| 摘要 |
<p>A D.C. current transformer (CT) (used to measure D.C.) comprising a common primary winding (B) and a pair of saturable magnetic cores (C1, C2) on which respective secondary windings (W1, W2) are wound and connected in opposite senses in series to a source of alternating e.m.f. (E1), is provided with phase-sensitive means (2) for determining the sense of the unknown D.C. (11) in the primary winding. The phase sensitive means periodically senses and integrates the voltage (V1 + V2) (whose waveform is the -45° to +45° portion of a sine wave) across at least one of the secondary windings. The sense of the integrated waveform depends on whether said voltage is initially positive or negative, and is determined by the sense of the unknown D.C. in the primary winding.</p><p>Preferably said voltage is sensed at each half cycle of said alternating e.m.f.</p> |
