GB1263471A - Improvements in or relating to data recording - Google Patents

Abstract

1,263,471. Digital information recording system. PLESSEY CO. Ltd. 7 Feb., 1969 [16 Feb., 1968], No. 7836/68. Heading G5R. In a digital information incremental recording arrangement the information recorded in each tape channel is immediately checked by playback and comparison with the information required to be recorded in that channel. Each recording head 2 and playback head 3 form a single unit and the reluctance of the playback head is increased by a large non-magnetic gap 11 which reduces the direct pick-up of the recording signal in the playback head circuit. The information to be recorded is applied to a store 15 and controls a gate 16 feeding clock pulses from generator 17 to a bi-stable switch 18 which controls a write amplifier 19. These circuits include conventional apparatus for writing on tape using the NRZI system and the recording takes place when the tape is stationary. During forward movement of the tape to the next incremental position the recorded signal produces an output from the playback head which is amplified, 20, and then passed via a gate circuit 27 to a full wave rectifier and thence to a voltage level detector 22. The level detector output is passed via a second gate 23 to a bi-stable switch 24 and thence to a comparator 25 which compares the signal with that stored in unit 15. The output from the comparator is supplied via a gate 32 to indicate any error at output 26. The gates, which are energized by delayed clock pulses, serve to ensure that the direct record signal and other extraneous signals caused, e.g. by braking of the tape are excluded from the played-back signal and that the comparator is correctly sampled. A similar checking arrangement is provided for each tape channel. Incremental step length can be controlled by using the playedback signal to control the point at which the tape is stopped for the next bit to be written.