| abstract |
A control system for an electro-hydraulically driven vibrator for the purpose of maintaining a constant phase relation between the output signal of the vibrator, passing into the earth, and a reference signal being used to drive the vibrator. The system operates on a digital basis and provides two digital sweep signal generators, each of which provides a train of time spaced voltage pulses of selected magnitude, in accordance with a corresponding train of timespaced time-words signals. One of these is a reference sweep signal generator and has a continuous application of time-words. The second is designed so that the sequence of time-words signals can be modified, that is, time-words are advanced or retarded, thereby effectively shifting the phase of the second, or driver signal generator, with respect to the first, or reference signal generator. The driver signal is used to control an electro-hydraulic vibrator. Feedback signals are provided from the output of the vibrator. These are compared with the reference signal and the result used to provide a feedback error signal, which controls the sequence of time-word signals which are sent to the driver generator. Thus, the two trains of output pulses, from the two generators, are relatively shifted in instantaneous phase, in accordance with the feedback error signal, by the shifting of the time-word sequence to the driver generator. |