Metricom, Inc.

Timothy J Knutson

Paul Baran

Various combinations of three elements are disclosed for use in accurate measurement of power through current measurement over a wide dynamic range, namely, a current shunt which is preferably an isothermal current shunt, a current transformer, which is preferably a high initial permeability current transformer, and a low-impedance burden load, which in the preferred embodiment includes an active negative impedance element which causes the removal of the effects of excitation current by canceling secondary winding resistance of the current transformer. In a specific embodiment of an isothermal current shunt according to the invention, a very linear device is achieved by construction out of copper in such a manner that the poor resistance versus temperature coefficient of copper does not affect the accuracy of measurement. Specifically, the shunt is constructed in an unbalanced isothermal bridge configuration, so that heat-induced variations are suppressed. Further, a very small current transformer is used having a core optimized for high initial permeability.

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San Jose, CA, United States of America

Timothy J Knutson