Electric power conversion systems – Current conversion – Including automatic or integral protection means
Patent
1999-07-01
2000-02-29
Wong, Peter S.
Electric power conversion systems
Current conversion
Including automatic or integral protection means
363 17, 363 98, 363131, H02H 7122, H02M 3335, H02M 324
Patent
active
06031740&
ABSTRACT:
This method completely eliminates the detrimental effect of eddy currents on the rise time of the magnetic field, so that it reaches its constant value already when the current assumes its maximum. The field is generated by a current flowing in a coil which forms part of a magnetic system contained in an electromagnetic flow sensor, which comprises a core and/or a pole piece. The current changes periodically its polarity thereby causing the eddy currents. The current flows in a H network of transistors (13, 14, 14, 16) or a T network of switching transistors (25, 26). A resistor (10, 10'; 22, 22') is series connected to the H or T network. In each current half-cycle, an initial voltage during a rise time of the current--as a first subcycle--which is higher than a final voltage during a second subcycle is fed to the coil. The voltage drop across the resistor is used to maintain the final voltage constant for forming the first and second final current values, and to compensate for the effect of the eddy currents. To do so, in each half-cycle the voltage drop across the resistor after the maximum of the coil current until the attainment of the final current is sampled at least three times in succession to form a correction quantity for the voltage across the H or T network in the next half-cycle.
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Endress & Hauser Flowtec AG
Vu Bao Q.
Wong Peter S.
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