Variable inductor as downhole tuner
AssigneeSchlumberger Technology Corporation
InventorVincent Ernst
Life of this patent
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Abstract
A tunable LC circuit is used to trigger an electron discharge from an accelerator device, such as a Betatron. The circuit includes a coil as a first inductor having a first inductance electrically coupled in series with a capacitor. A second inductor having a variable inductance is electrically coupled, either in series or parallel, to the first inductor. The time to capacitor discharge is governed by: τLC=√{square root over ((L+LTUNE)C)}. Adjusting the inductance of the variable inductor (LTUNE) facilitates continuous adjustment of the discharge time. This is particularly useful when the LC values change in response to external stimuli, such as borehole temperature when a Betatron is used to log borehole features.
Claims18
A tunable LC circuit, comprising:
- a first inductor having a first inductance in series with a capacitor;
- and
- a second inductor having a second variable inductance coupled to the first inductor.
A modulator circuit for a Betatron having at least one magnetizing winding of first inductance, comprising:
- a low voltage D.C. power supply;
- a low voltage capacitor coupled across said power supply;
- a high voltage capacitor coupled across said power supply, the capacitance of said low voltage capacitor being much greater than the capacitance of said high voltage capacitor;
- the winding of said Betatron being coupled in inductive charging relation between said low voltage capacitor and said high voltage capacitor;
- a second inductor having a second variable inductance coupled to the first inductor;
- a current source operatively coupled between said Betatron winding and said high voltage capacitor for normally permitting current flow from said low voltage capacitor through said Betatron winding to said high voltage capacitor but preventing reverse current flow;
- and
- a switch effective to selectively reverse the direction of current flow between said low voltage capacitor and said high voltage capacitor to discharge the energy stored in said high voltage capacitor and said low voltage capacitor into said Betatron winding.
A method for tuning an LC circuit, comprising:
- coupling a first inductor with a capacitor;
- coupling a second inductor with said first inductor wherein said second inductor has a magnetically saturable core with an electrically conductive insulated signal winding about portions of the core to magnetically couple a signal current to the second inductor and a electrically conductive insulated bias winding wound around said core to magnetically couple a bias current to the second inductor and thereby vary the inductance of the second inductor to achieve a current pulse having a desired time from minimum to maximum.
A method to tune a Betatron having at least one magnetizing winding of first inductance in an LC timing circuit to accelerate electrons, comprising the steps of:
- coupling a capacitor in series with said at least one magnetizing winding;
- coupling a second inductor having a variable inductance to said at least one magnetizing winding;
- providing a source of A.C. current to said LC timing circuit;
- and
- adjusting the variable inductance to achieve a desired time to peak current.
Dependencies are inferred from the claim text.