Patent GB-950193-A (GB)
Abstract: 950,193. Photo-electric investigation of variable records. SEISMOGRAPH SERVICE CORPORATION. May 24, 1960 [June 11, 1959], No. 18359/60. Heading G1A. [Also in Divisions F2, G3, G5 and H4] Relates to apparatus for developing seismic signals from a variable-amplitude oscillographic kind of record originally produced as a plurality of side-by-side seismic traces by recording signals arriving at geophones spaced from a seismic wave source and for recording the developed signals side-by-side on a magnetizable recording medium, the apparatus utilizing a rotatable drum for supporting the variable amplitude record and means for driving the recording medium simultaneously with the drum and the apparatus including follower means for tracking the traces of the variable amplitude record to develop corresponding electrical signals and for re-recording those signals as a plurality of side-by-side channels on the recording means. According to the invention the apparatus includes means driven simultaneously with the drum so as to introduce dynamic-error corrections, means introducing static-error corrections, and means for playing back the channels and recording the ensuing signals in visible form on a light-sensitive medium. The embodiment described incorporates means to provide timing marks on the re-recordings at equi-spaced intervals, and means to compensate for (1) differing recording speeds of the original records (2) speed variations during original recording and (3) for differential paper shrinkage between original records and between different areas thereof. Means are also provided for playback, at a higher speed than during recording, the channels on the magnetic record one-by-one or simultaneously and re-recording the signals on the light-sensitive medium after filtering and, if desired compositing. Additionally, the original record is aligned with the follower means at the end of each trace, in preparation for re-recording of the subsequent trace,by summing the speed corrections of the original-record drum introduced during the following of each trace. General arrangements, Fig. 1. The original record 24 is mounted on drum 21 which is driven from motor 70 via clutch and gear unit 72, differential gear 87 for inserting dynamic-error corrections from motor 95, and differential gear 90 for inserting corrections for differing and non-linear timing marks 25 and operated by a comparison of the phases of the outputs of photo-cells 115 and 123. The output of potentiometer 30 is fed via signal record/time-line switch 38 and amplifier 39 to switches 56 and 58 which permit a choice between the re-recording &c. functions outlined above. Re-recording drums 22 and 23 are driven together from motor 70 via differential gear 74 into which static-error corrections are set manually by control 79. The geophone-spread component of dynamic error is set into circuit 101 manually by control 102 and the component arising from variation of seismic wave velocity with depth ("velocity function") is set in by a cam-follower 106. A galvanometer cross-section record on lightsensitive medium 22a is afforded by light source 43 and coil and mirror 45 and a variable-density cross-section record by lamp 53 whose intensity is varied by the signals from amplifier 39. During simultaneous magnetic and light-sensitive recording the latter is used as a visual monitor of correct operation of the apparatus. Prony brakes are fitted to shafts 26 and 77. Photo-electric curve following, Figs. 2 and 3. The centre of a trace 24 is tracked by employing a pair of photoconductive cells 137, 138 with their circuit outputs connected in a balanced circuit 36 which develops no output signal when equal light reaches the cells; it is stated that this arrangement avoids hunting. The light source may be between the cells, or light sources may be disposed in the cell position shown with the cells in the centre of carriage 134. In either case the arrangement is such that the focal points of the cells are disposed on opposite sides of the trace to be followed. Belt drive 142 is clamped to an arm 147 to translate the carriage and actuate limit switches 148, 149. Shaft 140 may be turned manually to cater for crossing and tangential traces. Gear 153 is connected to potentiometer 30, Fig. 1. The servomotor control circuit 36 includes a potentiometer 174 for balancing the inputs to D.C. amplifier 175 which has gain-balancing potentiometers 176, 177 and anti-hunt networks 178. . .181 the outputs from which are applied to a sensing network 182 the latter being supplied with A.C. from a source supplying servomotor reference winding 150 via capacitor 189 which introduces a phase shift to achieve maximum motor speed. Amplifier 197 feeds motor control windings 198, 199. Timing correction and timing marker generation, Figs.4 and 5. Photo-cell 123 Fig.4, output is filtered to remove harmonics and amplifier 116 produces an output signal of one polarity when blocking oscillator 206 pulse leads the point of positive-to-negative swing of the sine-wave and of reverse polarity when there is lag. Photo-cell 115 Fig.5, is connected to a differentiating circuit 298, 209 and a current limiting resistor 213 is provided. Diode 215 eliminates negative-going excursions at blocking oscillator 206 input. Square reference pulses originating in photo-cell 123 circuit are filtered by circuits 228, 229 and 234, 235 and the fundamental frequency voltage and blocking oscillator pulses are fed to transistor 218 circuit which includes diodes 239, 240. Potentiometer 250 is adjusted for equal outputs across resistors 251, 252 when the blocking oscillator pulse occurs at the positive-to-negative zero cross-over point of the sine wave at amplifier 203 output. If the pulse occurs on the positive portion of the sine wave capacitor 243 is charged to a higher positive potential and a correspondingly increased voltage appears across resistor 251. The outputs at the wipers of potentiometers 255, 256 are fed via playback-record relay 259 to amplifier 116 to cause the associated servo-motor to retard or advance drum 21 for coincidence between the record timing marks and the reference signal. The motor also drives wiper 343 of potentiometer 345 connected in circuit 130 which includes a zeroing potentiometer 344 and at the end of a recording cycle the net total correction is applied via contacts of relay 259 to amplifier 116 input to drive drum 21 to its zero position in readiness for the re-recording of the next trace. The reference signals produced by cell 123 are applied to blocking oscillator 298 to impress timing markers on the record media via contact 276b. When wiper 343 is driven beyond predetermined limits relay 353 is energized to light warning lamp 357 and to prevent further application of input signals to amplifier 116. Recording, Figs. 1, 5. Selectable-polarity tracking potentiometer 30 output is applied via L.P. filter 263 to recording amplifier 264, 275 which incorporates capacitor 274 to eliminate long-term voltage variations due to skewing of the traces on the record. To increase the frequency of reproduced signals during playback of the magnetic-record drum 23 is then driven at high speed. Dynamic-error correction, Figs. 1 and 8. Device 107 sets in the dynamic-error component arising from velocity variation with depth and comprises a flexible-tape cam 302 formed by radially-adjustable setting devices 301 each including a permanent magnet, Figs. 9 and 10 (neither shown) (see Division F2). The error component arising from geophone-shot spacing is set in manually, Fig. 7 (not shown). Power circuits, Fig. 1. Arrangements are provided for slow and rapid rotation by motor 70 and the selective actuation of electromagnetic clutches in unit 72, Figs. 6 and 11 (neither shown). Cam-operated micro switches 406,411,412,418 and 420 are included for effectively retaining associated function switches closed for one cycle of operation and then stopping motor 70. Specification 871,865 is referred to.