| 摘要 |
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. The second counter also addresses the read-only memory, and the outputted digital signals are converted to an analog signal which is used as the drive sweep for the vibrator. The motion of the vibrator baseplate is detected by an accelerometer, the signal of which is doubly integrated and converted to digital form. One of two identical digital filters filters the reference sweep signal and the other the accelerometer signal. The filter outputs then go to a phase comparison network which controls the frequency ratio control of the second counter. When the reference sweep leads or lags the output signal from the accelerometer, the frequency ratio control advances the second counter at a higher or a lower rate, as necessary, to convert the second digital output of the memory to a correspondingly different phase, in order to correct the phase relation of the vibrator output and the reference sweep.
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