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A new principle for fast DC-sensitive potential-independent current comparators

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1 Author(s)
Marek, A. ; Brown Boveri Research Center, Switzerland

A new principle of operation makes feasible small, cheap potential-independent current comparators whose performance reaches or exceeds the best properties of bulky magnetic amplifiers of the second-harmonic type. Connection of a ferrite-core coil in parallel with a suitable negative resistance generates relaxation oscillationsg(t). Inherently, at large oscillations the coil (i,phi)- characteristic is perfectly symmetric about the origin:phi(-i) = -phi(i). Provided that the negative-resistance (i,u)- characteristic has the same symmetry:i(-u) = -i(u), the oscillationsg(t)are perfectly symmetrical in the sense thatg(t+T/2) = -g(t). Heregrepresents either the coil flux φ, the currentior the voltageu. The time istandTthe oscillation period. External magnetomotive force shifts the coil (i,phi)-characteristics, invalidating (1) and therefore (3). Consequently, the deviation from 50% duty-ratio of the oscillatingq(t)is a sensitive and extremely stable measure of this MMF. Neither core temperature, pressure nor magnetic creep cause any zero drift. Orders of magnitude reached experimentally are: Short-time zero instability and noise:leq 10^{-5}ampere-turn, time resolution:leq 10^{-4}s, zero drift from -70 to +100°C:< 10^{-4}ampere-turn.

Published in:

Magnetics, IEEE Transactions on  (Volume:13 ,  Issue: 5 )

Date of Publication:

Sep 1977

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