resistor connected in series with the resistance source and adjusted to have an ohmage equal to the ohmage of the resistance source at a selected state;

means associated with the resistance source allowing only one of the first and second electrical signals to flow through the resistance source and means associated with the nulling resistor allowing only the other of the first and second electrical signals to flow through the nulling resistor;

means for detecting the voltage components of first and second electrical signals flowing through the conductors as a result of the interaction of the first and second electrical signals with the resistance source, the nulling resistor, and the resistance of the conductors; and

means for determining from the first and second resultant electrical signals the value of the resistance source.

38. A telemeter according to claim 37 wherein the means for determining from the first and second resultant electrical signal the value of the resistance source includes means for solving Equation (10).

39. A telemeter according to claim 38 wherein the means for solving equation (10) is a properly programmed computer.

40. A telemeter according to claim 37 wherein the regulating means regulates the first and second electrical signal so that the current component of each of the signals is substantially constant and identical in absolute magnitude and is of opposite polarity from the other of the current components.

41. A telemeter according to claim 38 wherein the means for determining from the first and second resultant electrical signals the value of the resistance source comprises:

means for subtracting the absolute value of the voltage component of one of the first and second resultant electrical signals from the absolute value of the voltage component of the other of the first and second resultant electrical signals to obtain a remainder; and

means for dividing the remainder by the absolute value of the current component of the first and second resultant electrical signals.

42. A telemeter according to claim 20 wherein the electrical quantity is a plurality of electrical quantities of the same type arranged in a selected network.

43. An apparatus to be coupled through conductors to a remote device for alternately generating first and second electrical signals and for detecting the resultant electrical signals flowing through the conductors as a result of the first and second signals interacting with the apparatus, the apparatus comprising:

a thermocouple having a measuring junction and a reference junction;

means for compensating for the voltage generated by the reference junction of the thermocouple connected in series with the thermocouple, the reference junction compensation means having a variable ohmage which is linear and proportional to its ambient temperature for a preselected range of ambient temperatures, the variable ohmage of the reference junction compensation means being sufficiently large throughout the preselected range of temperatures with respect to the resistance of the conductors so that the effects of the resistance of the conductors are negligible; and

an isothermal enclosure in which at least the reference junction compensation resistor and the reference junction of the thermocouple are maintained.

44. A thermocouple module for connection through electrical conductors with a remotely located generating and detection device which generates alternately first and second electrical signals and applies such signals through the conductors to the thermocouple module and detects the first and second resultant electrical signals flowing through the conductors as a result of the interaction of the first and second electrical signals with the thermocouple module, the thermocouple comprising:

a thermocouple having a measuring junction and a reference junction;

a reference junction compensation resistor connected in series with the thermocouple, the reference junction compensation resistor having a variable ohmage which is linear and proportional to its ambient temperature and possessing temperature/ohmage characteristics such that when the one of the first and second electrical signals is applied therethrough there is produced a voltage drop thereacross with twice the magnitude of the voltage generated by the reference junction of the thermocouple;

means for nulling the reference junction compensation resistor connected in parallel with the reference junction compensation resistor;

means associated with the reference junction compensation resistor for allowing only one of the first and second electrical signals applied through the conductors to the thermocouple module to flow through the reference junction compensation resistor and means associated with the nulling means for allowing only the other of the first and second electrical signals to flow through the nulling means, the flow-allowing means being arranged such that both the first and second electrical signals flow through the thermocouple; and

an isothermal enclosure in which at least the reference junction compensation resistor and the reference junction of the thermocouple are maintAined.

45. A thermocouple module according to claim 44 wherein the nulling means comprises a variable resistor and wherein each of the flow-allowing means comprises at least one diode polarized in a preselected manner and connected in series with the reference junction compensation means and the nulling resistor, respectively.

46. A resistance module for connection through electrical conductors with a remotely located generating and detection device which generates alternately first and second electrical signals and applies such signals through the conductors to the resistance module and detects the first and second resultant electrical signals flowing through the conductors as a result of the interaction of the first and second electrical signals with the resistance module, the resistance module comprising:

a first resistor;

a nulling resistor connected in parallel with the first resistor and adjusted to have a known ohmage equal to the known ohmage of the first resistor at a preselected state; and

means associated with the first resistor allowing only one of the first and second electrical signals applied through the conductors to the resistance module to flow through the first resistor and means associated with the nulling resistor allowing only the other of the first and second electrical signals to flow through the nulling resistor.

47. A generating and determining apparatus for connection through electrical conductors with a remotely located thermocouple module including a thermocouple having a measuring junction and a reference junction and including a reference junction compensation means, the generating and detecting means comprising:

means for generating alternately first and second electrical signals and for applying the signals through the conductors;

means for detecting first and second resultant electrical signals flowing through the conductors as a result of the interaction of the first and second electrical signals with the remotely located thermocouple module; and

means for determining from the first and second resultant electrical signals the value of the measuring junction of the thermocouple contained in the thermocouple module.

48. A generating and determining apparatus for connection through electrical conductors with a remotely located resistance module including a first resistor, a nulling resistor connected in parallel with the first resistor, and means associated with the first resistor and the nulling resistor allowing current to flow in only one direction through each of them, the generating and determining apparatus comprising:

means for generating alternately first and second electrical signals and for applying the signals through the conductors;

means for detecting first and second resultant electrical signals flowing through the conductors as a result of the interaction of the first and second electrical signals with the remotely located resistance module; and

means for determining from the first and second resultant electrical signals the value of the first resistor contained in the resistance module.

49. A telemeter according to claim 19, wherein:

the means for alternately generating first and second electrical signals of opposite polarity includes means for alternately generating first and second square wave electrical signals of opposite polarity; and

the means for regulating the first and second electrical signals includes a shunt regulator coupled to the output of the square wave means for regulating the absolute magnitude of the current of each of the first and second electrical signals.

50. A telemeter according to claim 49 wherein the shunt regulator includes:

a Zener diode connected in a bridge circuit so that it operates bidirectionly and provides a reference voltage;

a resistance in series with the two conductors for providing a transistor biasing voltage; and

a bidirectional transistor circuit connected in series with the reference voltage meAns and connected across the two conductors for shunting current responsive to the reference voltage and the transistor biasing voltage to maintain a constant current through the two conductors.

51. A telemeter according to claim 37, wherein:

the means for alternately generating first and second electrical signals includes means for alternately generating first and second square wave electrical signals of opposite polarity; and

the means for regulating the first and second electrical signals includes a shunt regulator coupled to the output of the square wave means for regulating the absolute magnitude of the current of each of the first and second electrical signals.

52. A telemeter according to claim 51 wherein the shunt regulator includes:

a Zener diode connected in a bridge circuit so that it operates bidirectionly and provides a reference voltage;

a resistance in series with the two conductors for providing a transistor biasing voltage; and

a bidirectional transistor circuit connected in series with the reference voltage means and connected across the two conductors for shunting current responsive to the reference voltage and the transistor biasing voltage to maintain a constant current through the two conductors.

53. A telemeter according to claim 37 wherein the means for determining from the voltage components of the first and second resultant electrical signals the value of the resistance source includes:

first and second RC networks, the capacitances of the two RC networks being commonly connected;

first diode means for applying the voltage component of the first resultant electrical signals across the first RC network;

second diode means for applying the voltage component of the second resultant electrical signal across the second RC network;

each RC network having a relatively long time constant whereby the capacitance of the first RC network will remain charged until the capacitance of the second RC network is charged;

voltage divider means coupled to the output of the two commonly connected capacitances; and

means for measuring the difference between the charges on the two capacitances coupled to the output of the voltage divider means.

54. A method of determining the value of a remotely located electrical quantity whereby the electrical quantity and the determining apparatus need be connected only with two ordinary electrical conductors and the resistance of the two conductors does not produce error in the determination, and whereby no power source need be located at the electrical quantity, including the steps of:

applying alternately and individually first and second equal electrical signals of opposite polarity through the two conductors whereby at least one of the first and second electrical signals is applied to the electrical quantity to be measured;

maintaining constant one of the electrical parameters of current and voltage of each of the first and second electrical signals during said application of the first and second electrical signals;

detecting the other one of the electrical parameters of current and voltage resulting in the two conductors from said application of the first and second electrical signals; and

determining from said detected parameter the value of the electrical quantity to be measured.

55. A method of determining the value of a remotely located electrical quantity according to claim 52, wherein the step of determining from the detected parameter the value of the electrical quantity to be measured includes the step of:

determining the difference between the values of the detected parameter of voltage and current resulting from said application of the first and second electrical signals.

56. A method of determining the value of a remotely located electrical quantity according to claim 52, wherein the step of determining from the detected parameter the value of the electrical quantity to be measured includes the step of:

inteGrating the algebraic sum of the detected parameter of voltage and current resulting from said application of the first and second electrical signals.

57. A method of determining the value of a remotely located electrical quantity according to claim 52 wherein the step of alternately and individually applying the first and second equal electrical signals through a pair of conductors connecting with the electrical quantity to be measured includes the step of:

applying one of the first and second electrical signals to the electrical quantity to be measured and the other of the first and second electrical signals through a secondary reference device in parallel with the electrical quantity to be measured.

58. A method of determining the value of a remotely located electrical quantity according to claim 57 wherein the step of applying one of the first and second electrical signals through the electrical quantity to be measured and the other of the first and second electrical signals through a secondary reference device includes the step of:

routing the first and second electrical signals by unidirectional current means in series with the electrical quantity being measured and with the secondary reference device, respectively.

59. The method of determining the value of a remotely located electrical quantity according to claim 52 wherein the step of individually applying first and second equal electrical signals through the pair of conductors connecting with the electrical quantity to be measured includes the step of:

applying both the first and second electrical signals through the electrical quantity to be measured.

60. A method of determining the value of a remotely located electrical quantity according to claim 52 wherein the step of maintaining one of the electrical parameters of current and voltage constant during the application of the first and second electrical signals to the pair of conductors includes the step of:

maintaining the current of each of the first and second electrical signals constant while permitting the voltage of such signals to vary; and

the detecting step includes detecting the varying voltage resulting from the first and second electrical signals being applied to the two conductors and at least one of the first and second electrical signals being applied to the electrical quantity to be measured.