Relating to tape transport control systems

A tape transport system comprising a control unit, a take-up motor for driving a take-up reel, a supply motor for driving a supply reel, and first and second pulse switched servo units coupling said control unit to said take-up motor and supply motor respectively, said pulse switched servo units each comprising an error device, a pulse width modulator for varying current to said associated motor, and a switching unit for reversing said motor current, the system further comprising a tape transfer sensing means for monitoring the length of tape transferred between said reels, a tape velocity sensing means for sensing deviations in velocity of said tape transfer from a predetermined required velocity, a take-up motor current sensing means and a supply motor current sensing means for sensing respectively deviations in take-up motor current and supply motor current from respective pre-determined motor currents, the control unit being arranged to evaluate respective selected current levels for the take-up and supply motors in response to signals received from said tape transfer sensing means, said error devices being arranged to generate correcting signals to correct said respective selected current levels, in dependence on said deviations sensed by said tape velocity sensing means or said respective motor current sensing means.