| 摘要 |
<p>PURPOSE:To detect both the termination and the travelling state of a tape, by forming a balanced bridge circuit with an internal resistance of a reel motor and three other resistances and then detecting the output existing between balanced points and proportional to the counter electromotive force which is generated by the revolution of the motor. CONSTITUTION:A bridge circuit 10 is formed with an internal resistance of a reel DC motor 1 and three other resistances 2, 3 and 4. The output terminals P and Q are fed to a differential amplifying circuit 5. The counter electromotive force is generated at the terminals P and Q in proportion to the speed of revolution of the motor 1. This output is differentially amplified 5 and then fed to comparators 6, 7 and 8. For reference voltages Vh, Vs and Ve which are set at the comparators 6-8, Vh>Ve>Vs is satisfied. Then an abnormal high speed and the stoppage of travelling are detected for a tape by comparators 6 and 7. At the same time, an abnormal low speed is detected by an AND of outputs of the comparators 8 and 7. As a result, both the termination and the abnormal travelling of the tape can be detected through a simple circuit.</p> |
