GB1066472A - Improvements in and relating to the testing of magnetic recording tape - Google Patents

Abstract

1,066,472. Testing magnetic tape; counter circuits. BRITISH BROADCASTING CORPORATION. June 8, 1965 [May 7, 1964], No. 19102/64. Headings G4D and G5R. Test apparatus for determining the number of " drop out" regions in a magnetic tape i.e. the number of regions of the tape in which the magnetic recording material is absent from the support medium, comprises means for recording a constant amplitude signal on the tape e.g. a black level signal on a video tape, means for reproducing the signal with superimposed " drop out " pulses and means for recording the number of pulses produced and the number of times the pulse count per predetermined length of tape exceeds a set value. Each drop out pulses in the reproduced signal at the output of amplifier 12 triggers a monostable multivibrator 13 and the constant duration output pulses from the multivibrator are applied via a first path 14-18 including inhibit circuit 14 and " divide by ten " circuit 15 to a counter 19 which records in tens the number of drop out regions in the tape. The inhibit circuit is provided to close the path if due to some fault in the reproducing means spurious pulses are produced at a rate sufficient to charge capacitor 22 via emitter follower 20 and rectifier 21 to a value which triggers circuit 23. The output of the D.C. trigger circuit operates an alarm 27 in addition to closing the counting path. The pulses from amplifier 12 are also applied via amplifier 28 to a monostable multivibrator 29 which is connected to a " divide by eight " chain 30, 36, 37. This chain is associated with a free running multivibrator 32 which generates a signal each four seconds to return the chain to zero. If more than seven drop out regions are present in a length of the tape which takes four seconds to pass the transducer head an output signal is applied to a counter 47 and also to a circuit 43 which applies a mark on a cue track on the tape. Fig. 2 (not shown) indicates an arrangement whereby " drop out " pulses longer than a set duration are applied to multivibrator 13 and pulses longer than a much shorter duration are applied to multivibrator 29.