| 摘要 |
<p>PURPOSE:To provide a loop sensor which produces a presence output without requiring any additional drift correcting function. CONSTITUTION:In a loop sensor for detecting an object based on the variation of inductance of a loop conductor laid in the detecting region of the object, a cable 3 integrating a conductor 1 and a resistor wire 2 us laid in the detecting region and a rectangular wave signal having a predetermined period is fed from a second signal generator 9 to an analog switch 8 thus opening/closing the opposite ends of the resistor wire 2 alternately at a predetermined period. Variation of inductance of the conductor 1 due to the periodic closing/opening of the resistor wire 2 is extracted by a bridge circuit 6 and detected by a detecting circuit 12 before the level thereof is determined by a level determining circuit 13. Consequently, an AC output representative of presence of an object is generated when the variation of the detected output due to closing/opening of the resistor wire 2 is low, whereas a DC output representative of absence of object is generated when the variation is high.</p> |
