Patent GB-850779-A (GB)
Abstract: 850,779. Geophysical prospecting. GULF RESEARCH & DEVELOPMENT CO. Jan. 21, 1957 [Jan, 24, 1956], No. 2069/57. Class 40(7). [Also in Group XX] Apparatus for making a seismic profile from selected portions of a seismogram comprises means supporting a photographic medium on which the profile is to be made, a restricted light source, a carriage for holding an elongated transparent seismogram between said medium and said light source and in contact with said medium, means for moving said light source longitudinally with respect to said medium to expose the medium through selected portions of the seismogram, and controllable positioning means connected to said carriage adapted to effect transverse positioning of said carriage with respect to said medium-supporting means. In the form shown the seismogram 15, Fig. 3, carries records in adjacent parallel tracks, perpendicular to the plane of the drawing, each representing, as a function of time, the output of one of a number of geophones disposed at different distances from a shot point. Another track indicates the actual time of the shot and a timing trace is also included. The purpose of the apparatus is to print individual tracks from the seismogram on to the photographic film 21, the film being fed after each track has been printed and the seismogram being moved laterally by the "record advancing means" 43 to bring a fresh track into position for printing. The printing is effected by a lamp P22 in a housing 23, its light being reflected from a mirror through a slit 24 transverse to the track, the printing of the track being effected by longitudinal movement of the housing 23. A photo-cell in the lamphouse indicates the lamp brightness. During printing various corrections are required to be effected by relative longitudinal movement of the seismogram and film. These are the "fixed correction" which is the same for all events on any record track and can be introduced by an initial adjustment of the seismogram and film, and the "variable correction" which changes for different events on the track corresponding to reflections from different depths and requires a continuously changing relative adjustment of seismogram and film as the printing proceeds. The film magazine 26 shown in Fig. 3 is described in detail in Specification 850,780 together with the means by which successive equal amounts of film are fed over the roller 30. The magazine is mounted on rollers 57 which run on rails 58 carried on a shaft 59 rotatable by a motor P221 to facilitate the insertion and removal of the magazine in the apparatus shown in elevation in Fig. 6 and plan in Fig. 7. The seismogram 15 is mounted in a slot 77 in the plate 25 which is slidably mounted by brackets 79 on a transverse bar 67 carried on a main plate 68 on which the plate 25 is also carried by rollers 78. The "record advancing means" comprises a spring, not shown, secured to an anchorage 200 and controlled by an escapement mechanism comprising alternately energized solenoids. The plate 68 is supported by rollers 71, 72 and by brackets 69, 70, slidable on a bar 66. The plates 25, 68 carry racks 90, 83 which may be engaged by pinions operated by external handles 88, 86 for initial setting operations. The bar 66 also carries brackets 91, 92 on the carriage 93 for the printing lamp housing 23. The latter is supported by rollers 94 which provide a small clearance between the slit in the housing and the seismogram. Longitudinal movement of the housing 23 is effected by steel tapes 103, 104 passing over pulleys 226, 227 and wound in opposite directions on drums which may be rotated by a motor P206. The two tapes are attached to opposite ends of the carriage, the tape 103 passing over a pulley 225 and containing a tensioning spring 102. A flexible cable 110 is secured to a bushing 108, carried on a fixed transverse bar 107 and passes over a pulley 111 carried by the plate 68 on to a drum, not shown, also carried by the plate and rotatable by a motor. By winding the cable the plate is moved to the left against a spring 109 to apply the fixed correction. At the same time a carriage 100, supporting a stylus 556, moves along the plate 68 until the stylus senses a hole in a card 95, carried by the plate 25. The card is punched with a series of holes, one for each track in the seismogram, each hole representing, by its position, the amount of correction required, the hole appropriate to the track being printed being brought into line with the stylus by the transverse movement of the seismogram. The need for a variable correction arises largely from the obliquity of the reflected sound paths to geophones remote from the shot point. This correction is applied by a displacement of the bushing 108 on the bar 107. The cable 110 passes between pulleys 106 on the carriage 93 and the effect of such displacement increases with the passage of the printing lamp to the left corresponding to reflections from shallower horizons with consequent greater obliquity of sound path, the geometry of which is shown to be reproduced by the obliquity of the cable 110 between the rollers 106 and the bushing 108. The amounts of correction required for the various seismogram tracks to take account of obliquity effects are recorded as perforations on a card 96 sensed by a stylus 582 on a carriage 101. The mechanism for adjusting the bushing 108 is shown diagrammatically in Fig. 22. A lead screw 155 is rotated by a motor P208 and a selsyn transmitter P207 driven therefrom actuates a receiver P216 which drives the stylus carriage 101 the motor being stopped when the stylus senses a hole in the card. Rotation of the lead screw drives a carriage 156, the movement of which is communicated to the bushing 108. The mechanism shown, however, also applies a correction for the variation of the speed of sound with the depth from which a reflection is obtained. For this purpose the motor P206 also drives a cam 178 which actuates a follower plunger which rotates a member 172 about a point 171. The slot 173 in this member engages a follower 180 carried by a bushing 165 slidable on a bar 163 on the carriage 156. A cord 150 secured to the bushing 108 passes round pulleys 151, 152, 153, 154 on fixed axes and round pulleys 167, 168, 169, 170 on the carriage 156, its two ends being secured to the bushing 165. As a result the correction applied by the cam is multiplied by that applied by the motor P208 in response to the stylus 582 and the product added to the latter correction, the sum being applied, as is shown to be needed, to the bushing 108. A further correction to take account of slope of the ground surface is applied to the micrometer 99 which produces relative adjustment of the printing lamp house 23 and the carriage 93. The apparatus as above described is associated with a relay control circuit which provides for automatic printing of the various tracks on the record in sequence, the printing lamp being extinguished during its return strokes. Normally, each record carries 24 tracks and the whole or either half of those may be printed in forward or reverse sequence, each of the cards 95, 96 being scanned by its stylus to find the position of the perforation indicating the corrections required for the next track. Each may be printed once or twice in succession, or each may be printed in superposition with its predecessor. Any track may be skipped or a blank may be left in the printing. Numerous safety, interlocking and fault indicating devices are provided together with means for over-riding the automatic operation when special printing operations have to be performed.