Signal generation apparatus and method for seafloor electromagnetic exploration
First Claim
1. A cycloconverter for subsea electromagnetic exploration, comprising:
- a transformer having a primary side for receiving a high voltage low current signal of a first frequency and a secondary side for outputting a low voltage high current signal also of the first frequency;
a switching circuit connected to receive the low voltage high current signal from the secondary side of the transformer and to switch its polarity so as to generate an output signal having a significant component at a second frequency lower than the first frequency; and
a controller configured to control the switching circuit responsive to a measurement of the first frequency.
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Abstract
An apparatus for generating electronic signals for application in subsea electromagnetic exploration. A surface generated high-voltage low-current source signal stabilized at a first frequency is supplied to a deep-tow vehicle (18) via an umbilical cable (16). The high-voltage low-current source signal stabilized at a first frequency is supplied to a deep-tow vehicle (18) via an umbilical cable (16). The high-voltage low-current signal is transformed at the deep-tow vehicle to a high-current low-voltage a.c. signal by a transformer (52) within a cycloconverter (30). A semiconductor relay bridge (104) provides switchable rectification of the high-current low-voltage a.c. signal to provide a quasi-square wave at a second frequency, lower than the first frequency, for supply to a transmitting antenna (22) towed by the deep-tow vehicle. The times of the rectification switching are dependent on zero crossings of the high-current low-voltage a.c. signal. Allowable rectification switching times may be gated to occur only within pre-determined time windows to avoid noise-induced zero-crossing switching. The apparatus allows multiple transmission frequencies to be derived from a single stabilized source and improves spectral integrity by avoiding rectification switching at zero-crossings not occurring at the first frequency.
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Citations
5 Claims
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1. A cycloconverter for subsea electromagnetic exploration, comprising:
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a transformer having a primary side for receiving a high voltage low current signal of a first frequency and a secondary side for outputting a low voltage high current signal also of the first frequency;
a switching circuit connected to receive the low voltage high current signal from the secondary side of the transformer and to switch its polarity so as to generate an output signal having a significant component at a second frequency lower than the first frequency; and
a controller configured to control the switching circuit responsive to a measurement of the first frequency. - View Dependent Claims (2, 3)
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4. A method of controlling switching events in a cycloconverter during subsea electromagnetic exploration, comprising:
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providing a high voltage low current signal of a first frequency;
transforming the high voltage low current signal of a first frequency to a low voltage high current signal also of the first frequency;
measuring the first frequency; and
switching the polarity of the low voltage high current signal based on the measurement of the first frequency to generate an output signal having a significant component at a second frequency lower than the first frequency. - View Dependent Claims (5)
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Specification