Transducer for converting a varying reactance signal to a DC current signal
First Claim
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1. A two wire current transmitter for providing a direct current signal proportional to a condition to be measured comprising first and second terminals for connection to a direct current supply means;
- a resistance network connected to said first terminal;
a current controller in series with the resistance network and connected to said second terminal, said current controller comprising first means connected to the resistance network to provide a current shunt path between said resistance network and said second terminal, and amplifier means having an input and an output, said amplifier means output being coupled to said first means to control the current through said first means as a function of signals at said amplifier means input, and second means connected to said resistance network and said amplifier means to provide a signal at the input of said amplifier means which is a function of the current through said resistance network;
an input stage means connected between said first and second terminals including means defining at least two separate current paths, at least one of which is a regulated current path, and including a transducer to provide an electrical signal in response to a parameter to be measured, said input stage means being coupled to said resistance network and to said input of said amplifier means of the current controller and providing an excitation current to said transducer, a Zener diode connected in the regulated current path to provide a precise reference voltage across said Zener diode, a resistance voltage divider connected directly across said Zener diode, said resistance voltage divider having a voltage signal connection connected to said input of said amplifier means;
said current controller comprising means to regulate the current in said regulated current path comprising a transistor having a collector, an emitter and a base and being connected to transmit between its collector and emitter a portion of the current passing through said shunt path, and a resistor connected between the base and emitter of said transistor, the base of said transistor being connected to said regulated current path; and
said input stage means including fourth means to provide an output signal to the input of said amplifier means which is a function of the parameter to be measured, said amplifier means thereby adjusting current through said first means and said second means in response to the output signal of said input stage means.
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Abstract
A two wire current transmitter providing a current signal representing a parameter measured by a variable reactance transducer along the same two wires that are used to carry excitation power to the circuit. The reactance is measured by a circuit providing a DC signal which controls a current control stage to modify the total current through the two wires. The current control stage has a small number of components and operates on a relatively low voltage.
29 Citations
23 Claims
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1. A two wire current transmitter for providing a direct current signal proportional to a condition to be measured comprising first and second terminals for connection to a direct current supply means;
- a resistance network connected to said first terminal;
a current controller in series with the resistance network and connected to said second terminal, said current controller comprising first means connected to the resistance network to provide a current shunt path between said resistance network and said second terminal, and amplifier means having an input and an output, said amplifier means output being coupled to said first means to control the current through said first means as a function of signals at said amplifier means input, and second means connected to said resistance network and said amplifier means to provide a signal at the input of said amplifier means which is a function of the current through said resistance network;
an input stage means connected between said first and second terminals including means defining at least two separate current paths, at least one of which is a regulated current path, and including a transducer to provide an electrical signal in response to a parameter to be measured, said input stage means being coupled to said resistance network and to said input of said amplifier means of the current controller and providing an excitation current to said transducer, a Zener diode connected in the regulated current path to provide a precise reference voltage across said Zener diode, a resistance voltage divider connected directly across said Zener diode, said resistance voltage divider having a voltage signal connection connected to said input of said amplifier means;
said current controller comprising means to regulate the current in said regulated current path comprising a transistor having a collector, an emitter and a base and being connected to transmit between its collector and emitter a portion of the current passing through said shunt path, and a resistor connected between the base and emitter of said transistor, the base of said transistor being connected to said regulated current path; and
said input stage means including fourth means to provide an output signal to the input of said amplifier means which is a function of the parameter to be measured, said amplifier means thereby adjusting current through said first means and said second means in response to the output signal of said input stage means. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19)
- a resistance network connected to said first terminal;
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20. A two wire current transmitter for providing a direct current signal proportional to a condition to be measured comprising first and second terminals for connection to a direct current supply means;
- a series connected resistance network and a current controller connected between said first and second terminals, said current controller comprising first means connected to the resistance network to provide a current shunt path between said resistance network and said second terminal, and amplifier means having an input and an output, said amplifier means output being coupled to said first means to control the current through said shunt path as a function of a signal at said amplifier means input, and second means connected to said resistance network and said amplifier means to provide a signal at the input of said amplifier means which is a function of the current through said resistance network; and
signal input stage means coupled to said resistance network and said current controller, said input stage means comprising third means to provide a reference signal, a variable reactance transducer, and an oscillator;
said variable reactance transducer comprising a single variable capacitor having a capacitance value C1, a reference capacitor having a capacitance value C2, means coupling said oscillator to both of said capacitors to provide excitation current thereto, and fourth means connected to both of said capacitors to deliver a transducer output signal substantially proportional to the quantity (C2 /C1 -
1); and
fifth means coupled to the input stage means and to the input of said amplifier means to provide a variable signal to the input of said amplifier means which is a function of the transducer output signal and the reference signal, said amplifier means thereby adjusting current through said shunt path and said second means in response to said variable signal. - View Dependent Claims (21, 22, 23)
- a series connected resistance network and a current controller connected between said first and second terminals, said current controller comprising first means connected to the resistance network to provide a current shunt path between said resistance network and said second terminal, and amplifier means having an input and an output, said amplifier means output being coupled to said first means to control the current through said shunt path as a function of a signal at said amplifier means input, and second means connected to said resistance network and said amplifier means to provide a signal at the input of said amplifier means which is a function of the current through said resistance network; and
Specification