SU812194A3 - System for control of seismic vibrator - Google Patents

Abstract

1,153,975. Data storage arrangements. CONTINENTAL OIL CO. 10 Oct., 1967 [16 Nov. 1966], No. 46223/67. Heading G4C. [Also in Divisions G3 and H4] To eliminate equipment-induced timing errors in a waveform control signal for a seismic vibrator the signal, comprising a sequence of digital " words ", is placed in a buffer store and successive words are then read out from the store at a precisely controlled rate for application to a digital-to-analogue (D/A) converter and thence to the vibrator. In the Fig. 3 embodiment the control signal is computer-generated or derived from an analogue waveform by an analogue-to-digital converter and comprises digital samples (of a frequency sweep signal) in the form of sequentially recorded words, each word being two sequential " characters " of seven " bits " each, on magnetic tape 112. The seven bits are read in parallel by head 114 and applied to OR gate 120 to provide one clock pulse per character for driving shift register 124. These clock pulses, taken from one output of the shift register, are fed also to phase comparator 106 to provide an error signal for phase-locking the playback speed of tape 112 to a precision oscillator 90. Sequential outputs on lines 150-168 of register 124 open respective gates 130-148 to steer successive characters from playback amplifier 126 to an N-word buffer store 190-200 (e.g. comprising bi-stable circuits). The words are read out from the store by opening gates 212- 220 sequentially with pulses provided by shift register 222 at a precise rate controlled by oscillator 90. The readout rate is thus unaffected by wow and flutter in the tape playback process. The words from gates 212-220 are reconstituted as an analogue signal by D/A converter 98 and applied directly, or via a radio link 254, to the vibrator 18. This analogue signal may also be used in subsequent signal processing (e.g. correlation) of the output of a geophone array. As soon as a particular word has been read out from store the associated storage element is reset by an output from reset shift register 238 so that the storage element is freed for storing a further word from tape 112. If tape or other speed errors are large or have a long term drift a large buffer store is required and the store may then comprise magnetic cores or may be a random-access store of sufficient capacity to store the total digital sweep signal (in which case the tape record 112 is unnecessary). Details of the application of the individual data bits to the gates 130-148 and store 190- 200 are given (Fig. 4, not shown).

Description

(54) CONTROL SYSTEM FOR SEISMIC VIBRATOR

one ; . The invention relates to a seismic survey technique and can be used in seismic vibrator control devices. A known system for controlling a seismic vibrator, made in the form of a hermetic case with two movable arms, between which there is a hydraulic system G1. The disadvantages of the known system are the distortions of the control signal in the vibrator control path, as well as the low reliability and accuracy of the vibrator operation. A known system for controlling a seismic vibrator / containing a generator of a control signal, a computing unit, a digital recording device, an analog-to-digital one. a converter, a device, a precision generator, a precision generator, a drive motion controller, and an analog converter 2. In that system, when generating a signal recorded on the carrier (magnetic drum or disc) of the recorder, which represents a 5th recording device. the time scale of the control signal is violated, for example, by the fluctuations in the speed of movement of the recording carrier, which leads to distortions of the control signal in the control path of the vibrator. .. The purpose of the invention is to reduce the distortion of the control signal in the control paths of the vibrator. To achieve this goal, a derivative digital control device is inserted into the system, which is installed between the playback device and the digital-to-analog converter, and the control input of the digital control device is connected to a precision generator. The drawing shows a block diagram of a seismic vibrator control system. The control system contains a seismic vibrator 1, a seismic receiver 2, a cable 3, a seismic signal processing unit 4, a computational unit 5, a switch 6, a digital recording device 7, an IgG control generator 8, an analog-to-digital converter 9, a playback device 10, a controller 11 drive movements connected by a link of 12 s. a playback device, a precision oscillator 13, a digital control analogue 14 operating on a derivative digital-analog converter 15.

The seismic vibrator control system operates as follows.

The emitter 1 of the seismic vibrator is located on the earth's surface at some distance from the seismic receivers 2. The oscillating emitters are controlled by a signal arriving at the radiator through the input line 16. The excited seismic vibrations are directed into the earth's thickness, are reflected from the acoustic anomalies and returned to the earth's surface (arrow A shows the direction of propagation of seismic waves). Reflecting from the site 17, located deep in the earth’s thickness, the seismic waves are directed upwards and converted by the seismic receivers 2 into electrical signals. Electrically, the signals on cable 3 are fed to processing unit 4.

The vibrator control signal supplied to the input line 16 can be generated either by digital or analog means, with the digital form being the most up-to-date. One of the methods for generating a control signal by digital means is to create programs for a computing unit 5, the output of which is connected via a switch 6 to a digital recorder 7. A digital control signal can consist of a sequence of digital electric pulses, representing a predetermined form of control signal.

The control signal can be generated by the generator 8. This signal in the analog-to-digital converter .9 is converted into electrical iiM pulses, after which I control signal in digital form through switch 6 is fed to a digital recorder 7. Typically, for seismic exploration, the control signalSNSH has, range from 2 to 100 Hz.

The choice of the frequency range depends on the specific seismic and geological conditions. For computational unit 5, it is possible to create such a program / which provides the generation of a sequence of electrical pulses corresponding to the required control signal for given natural conditions.

The control signal obtained in the computing unit 5 can be reproduced in the playback device 10, and then used to excite the seismic radiator.

The playback of the playback device 10 is connected by a link 12 with a drive motion controller 11, to which the synchronization signal is applied.

from the precision oscillator 13. The latter also introduces a clock signal on the device 14 of the digital control with respect to the derivative, which serves to record changes in the time interval between the values of the digital word. The value of the digital word is sequentially input to a digital-to-analog converter 15, from which the desired analog control signal is taken.

Claims (1)

1. The patent of France 1397142, cl. G 01 C, published. 1965. 2, US Patent 3,293,317, Cl. 340-15.5, published. 1964. BUT / 7