مرکز منطقه ای اطلاع رساني علوم و فناوري - A new principle for fast DC-sensitive potential-independent current comparators

Abstract :

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 oscillations $g(t)$ . 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 oscillations $g(t)$ are perfectly symmetrical in the sense that $g(t+T/2) = -g(t)$ . Here $g$ represents either the coil flux φ, the current $i$ or the voltage $u$ . The time is $t$ and $T$ the 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 oscillating $q(t)$ 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.