Current regulator for loop powered time of flight and level measurement systems
AssigneeSiemens Milltronics Process Instruments, Inc.
InventorGeorge Quinton Lyon
Life of this patent
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Abstract
A protection circuit for a current loop powered level measurement or time of flight ranging apparatus. The protection circuit includes one or more Zener diodes, a leakage current detector circuit and a compensating current circuit. The leakage current detector circuit detects the leakage currents flowing from the Zener diodes and generates an output for the compensating current circuit. The compensating current circuit generates a compensating current so that the sum of the leakage currents and the compensating current remains a constant and the loop current is not affected by variations in the leakage currents for example as a result of variations in the voltage in the current loop or temperature of the device.
Claims19
A level measurement system, said level measurement system being powered by a two wire loop, said level measurement system comprising:
- (a) a transducer for emitting energy pulses and detecting reflected energy pulses;
- (b) a controller having a component for controlling said transducer, and a component for determining a level measurement based on the time of flight of said reflected energy pulse;
- (c) a power supply having an input port for receiving power from the loop, and a circuit for producing an output voltage;
- (d) a protection circuit, said protection circuit being coupled to the two wire loop and including one or more protection diodes and a current regulator circuit, said current regulator circuit generating a constant current output for the two wire loop, and including a detector circuit coupled to said one or more protection diodes for detecting a leakage signal corresponding to leakage current flowing in said one or more protection diodes, and said current regulator including a compensator circuit, said compensator circuit having an input for receiving said signal and a circuit for generating a variable current signal based on said signal, said variable current having a magnitude for maintaining said constant current output.
A level measurement apparatus, said level measurement apparatus being powered by a current loop, said level measurement apparatus comprising:
- (a) a transducer for emitting energy pulses and detecting reflected energy pulses:
- (b) a controller having a component for controlling said transducer, and a component for determining a level measurement based on the time of flight of said reflected energy pulse;
- (c) a power supply coupled to the current loop for generating circuit power in the level measurement apparatus;
- (d) a protection circuit coupled to the two wire loop at an input terminal and a return terminal, said protection circuit including one or more Zener diodes, a leakage current detector circuit and a compensating current circuit, said leakage current detector circuit being coupled to said Zener diodes and including a component for generating a sensed voltage in response to leakage currents from said Zener diodes, and said compensating current circuit having an input for receiving said sensed voltage and another input for receiving a reference voltage, said compensating circuit including a component for generating a compensating current based on said sensed voltage and said reference voltage, and said compensating current and said leakage currents generating a constant current for the two wire loop.
A level measurement apparatus, said level measurement apparatus being powered by a two wire loop, said level measurement apparatus comprising:
- means for emitting energy pulses and detecting reflected energy pulses;
- means for controlling a transducer, and means for determining a level measurement based on the time of flight of said reflected energy pulse;
- means for protecting coupled to the two wire loop at an input terminal and at a return terminal, said means for protecting including one or more Zener diodes, means for detecting leakage current and means for generating a compensating current, said means for detecting leakage current being coupled to said Zener diodes and including means for generating a sensed voltage in response to leakage currents from said Zener diodes, means for generating a reference voltage, and said means for generating a compensating current having an input for receiving said sensed voltage and another input for receiving said reference voltage, said means for generating a compensating current including a component for generating a compensating current based on said sensed voltage and said reference voltage, and said compensating current and said leakage currents forming a constant current for the two wire loop.
Dependencies are inferred from the claim text.