Transmitting data at different frequencies in a logging while drilling tool

摘要

A LWD tool is disclosed comprising, a stator (150), a rotor (160) which rotates relative to the stator (150) thereby effecting a signal in the borehole fluid flowing therethrough, a brushless DC motor (100) coupled to the rotor (160) for driving the rotor, a position sensor (110) coupled to the motor (100) for sensing the rotational position of the motor, motor drive electronics (191) coupled to motor for driving the motor, and a microprocessor (91) coupled to the position sensor (110) and to the drive electronics for controlling the drive signals to the motor based on the actual and desired positions of the motor (100). By controlling the drive signal to the motor, the speed of the motor is controlled, thus effecting changes in frequency and/or phase of the signal in the borehole fluid or mud. With the ability to change the frequency and/or phase, different encoding techniques such as PSK-type and FSK-type can be used. Other preferred aspects of the invention include: choosing carrier frequency based on system noise; the use of magnetic positioner (130) and the coordination of the decelaration and acceleration of the modulator to correspond to desired magnetic positioner positions in effecting a phase shift; and jamming avoidance techniques utilizing the position sensor (110) and microprocessor (91).