GB1278108A - Video surveillance system, recorder and method - Google Patents

Abstract

1278108 Video recording MINNESOTA MINING & MFG CO 12 Aug 1969 [13 Aug 1968] 40319/69 Heading H4F A video recording system is arranged so that only every nth field is recorded on a recording medium which is moved past a rotating transducing head at 1/nth of the normal playback speed. The system may be used for surveillance. The recording mode is illustrated in Fig. 1 in which the video outputs of two cameras are gated under control of a timing circuit and recorded on a magnetic tape video recorder having a rotating head by means of which successive fields are recorded on oblique tracks. The recorder is provided with a low speed tape transport motor 108 which is clutched to the normal drive motor 112 during recording to advance the tape at a slow speed. The video signal gates are controlled so that one complete field is recorded on each oblique track. A sync. signal is recorded along the edge of the tape by means of head 42 and a servo system is provided for controlling the transducer rotation. In the replay mode, Fig. 2, the normal motor is used to move the tape past the head and a conventional replay system is used except that the transducer rotation is synchronized by means of signals derived from a video drum pulse head 144 which is nearly 180 degrees out of phase with the output of the normal servo drum pulse head 54. The resulting phase displacement of about half a track width corrects for the change of skew of the oblique tracks due to their being recorded with the tape running at a low speed. In an example a recorder with a normal tape speed of 7¢ i.p.s. is operated in the recording mode at a tape speed of # i.p.s. and every 60th field is recorded (i.e. one field per second). A stop motion facility is provided, the tape drive being stopped and the transducer head drive being synchronized from a 60 Hz source. A suitable gating circuit for the video signal is described with reference to Fig. 3 (not shown) by means of which selected complete fields are passed to the video recording head under control of a timing circuit and of the vertical sync. pulses. The low speed motor drives the normal motor during recording and this latter motor generates a signal which can be utilized to provide timing pulses for the gating circuit, Fig. 4 (not shown). A circuit for gating alternately two camera signals so that they are recorded on alternate oblique tracks is described, Fig. 5 (not shown).