Patent GB-748782-A (GB)
Title: Apparatus for displaying and re-recording reproducible records of transient waveforms
Inventor: LOPER GEORGE BERNARD
IPC: G01V1/34
Filed: 1953-06-09
Abstract: 748,782. Transient recording and measuring; frequency analysis of complex oscillations; cathode ray oscillographs. SOCONY MOBIL OIL CO., Inc., [formerly SOCONY - VACUUM OIL CO., Inc.]. June 9, 1953, No. 15874/53. Class 37. [Also in Groups XXXVIII, XL (b) and XL (c)] In apparatus for study and analysis of transient waves derived in seismic exploration by .generation of an explosion impulse at the earth's surface and the reflection of shock waves from subterranean strata interfaces back to plural detecting stations at the surface, a variable density record of plural reflected transient waves against a constant frequency recorded timing scale superimposed with a timing marker corresponding to the instant of explosion is continuously reproduced to generate a first electrical signal from the transient wave, a second electrical signal from the timing marker, and a third electrical signal representing the timing scale, and there is provided an oscilloscope deflected along one axis by a cyclically selected first electrical signal and deflected along another axis by a sweep generator triggered by a manually adjustable electronic counter responsive to the second and third signals to display for examination a selected portion of the cyclically selected first signal waveform, displaced by a predetermined time interval from the instant of explosion, whereby filters may be individually adjusted to modify the several transient waves which are then re-recorded against a timing marker for further study. In Fig. 1, the six traces 11 recorded on a photographic film 10 by a variable density process represent seismic signals received at corresponding receiving stations linearly spaced over the earth's surface in response to the explosion of a surface charge at a time instant represented by marker 12 on trace 12a recording a constant frequency timing signal 30, whereby the time for energy to travel from the sender to each receiver through the earth with reflection from subsoil strata may be determined according to known practice by seismic analysis of the recorded traces. The recorded film is looped continuously and traversed between rollers 45, 46 and the traces are illuminated by light source 15 and corresponding photocells in unit 14 produce varying signal voltages corresponding to the recorded seismic signals which are connected through amplifying signal channels 20-25 which may be of the kind described in Specification 732,188, [Group XXXVIII], containing individually adjustable filters to a known multi-circuit electronic switch 26 for cyclically selecting individual signals for display by C.R. oscillograph 27 and to a conventional re-recorder 40 energized by the individual signals after modification by the appropriate filter amplifiers to produce a record of optimum clarity and resolution for detailed study. The compound signal derived from the photo-cell responsive to the explosion marker 12 superimposed on the timing signal 30 of a constant frequency of e.g. 1 kc/s. is applied to a selector circuit 32 comprising a low-pass filter 102 (Fig. 2) responsive thereto which supplies the input of a gating circuit 36 comprising resistance capacitance pulse-shaping stages 106 to 109 of which stage 107 is normally biased to cut off, which produces at its output 37 a train of differentiated positive pulses recurring at 1000 c.p.s., coupled to the input bus-bar 140 of a ring electronic counter (Fig. 3). The marker and timing signals together are amplified by triode 116 whose anode filter 117 rejects the timing signal and passes the marker signal to turn over a bi-stable multivibrator 34 comprising triodes 118, 119 having common cathodes grounded through R-C circuit 120, anodes connected to H.T. supply through resistors 123, and grids and anodes respectively interconnected by R-C circuits 121, 122. Triode 119 normally conducts and triode 118 is normally cut off so that the grid of triode 126 having a common cathode resistor 127 with triode 106 of the gate 36 is driven positive over R-C circuit 125 to cut off triode 106 and close the gate. Turnover of the multivibrator on arrival of the marker pulse opens the gate so that 1000 c.p.s. pips are applied to bus-bar 140 of ring counter 38a (Fig. 3) of counter unit 38 (Fig. 1) which comprises bi-grid thyratrons 130, 135, 143, 144 ... 146 having their anodes connected to an H.T. source, their cathodes grounded through resistors and the grid of each tube connected over a resistor to the shield grid of the next tube in succession, which shield is connected over a resistor to a negative bias source and over a condenser to the bus-bar 140. The control grid of each tube is connected directly to its cathode and to a respective contact of a 10-way switch 150 and the cathodes of successive tubes are interconnected by condensers. Assuming tube 130 is fired, a pip of the timing pulse train on bus-bar 140 causes tube 134 to fire, and its cathode potential to rise and drive the cathode potential of the preceding tube 130 still further positive over the coupling condenser, thus extinguishing tube 130. Succeeding pips fire successive tubes and extinguish preceding ones indefinitely so long as the 1000 p.p.s. train is supplied, and the arm of switch 150 derives from the cathode of the selected tube a 100 p.p.s. train which is applied through resistor 151 and rectifier 151a to a pulseshaping circuit comprising a monostable multivibrator, whose 100 p.p.s. output is applied similarly to operate a ring counter 38b having a cathode selector switch 150a which in turn derives a 10 p.p.s. signal to operate ring counter 38c over pulse-shaping circuit 182 so that cathode selector switch 150b derives a 1 p.p.s. signal to operate a final ring counter 38d, whose resultant 0.1 p.p.s. train triggers the sweep of oscillograph 27 at any selected instant whose time displacement after generation of the initial marker pulse is determined by the setting of switches 150, 150a, 150b as an integral multiple of one millisecond up to a maximum of 10 sees. Following one cycle of scanning of the recorded film, the gate 36 is closed and the ring counters reset to their starting position by developing a differentiated negative-going pulse from the horizontal deflection voltage at the end of each sweep which is applied over conductor 50 to turn over the multivibrator 34 (Fig. 2) whereby tube 118 is cut off and tube 119 conducts. Gate 36 correspondingly closes by reason of the bias developed across resistor 127, while the positivegoing pulse from anode of tube 118 is applied over condenser 162a to the grid of thyratron 163 of reset circuit 52, whose cathode is grounded and whose anode is connected to an H.T. line 165 over load resistor 166 and over resistor 172 and RC circuit 172a to the grid of triode 170. The junction of 172, 172a is grounded through a neon tube 173, the cathode of 170 is grounded direct, and its anode is connected to H.T. line 165 over a load resistor and through condenser 170a to the negatively biased anode of a diode 171 whose cathode is connected over resistance 174 to the shield grid of tube 130 of ring counter 38a (Fig. 3) intended to fire first. The shield grids of similar tubes 130a, 130b of the succeeding ring counters 38b, 38c are connected through diodes 171a, 171b to condenser 170a. The H.T. line of the several ring counters is energized from the voltage developed across the series R-C circuit 168 through which the anode of thyratron 163 is grounded, which fires on restoration of multivibrator 118, 119, discharging condenser 163a and reducing the H.T. voltage on the ring counters to extinguish the tubes thereof, after which tube 163 is extinguished and the condenser recharges, allowing H.T. to be again applied to the ring counter tubes. After a time delay equal or greater than the recovery time of tube 163 imposed by circuit 172a and condenser 173a, the negativegoing anode pulse due to firing of tube 163 develops a positive-going pulse on the anode of triode 170 which fires the first tubes 130, 130a, 130b of the ring counters in preparation for the initiation of the succeeding record cycle by the arrival of the initial marker pulse. False operation due to pulses arising at point 168 from the successive firing of the ring counter tubes is prevented by neon tube 173 and its parallel condenser 173a. While tube 163 is non-conducting and the ring counters are running, the neon tube is fired from the H.T. line over resistors 172, 166 and it shunts the unwanted pulses at point 168 to ground, but when tube 163 fires the neon tube voltage falls and it is extinguished to allow the application of the negative-going reset pulse to the grid of triode 170. Blanking pulses may be derived from the ring counting circuit 38c to extinguish the oscillograph beam at 0.1 sec. intervals to give a time scale on the display, or the blanking pulses may be derived from an additional series of ring counting circuits operated from the initial timing pulse to give an adjustable time scale. The sweep trigger pulse may be applied to the anode of tube 118 (Fig. 2) to reset the system at the beginning of a display sweep instead of at the end. The electronic switch 26 referred to above may be eliminated by the use of a multi-gun oscillograph to accommodate simultaneously all the recorded trace signals. The foregoing arrangement enables a chosen portion of each recorded trace to be successively displayed by the oscillograph on an expanded time scale for inspection and adjustment of the filters of amplifiers 20-25 (Fig. 1) to obtain a modified signal of optimum character for seismic analysis which may then be rerecorded by the secondary recorder 40, which also records a reference timing trace in response to the 100 p.p.s. train from ring counter circuit 38a on line 180 and the 10 p.p.s. train from ring counter circuit 38b on line 181, when the switches 150, 150a thereof have be