Abstract: This invention concerns a synchronizing control for an electro-hydraulic seismic vibrator, which control utilizes a magnetic tape cassette reader that puts out a train of pulses of changing time spacing of a preselected pattern. This operates a counter which controls the address of a read-only memory which has a selected number of memory locations, each one holding a corresponding one of a sequence of digitized values forming a single cycle of a sine wave. By continuing to operate the counter, each of the values stored in the memory is sequentially placed in an output circuit to provide a digitized sinusoidal reference sweep signal. The cassette reader signal also drives a second counter through a frequency ratio control of the pulses provided by the cassette. By this means, the second counter can be varied to count at a different rate from the first counter.

Abstract: Apparatus for increasing the seismic data storage capacity of magnetic tape. A pair of storage registers store a sequential pair of digitized seismic data samples. A subtractor coupled to these two registers provides an output equal to the difference between the two stored samples. A decoder and a set of gates couples the difference word serially to a bit comparator starting with the most significant bit. The first logical "1" which is encountered and all the lower order bits of the same word are serially coupled to and written in a read/write memory. The decoder and gates cause a "0" to be written in a second read/write memory at the beginning of each data word, and "1's" to be written in addresses corresponding to the data written in the first read/write memory. The data in the read/write memories are addressed for reading by a read/address counter, which is incremented by an incremental shaft encoder on a drive motor of a tape recorder.

Abstract: A phase detector for detecting the phase difference between a pilot reference signal and a feedback signal generated by movement of a vibrator baseplate. The detector includes a phase shifter for providing a delayed reference signal phase-shifted from the pilot reference signal by 90.degree.. A pair of multiplier circuits generate the products of the pilot reference signal times the feedback signal and the delayed reference signal times the feedback signal. A pair of integrators integrate the multiplier outputs over one full cycle of pilot reference signal. A divider generates the quotient of the integrator outputs at the end of each integration cycle. This quotient is proportional to the tangent of the phase difference between the pilot reference signal and the fundamental frequency component of the feedback signal. An arctangent decoder circuit converts the divider output to the actual phase-angle difference.

Abstract: This is a seismic digital recording system for use where the seismic amplifiers are placed near the geophone locations and their outputs transmitted by common cable to the recording truck or recorded on magnetic tape at the geophone location. In such a digital recording system, it is impractical to use a high-speed, high gain-ranging amplifier of 15 or 16 bits range. In our design the gain-ranging amplifier is high-speed but employs fewer bits total range. The extra range is made up in a preamplifier which has a variable range of gain, which can be automatically set, but at slower speed. The invention involves a control system which is responsive to the output of an A/D converter which is connected to the output of the gain-ranging amplifier.