| 摘要 |
<p>PURPOSE:To detect the magnetic material coating part, leader part, etc., of a tape stably and accurately without any influence of temperature variation, variance in characteristics of elements, etc., by detecting whether a signal level outputted from a photodetection part exceeds a specific value or not, and taking a proper measure. CONSTITUTION:When the magnetic material coating part of the tape is positioned between an LED22 and a phototransistor 23, a transistor (TR)Q3 does not turn on by the emitter current of a TRQ1 at this time. Then, a specific voltage is developed at a point C and controlled to almost a specific level. Then, when the leader part of the tape comes to between them, the phototransistor 23 increases in the quantity of photodetection, so the TRQ3 turns on. Then, the current flowing to the LED22 increases to emit insenser light. In this case, variation in potential at a point D is delayed slightly by a resistance R10 and a capacitor C1 and supplied to a TRQ2. Further, the potential at a point C is brought under level control automatically, so there is no influence of characteristic variance of the LED22 and phototransistor 23 themselves, variations in characteristics with temperature, etc.</p> |
