| 摘要 |
PURPOSE:To detect tape quantity quickly and properly at the time of starting of a travel by measuring a rotational frequency of a supplying reel in order to detect a remaining amount of a tape in a VTR. CONSTITUTION:A rotational pulse from a photosensor 6 is added to a waveform shaping circuit 21, and a shaped waveform is inputted to a microcomputer 22. On the other hand, a crystal oscillator 23 and an oscillator circuit 24 output a reference clock pulse, and input it to a pulse counter 25. The counter 25 is counting the number of pulses, and the microcomputer 22 reads an output (ci) of the counter 25 according to a timing (c) of a rise of a rotational pulse (a), calculates tape remaining time and indicates it on a display element 26. A certain rotational frequency Tk and the difference DELTATi between the Tk and the previous rotational frequency is calculated. The DELTATi is proportional to thickness of the tape. Thus whether or not the rotation of the reel is stable is decided depending upon the constant value of the DELTATi, and a remaining amount of the tape is detected quickly and with little errors at the time of starting of a travel of the tape, etc. |
