Electricity: measuring and testing – Measuring – testing – or sensing electricity – per se – Magnetic saturation
Reexamination Certificate
1998-09-16
2001-03-20
Snow, Walter E. (Department: 2862)
Electricity: measuring and testing
Measuring, testing, or sensing electricity, per se
Magnetic saturation
C324S225000, C338S03200R, C327S511000
Reexamination Certificate
active
06204657
ABSTRACT:
BACKGROUND OF THE INVENTION
Closed-loop Hall effect current transformers (CT) have been used and known for several years. For example, see U.S. Pat. No. 3,573,616, incorporated herein by reference. An excellent type of such closed loop CT is one with a good signal to noise ratio, in other words having a high signal output. Such a CT device can be made with indium antimony (InSb), but indium antimony is characterized by having poor linearity and a very strong negative temperature coefficient regarding its main terminal resistance.
SUMMARY OF THE INVENTION
This invention relates to a closed loop Hall effect CT and will have specific but not limited application to such a CT made with indium antimony.
CT devices with strong temperature coefficients of resistance are preferably driven from voltage sources if the voltage offset as compared to temperature can be minimized. Also, with a negative temperature coefficient, there is a risk of thermal runaway as the input power to the CT increases with temperature and the drive voltage is held constant. Thus it is necessary to limit the peak current which can be delivered to the CT device. In this invention a resistor is placed in series with a regulating amplifier which provides the drive voltage to the Hall effect device. The resistor is selected such that the amplifier will saturate before destructive current can be delivered to the Hall effect device. Observing the voltage drop across the resistor, the current drawn by the Hall effect device and thus its temperature can be monitored.
In a formulation and construction of Hall devices, there are small errors in both symmetry and homogeneity. These errors, while slight, will nevertheless cause drift with the resulting operational sequence controlled by the CT being in error. In this invention, a small fraction of the temperature signal across the series placed resistor associated with the regulating amplifier is mixed with the DC output signal from the Hall effect device so as to null the effect of the temperature dependent error signal in the device.
It is an object of this invention to provide a closed loop Hall effect CT having a high signal to noise ratio in which the operating temperature of the Hall effect device can be monitored without the need of an external temperature sensor.
It is another object of this invention to provide a closed loop Hall effect CT in which the offset of the drive voltage to the device caused by variations in temperature of the device can be substantially eliminated.
Other objects of this invention will become apparent upon a reading of the following description.
REFERENCES:
patent: 3573616 (1971-04-01), Kahen
patent: 5818225 (1998-10-01), Miekley et al.
Baker & Daniels
Crown Audio, Inc.
Snow Walter E.
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