Two-wire current transmitter employing a stabilized current source in one electrical circuit containing control means in series therewith for controlling a direct current amplifier contained in a parallel circuit

Claim 2

A current transmitter comprising a pair of current terminals, first and second circuits connected in parallel with each other and in series with said terminals so that the current flowing through said first and second circuits also flows through said terminals, said first circuit including a direct current amplifier and said second circuit including a single constant current source, circuit means connected in series with said source so that all of the current flowing through said single constant current source flows through said circuit means for producing an alternating current derived entirely from said current flowing through said constant current source, means connected to said alternating current means for controlling said alternating current means in accordance with the magnitude of a variable condition, and means connected to said alternating current means for controlling said direct current amplifier, whereby the current flowing through said terminals is representative of the value of said variable condition.

Claim 3

A current transmitter as set forth in claim 1 in which said alternating current means includes an oscillator and alternating current amplifier in parallel therewith, said means for controlling said alternating current means in accordance with a variable condition including a chopper connected between said oscillator and alternating current amplifier so that said oscillator drives said chopper and said alternating current amplifier amplifies the output from said chopper, said means for controlling said alternating current means controlling the current to said chopper so that the output therefrom to said alternating current amplifier is changed in response to any change in the magnitude of said variable condition.

Claim 4

A current transmittEr as set forth in claim 2 in which said means responsive to said alternating current means includes a demodulator connected between said alternating current amplifier and said direct current amplifier for controlling said direct current amplifier in accordance with the output from said demodulator.

Claim 5

A current transmitter as set forth in claim 1 in which said alternating current controlling means includes a resistance bridge having a temperature sensitive element therein.

Claim 6

A current transmitter comprising a pair of current terminals, first and second circuits connected in parallel with each other and in series with said terminals so that the current flowing through said first and second circuits also flows through said terminals, said first circuit including a direct current amplifier and said second circuit including a constant current source comprising first, second and third transistors, each transistor having a base, collector and emitter and said second and third transistors being of opposite conductivity type with respect to said first transistor, the emitters and collectors of said first and third transistors being connected in series to provide a first path, diode means and a temperature compensating resistance network, said diode means being connected to said first path between said first and third transistors and to said resistance network, the emitter and collector of said second transistor forming a second path in parallel with the emitter-collector path of said first transistor, the respective bases of said first and third transistors being connected to spaced points on said second path and the base of said second transistor being connected to a point between said first and third transistors in said first path, said first transistor providing a primary current path therethrough when conducting which continues through said diode means and compensating network, said current transmitter further including means connected in series with said source for producing an alternating current, means connected to said alternating current means for controlling said alternating current means in accordance with the magnitude of a variable condition, and means connected to said alternating current means for controlling said direct current amplifier, whereby the current flowing through said terminals is representative of the value of said variable condition.

Claim 7

A current transmitter comprising a pair of current terminals, first and second circuits connected in parallel with each other and in series with said terminals so that the current flowing through said first and second circuits also flows through said terminals, said first circuit including a direct current amplifier and said second circuit including a constant current source comprising first, second and third transistors, each transistor having a base, collector and emitter and said second and third transistors being of opposite conductivity type with respect to said first transistor, the emitters and collectors of said first and third transistors being connected in series to provide a first path, diode means and a temperature compensating resistance network, said diode means being connected to said first path between said first and third transistors and to said resistance network, the emitter and collector of said second transistor forming a second path in parallel with the emitter-collector path of said first transistor, the respective bases of said first and third transistors being connected to spaced points on said second path and the base of said second transistor being connected to a point between said first and third transistors in said first path, said first transistor providing a primary current path therethrough when conducting which continues through said diode means and compensating network, said current transmitter further including means connected in series with said source for producing an alternating current, means connected to said alternating current means for controlling said alternating current means in accordance with the magnitude of a variable condition, and means connected to said alternating current means for controlling said direct current amplifier, whereby the current flowing through said terminals is representative of the value of said variable condition.

Claim 8

A current transmitter comprising a pair of current terminals, first and second circuits connected in parallel with each other and in series with said terminals so that the current flowing through said first and second circuits also flows through said terminals, said first circuit including a direct current amplifier and said second circuit including a constant current source comprising first, second and third transistors, said second and third transistors being of NPN conductivity with said first transistor being of PNP conductivity and each transistor having an emitter, collector and base, diode means, the emitter of said first transistor being connected to one of said current terminals and the collector thereof being connected to one side of said diode means, a temperature compensating resistance network connected to the other side of said diode means to provide a primary current path through the emitter-collector of said first transistor when conductive, said diode means and said resistance network, means connected to the collector of said first transistor and to the base of said second transistor for initially rendering said second transistor conductive so as to cause said first transistor to conduct to provide said primary current path through said diode means and resistance network, the collector of said second transistor being connected to the said one current terminal and the emitter of said second transistor being connected to the junction of said diode means and said network, the base of said first transistor also being connected to said one current terminal, said second transistor providinG a secondary current path through its collector and emitter, said diode means and resistance network, the base of said third transistor being connected to the junction of said diode means and said network to render said third transistor responsive to the voltage at the junction of said diode means and network for reducing the amount of conduction of said third transistor through its collector-emitter path to reduce the total current through said source, said current transmitter further including means connected in series with said source for producing an alternating current, means connected to said alternating current means for controlling said alternating current means in accordance with the magnitude of a variable condition, and means connected to said alternating current means for controlling said direct current amplifier, whereby the current flowing through said terminals is representative of the value of said variable condition.

Claim 9

A current transmitter comprising a pair of current terminals, first and second circuits connected in parallel with each other and in series with said terminals so that the current flowing through said first and second circuits also flows through said terminals, said first circuit including a direct current amplifier and said second circuit including a constant current source comprising first, second and third transistors, said second and third transistors being of NPN conductivity with said first transistor being of PNP conductivity and each transistor having an emitter, collector and base, diode means, the emitter of said first transistor being connected to one of said current terminals and the collector thereof being connected to one side of said diode means, a temperature compensating resistance network connected to the other side of said diode means to provide a primary current path through the emitter-collector of said first transistor when conductive, said diode means and said resistance network, means connected to the collector of said first transistor and to the base of said second transistor for initially rendering said second transistor conductive so as to cause said first transistor to conduct to provide said primary current path through said diode means and resistance network, the collector of said second transistor being connected to the said one current terminal and the emitter of said second transistor being connected to the junction of said diode means and said network, the base of said first transistor also being connected to said one current terminal, said second transistor providinG a secondary current path through its collector and emitter, said diode means and resistance network, the base of said third transistor being connected to the junction of said diode means and said network to render said third transistor responsive to the voltage at the junction of said diode means and network for reducing the amount of conduction of said third transistor through its collector-emitter path to reduce the total current through said source, said current transmitter further including means connected in series with said source for producing an alternating current, means connected to said alternating current means for controlling said alternating current means in accordance with the magnitude of a variable condition, and means connected to said alternating current means for controlling said direct current amplifier, whereby the current flowing through said terminals is representative of the value of said variable condition.

Claim 10

A current transmitter as set forth in claim 6 in which said resistance network includes first, second and third resistors connected in series, a first thermistor in parallel with said first resistor and a second thermistor in parallel with said third resistor of said resistance network.

Claim 11

In a two-wire current transmitter, a constant current source having input and output junctions, the source comprising first, second and third transistors, each having a base, collector and emitter, diode means, a temperature compensating resistance network, the emitter of said first transistor being connected to said input junction and the collector thereof being connected to the anode side of said diode means, the cathode side of said diode means being connected to one side of said resistance network and the other side of said resistance network being connected to said output junction, a first resistor connected between the emitter and collector of said first transistor, a second resistor connected between the collector of said first transistor and the base of said second transistor and also to the collector of said third transistor, the emitter of said second transistor being connected to the junction of said diode means and network and also to the base of said third transistor, the emitter of said third transistor being connected to said output junction, a third resistor connected between the emitter of said first transistor and the base thereof, a fourth resistor connected between the base of said first transistor and the collector of said second transistor, whereby a primary current path exists through the emitter-collector of said first transistor, said diode means and said resistance network when said first transistor is conducting.

Claim 12

In a two-wire current transmitter, a constant current source having input and output junctions, the source comprising first, second and third transistors, each having a base, collector and emitter, diode means, a temperature compensating resistance network, the emitter of said first transistor being connected to said input junction and the collector thereof being connected to the anode side of said diode means, the cathode side of said diode means being connected to one side of said resistance network and the other side of said resistance network being connected to said output junction, a first resistor connected between the emitter and collector of said first transistor, a second resistor connected between the collector of said first transistor and the base of said second transistor and also to the collector of said third transistor, the emitter of said second transistor being connected to the junction of said diode means and network and also to the base of said third transistor, the emitter of said third transistor being connected to said output junction, a third resistor connected between the emitter of said first transistor and the base thereof, a fourth resistor connected between the base of said first transistor and the collector of said second transistor, whereby a primary current path exists through the emitter-collector of said first transistor, said diode means and said resistance network when said first transistor is conducting.

Claim 13

The combination of claim 8 in which said resistance network includes first, second and third serially connected resistors, a first thermistor connected in parallel with said first resistor and a second thermistor connected in parallel with said third resistor of said resistance network.

Claim 14

A current transmitter comprising a pair of current terminals, a direct current amplifier connected between said terminals through which amplifier a variable portion of the current flowing through said terminals passes and is controlled, a constant current source connected between said terminals and in parallel with said amplifier through which source a second portion of the current flows so as to be regulated thereby, a chopper drive and alternating current carrier amplifier connected in parallel with each other and in series with said current source, a chopper connected between said chopper drive and alternating current amplifier, a condition responsive bridge network for controlling said chopper in accordance with the magnitude of a variable condition, said bridge network being in series with said current source and in series with said alternating current amplifier to cause the current supplied by said current source to recombine with the current through said direct current amplifier, and a demodulator having iTs input connected to said alternating current carrier amplifier and its output connected to said direct current amplifier for controlling said direct current amplifier, whereby the current through said terminals will be indicative of the amount of variation occurring in the variable condition.

Claim 15

A current transmitter comprising a pair of current terminals, a direct current amplifier connected between said terminals through which amplifier a variable portion of the current flowing through said terminals passes and is controlled, a constant current source connected between said terminals and in parallel with said amplifier through which source a second portion of the current flows so as to be regulated thereby, a chopper drive and alternating current carrier amplifier connected in parallel with each other and in series with said current source, a chopper connected between said chopper drive and alternating current amplifier, a condition responsive bridge network for controlling said chopper in accordance with the magnitude of a variable condition, said bridge network being in series with said current source and in series with said alternating current amplifier to cause the current supplied by said current source to recombine with the current through said direct current amplifier, and a demodulator having iTs input connected to said alternating current carrier amplifier and its output connected to said direct current amplifier for controlling said direct current amplifier, whereby the current through said terminals will be indicative of the amount of variation occurring in the variable condition.

Claim 16

In a current transmitter, a constant current source having input and output junctions, the source comprising first, second and third transistors, each having a base, collector and emitter, diode means, a temperature responsive resistance network, the emitter of said first transistor being connected to said input junction and the collector thereof being connected to the anode side of said diode means, the cathode side of said diode means being connected to one side of said resistance network and the other side of said resistance network being connected to said output junction, a first resistor connected between the emitter and collector of said first transistor, a second resistor connected between the collector of said first transistor and the base of said second transistor and also to the collector of said third transistor, the emitter of said second transistor being connected to the junction of said diode means and network and also to the base of said third transistor, the emitter of said third transistor being connected to said output junction, whereby a primary current path exists through the emitter-collector of the first transistor, the diode means and said resistance network when said first transistor is conducting.

Claim 17

In a current transmitter, a constant current source having input and output junctions, the source comprising first, second and third transistors, each having a base, collector and emitter, diode means, a temperature responsive resistance network, the emitter of said first transistor being connected to said input junction and the collector thereof being connected to the anode side of said diode means, the cathode side of said diode means being connected to one side of said resistance network and the other side of said resistance network being connected to said output junction, a first resistor connected between the emitter and collector of said first transistor, a second resistor connected between the collector of said first transistor and the base of said second transistor and also to the collector of said third transistor, the emitter of said second transistor being connected to the junction of said diode means and network and also to the base of said third transistor, the emitter of said third transistor being connected to said output junction, whereby a primary current path exists through the emitter-collector of the first transistor, the diode means and said resistance network when said first transistor is conducting.

Claim 18

The combination of claim 11 in which said resistance network includes first, second and third serially connected resistors, a first thermistor connected in parallel with said first resistor and a second thermistor connected in parallel with said third resistor of said resistance network.

Claim 19

The combination set forth in claim 11 including means in series with said constant current source and energized solely thereby for providing a control signal in accordance with the magnitude of a variable condition, and a direct current amplifier in parallel with said constant current source and said means in series with said constant current source and connected to said constant current source so that said control signal controls said direct current amplifier.