| 摘要 |
<p>Four control units are connected in parallel with one another between a pair of conductors which are the cores of a light current carrying cable. Each unit is connected to the step switching equipment of a transformer, and also in each control unit, a resistance contact strip has its ends fed from a constant current source, which drives the current through the strip. A wiper arm is coupled to a step switching drive, and the position of the wiper arm corresponds in every case, to the position of the step switching equipment. The wiper arm, is also in series with two anti-parallel direction-dependant relays and an on/off switch which connects the arm to the main supply. When current flows through one or other relay, due to an imbalance, the appropriate relay contact closes and the wiper arm travels along the resistance strip until balance is restored.</p> |
