Start up circuit for DC powered field instrument
First Claim
1. An industrial process control transmitter comprising:
- first and second power supply terminals;
first and second process control loop terminals;
an energy storage device coupled between the first and second power supply terminals;
a switching regulator circuit coupled to the energy storage device and comprising a regulated voltage output;
a sensor which is powered by the switching regulator circuit through the regulated voltage output for sensing a process variable;
a microprocessor coupled to the sensor for receiving the sensed process variable, wherein the microprocessor is powered by the switching regulator circuit through the regulated voltage output;
a memory which is coupled to the microprocessor and powered by the switching regulator circuit through the regulated voltage output;
a current control circuit coupled between the microprocessor and the first and second process control loop terminals for controlling a current through the first and second process control loop terminals under control of the microprocessor;
a variable impedance circuit coupled between the energy storage device and the first power supply terminal and having an impedance control input, a first current path with a first impedance and a second current path with a second impedance, wherein the second impedance is less than the first impedance and the second current path is selectively coupled in parallel with the first current path as a function of a voltage applied to the impedance control input; and
a voltage measurement circuit comprising a comparator having a first comparison input which is coupled to the energy storage device, a second comparison input which is coupled to the first power supply terminal, and a comparison output which is coupled to the impedance control input.
1 Assignment
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Accused Products
Abstract
A direct current (DC) powered process instrument start up circuit includes an energy storage device, a switching regulator circuit, a variable impedance circuit, and a voltage measurement circuit. The energy storage device is coupled between first and second power supply terminals. The switching regulator circuit is coupled to the energy storage device and has a regulated voltage output. The variable impedance circuit is coupled between the energy storage device and the first power supply terminal and has an impedance control input. The voltage measurement circuit has a measurement input coupled to the energy storage device and a measurement output coupled to the impedance control input.
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Citations
13 Claims
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1. An industrial process control transmitter comprising:
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first and second power supply terminals; first and second process control loop terminals; an energy storage device coupled between the first and second power supply terminals; a switching regulator circuit coupled to the energy storage device and comprising a regulated voltage output; a sensor which is powered by the switching regulator circuit through the regulated voltage output for sensing a process variable; a microprocessor coupled to the sensor for receiving the sensed process variable, wherein the microprocessor is powered by the switching regulator circuit through the regulated voltage output; a memory which is coupled to the microprocessor and powered by the switching regulator circuit through the regulated voltage output; a current control circuit coupled between the microprocessor and the first and second process control loop terminals for controlling a current through the first and second process control loop terminals under control of the microprocessor; a variable impedance circuit coupled between the energy storage device and the first power supply terminal and having an impedance control input, a first current path with a first impedance and a second current path with a second impedance, wherein the second impedance is less than the first impedance and the second current path is selectively coupled in parallel with the first current path as a function of a voltage applied to the impedance control input; and a voltage measurement circuit comprising a comparator having a first comparison input which is coupled to the energy storage device, a second comparison input which is coupled to the first power supply terminal, and a comparison output which is coupled to the impedance control input. - View Dependent Claims (2, 3, 4, 5)
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6. A direct current (DC) powered process instrument start up circuit comprising:
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first and second power supply terminals; an energy storage device coupled between the first and second power supply terminals; a switching regulator circuit coupled to the energy storage device and comprising a regulated voltage output; a variable impedance circuit coupled between the energy storage device and the first power supply terminal and having an impedance control input, a first current path with a first impedance and a second current path with a second impedance, wherein the second impedance is less than the first impedance and the second current path is selectively coupled in parallel with the first current path as a function of a voltage applied to the impedance control input; and a voltage measurement circuit having a comparator with a first comparison input which is coupled to the energy storage device, a second comparison input which is coupled to the first power supply terminal, and a comparison output which is coupled to the impedance control input. - View Dependent Claims (7, 8, 9, 10)
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11. A method of initiating power to a field mounted process instrument which includes an energy storage device and a voltage regulator, the method comprising:
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applying an input power to the field mounted process instrument; charging the energy storage device with the input power through a first impedance; measuring energy developed across the energy storage device and comparing the measured energy to a representation of the input power; charging the energy storage device with the input power through a second impedance that is lower than the first impedance, after the energy developed across the energy storage device reaches a predetermined level relative to the representation of the input power; and powering the voltage regulator after the energy developed across the energy storage device reaches the predetermined level. - View Dependent Claims (12)
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13. An industrial process control transmitter comprising:
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first and second power supply terminals; first and second process control loop terminals; an energy storage device coupled between the first and second power supply terminals; a switching regulator circuit coupled to the energy storage device and comprising a regulated voltage output; a sensor which is powered by the switching regulator circuit through the regulated voltage output for sensing a process variable; a microprocessor coupled to the sensor for receiving the sensed process variable, wherein the microprocessor is powered by the switching regulator circuit through the regulated voltage output; a memory which is coupled to the microprocessor and powered by the switching regulator circuit through the regulated voltage output; a current control circuit coupled between the microprocessor and the first and second process control loop terminals; means for varying an impedance between the energy storage device and the first power supply terminal as a function of an impedance control signal; and means for measuring a voltage across the energy storage device and for generating the impedance control signal as a function of a comparison between the measured voltage and a representation of a voltage on the first power supply terminal.
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Specification